Selective electrochemical reduction of CO2 into energy-dense organic compounds is a promising strategy for using CO2 as a carbon source. However, efficient and selective earth abundant metal catalysts for the two reactions typically required for efficient overall CO2 electrolysis, namely the oxygen evolution reaction (OER) and CO2 reduction, are still scarce. We will present here an array of strategies inspired from biological systems to promote these reactions with high selectivity and efficiency. The importance of tackling these challenging reaction at multiple scale will be illustrated by a series of molecular and heterogeneous catalysts replicating enzymatic features, from their active sites including secondary features such as hydrophilic and hydrophobic domains to the overall shape of organs involved in gas trapping.[1-7]                                                                              

The direct CO₂ electrochemical reduction reaction (CO2RR) is a potential technology to convert waste CO₂ streams into valuable chemicals, using renewable electricity as a driving force. During this process a variety of carbon-based products such as CO, HCOOH and hydrocarbons can be formed. The selectivity of the CO2RR is determined by the nature of the catalyst interphase, which is dependent on the catalyst material, its morphology and the working electrolyte, among other factors. Therefore, it is necessary to get a holistic approach to fully understand the CO2RR and to get optimal catalytic results.

For this contribution we look at the influence of proton concentration on the selectivity of carbon based catalysts. Unlike hydrogen or methane generation, CO production has been shown to be independent of pH concentration on the NHE scale. Therefore, the proton concentration can be used to tune the CO/H₂ ratio. In aqueous electrolytes, for instance, the selectivity towards CO on Fe nitrogen-doped carbon is clearly enhanced at neutral pH whereas acidic conditions favored methane and hydrogen production. [1]

For this contribution we studied the CO2RR in aprotic media aiming to suppress the competing hydrogen evolution reaction (HER). We first studied a pure carbon electrode which in aqueous electrolyte selectively produced H₂, yet traces of CO were also obtained. By contrast, in an aprotic electrolyte (0.1M NBu4PF6 in acetonitrile) CO was obtained with a faradaic efficiency higher than 90%. Density functional theory (DFT) simulations confirmed this is attributed to the absence of protons, showing that certain carbon defects can reduce CO₂ into CO in both media. Nevertheless, carbon sites are predicted to be more active towards the HER and thus in aqueous media the formation of H₂ is the predominant process.

While it is remarkable that the pure carbon can selectively reduce CO₂, the process takes place at  high over potentials, this can be improved by intruding dopants. Metal nitrogen doped carbons, in particular, have been shown to be highly active towards the CO2RR in aqueous media. [2] Working in a non-protic electrolyte, resulted in suppression of both the HER and the CO2RR, as both reactions require protons. Nevertheless, the presence of small amounts of water resulted in a clear enhancement of the CO2RR while keeping a low HER activity. These results highlight the importance of proton concentration on determining the reaction selectivity. On one hand H^₊ concentration has to be limited to suppress the competing process of the HER. However, protons are also necessary to carry out the reduction of CO₂ into CO and methane. 

Energy-intensive thermochemical processes within chemical manufacturing are a major contributor to global CO₂ emissions. With the increasing push for sustainability, the scientific community is striving to develop renewable energy-powered electrochemical technologies in lieu of CO₂-emitting fossil-fuel-driven methods. However, to fully electrify chemical manufacturing, it is imperative to expand the scope of electrosynthetic technologies, particularly through the innovation of reactions involving nitrogen- and sulfur- based reactants as products from water/CO₂ electrolysis do not cover the full scope of industrial needs.

To this end, this talk focuses on my lab’s efforts in the co-electrolysis of CO₂ with additional small molecule reactants (NH₃, NO₃^-, SO₃^2-…) in generating products with C-N and C-S bonds like amides, urea, and sulfonates that are important as commodity and fine chemicals in the chemical industry.  In particular, I will discuss several new reaction pathways discovered towards several of the above-mentioned products and the application of operando techniques to understand the key C-N/C-S coupling steps in the reaction process.

Electrocatalytically driven CO₂ reduction reaction (CO₂RR) to produce alternative fuels and chemicals is a useful means to store renewable energy in the form of chemical bonds. in recent years there has been a significant increase in research efforts aiming to develop highly efficient CO₂RR electrocatalysts. Yet, despite having made significant progress in this field, there is still a need for developing new materials that could function as active and selective CO₂RR electrocatalysts.

In that respect, Metal–Organic Frameworks (MOFs), are an emerging class of hybrid materials with immense potential in electrochemical catalysis. Yet, to reach a further leap in our understanding of electrocatalytic MOF-based systems, one also needs to consider the well-defined structure and chemical modularity of MOFs as another important virtue for efficient electrocatalysis, as it can be used to fine-tune the immediate chemical environment of the active site, and thus affect its overall catalytic performance.

Our group utilizes Metal-Organic Frameworks (MOFs) based materials as a platform for imposing molecular approaches to control and manipulate heterogenous electrocatalytic systems. In this talk, I will present our recent study on electrocatalytic CO₂RR schemes involving MOFs, acting as: a) electroactive unit that incorporates molecular CO₂RRelectrocatalysts, or b) non-electroactive MOF-based membranes coated on solid CO₂RR catalysts (see illustrative TOC figure).

The electrochemical CO 2 reduction reaction (CO 2 RR) is an attractive method to produce renewable fuel
and chemical feedstock using clean energy sources. Although copper (Cu) is a well-known electrocatalyst
for the electroreduction of CO 2 to multiple hydrocarbons, it suffers from poor selectivity, efficiency, and
stability. In this work, a novel bimetallic Cu-Pd alloy anchored on two-dimensional Ti 3 C2 Tx -MXene
nanosheets was further converted to highly conductive three-dimensional Cu-Pd/MXene aerogel, which
acts as an excellent electrocatalyst to reduce CO 2 to formate with high selectivity of 93% and current
density of 150 mA/cm 2 . Compared with Cu-Pd aerogel, the newly designed Cu-Pd/MXene aerogel could
effectively decrease the overpotential and enhance selectivity and current density with great stability
during a long-term reaction. This simple strategy represents an important step toward experimental
demonstration of 3D-MXenes-based electrocatalysts for CO 2 RR application and opens a new platform for
the fabrication of macroscale aerogel MXene-based electrocatalysts that can be used for a range of
applications, including nanocomposites, electronic devices, and all-liquid microfluidic devices.

The electrochemical reduction of CO₂ (CO₂RR) with Cu-based catalysts has a rather poor selectivity towards C₂₊ molecules, such as ethylene and ethanol. Up to 16 different products can typically be formed during the process. [1] However, copper is the only known element with the ability to make C-C bonds and produce the desired C₂₊ products.[2] Therefore, it is key to gain a better understanding of the active sites of Cu-based electrocatalysts in order to improve the design and consequently the selectivity towards molecules such as ethylene and ethanol. This can be done, for example, by using well defined surfaces such as single crystals, providing insights into the reactivity of different exposed planes. It has beed shown that  ethylene is mainly produced on Cu (111) facets while a higher selectivity for methane was observed for Cu (100) facets. [3],[4]

In this study, cubic and octahedral Cu₂O nanocrystals predominantly exposing (100) and (111) facets were synthesized, respectively. Polyvinylpyrrolidone (PVP) was added during the synthesis as a capping agent to delicately control the ratio of (111) over (100) planes, yielding different shape Cu₂O nanostructures. [5] The presence of preferential cubic or octahedral shapes on the different synthesis was also confirmed by X-ray poweder diffraction (XRD), Moreover, the ratio of diffraction intensity for the (111) and (200) reflections showed an increase for the octahedral structure. Additionally, the synthesis procedure allowed the control of the size of the nanostructures between 400 and 800 nm as confirmed by SEM. Chronoamperometric measurements revealed that the cubic Cu₂O nanocrystals are more selective towards ethylene compared to the octahedral shaped particles. The cubic Cu₂O nanocrystals achieved a Faradaic efficiency for C₂₊ products of approximately 60% at a potential of -1.0 V vs. RHE. These results are in agreement with the observations on Cu single crystals, showing that the surface structure dependence for CO₂RR is maintained for Cu₂O catalysts.

Our sustainable future requires finding affordable and green routes to prepare nanostructured materials for more efficient energy conversion reactions. Compared to bulk materials, nanocatalysts show improved electrocatalytic activity due to their high electrochemically active surface area (ECSA) combined with reduced loadings of noble metals. Metal electrodeposition in deep eutectic solvents (DES) has emerged as a versatile, green and affordable alternative to prepare bimetallic nanostructures. DES are non-toxic solvents which show wide potential limits, enough conductivity, high solubility of the majority of the metals and do not require surfactant agents or additives for controlled growth of the nanostructures.^[1] In this work, we investigate the preparation of high surface area nanostructures of Cu-Au^[2] and Pd-Au^[3] with tunable structure and composition by electrodeposition in choline chlorine plus urea DES. We combine electrochemical methods with microscopy and spectroscopy techniques to characterize the electrodeposited nanostructured materials. We assess the increase of the electroactive surface area through the analysis of metal underpotential deposition (UPD) on the prepared films and, CO stripping on the Pd-Au bimetallic films, to investigate the effect of the Pd loading on the electrochemical response. Finally, Pd and Pd-Au nanostructures were tested for formic acid oxidation in comparison to extended polycrystalline surfaces. Overall, I show a simply and eco-friendly method to prepare mono and bimetallic nanostructures for different electrocatalytic reactions.

Global energy demand is increasing exponentially and the main source of energy is still based on fossil fuels, which are scarce and responsible for the majority of carbon dioxide (CO₂) emissions into the atmosphere. Green hydrogen has emerged as a promising energy vector to respond to this increasing energy demand and to decarbonize transportation, heating and fine chemicals sectors. On the other hand, electrochemical CO₂ conversion into energy-rich fuels and chemicals has gained significant interest as a potential strategy for simultaneously mitigating increasing global CO2 concentration.

Here we present a cost-effective copper-based electrocatalyst to evolve hydrogen with faradaic efficiencies close to 100%. Moreover, this electrocatalyst in presence of CO₂ is able to reduce it in formic acid with faradaic efficiencies close to 70%. Beyond the easy synthesis of this electrocatalyst and its high efficiencies for hydrogen evolution (HER) and CO₂ reduction reaction (CO₂RR), what really makes this material interesting is its behavior during the electrocatalysis. This copper-derived electrocatalyst enhance its currents as a function of time when evolves hydrogen increasing too the active surface area almost proportionally. While in its application for CO₂ reduction, its activity was studied when the electrode is reused several times, showing an increasing selectivity trend toward formic acid in each use.

Integrating the alkaline capture of CO₂ from the air with the electrochemical conversion of the obtained (bi)carbonate solution in one and the same system is among the most promising strategies in the field of Carbon Capture & Utilization (CCU) technologies. Thus far this approach has received little or no attention as a consequence of the challenging conversion of CO₂ from bicarbonate solutions as it mostly results in low Faradaic Efficiency (FE) and partial Current Density (CD) towards carbon products during the electrolysis and owing to the parasitic hydrogen evolution reaction (HER). Very recently, thanks to the advances in reactor design and in the understanding of the mechanism of bicarbonate electrolysis, promising results were obtained in terms of performance (i.e., >60% FE towards formate or CO at >50 mA cm^-2) [1] and as such provided us with the required knowhow to for the first time, construct and validate a proof-of-concept experimental setup where CO₂ is captured from the air with KOH, in the form of a 0.7 M (bi)carbonate solution, through Direct Air Capture and then converted to formate or CO in a zero-gap flow electrolyzer using a bipolar membrane in a Membrane-Electrode Assembly (MEA). The presented results provide a new opportunity towards upscaling the electrochemical conversion of CO₂, since integrating the capture and the conversion steps is a crucial step to enhance the economic feasibility of the CCU technology (energy-intensive CO₂ separation can be avoided) and thus increase its chances of industrial implementation.

The electrochemical reduction of carbon dioxide (CO₂) to hydrocarbons provides storage of renewable electricity into energy dense molecules while also neutralizing CO₂ emissions. Last decade has shown an unprecedented development towards its industrial application by reaching CO₂ reduction reaction efficiencies (>95 % for CO and 87 % for C₂H₄) thanks to the fine engineering of novel catalyst and membrane types. In chorus, the gas diffusion electrodes (GDE) and flow-type reactors have played a key role to overcome mass transfer limitation and steer the current densities up to industrially relevant values, e.g. ~1 A/cm².

Currently, most of the gas diffusion layers forming the backbone of the GDEs have been adopted from the proven processes such as fuel-cell and chlor-alkali systems. However they are not ideal for the large scale implementation and long term stability of CO₂ electrolysis due to the diverse nature of the reaction. In this work, we will show the main advantages and limitations of the three most common gas diffusion layers employed in the field of CO₂ electrolysis which are; nonwoven-, paper and cloth-GDEs with an identical catalyst layer obtained by sputtering of 150 nm thin copper film. By using an operando IR-thermography technique (filed patent), we mapped the temperature distribution profile of the GDEs until their failure by flooding. Thermal imaging results showed a smaller gradient and uniform temperature profile along the Cloth-GDL, which was attributed to the continuous fiber structure forming a straight electron path. On the other hand, the agglomerated PTFE flakes, large pockets and cracks of Paper-GDL were found as failure points to flooding by electrowetting and displayed a resistance to the electron path, evident from the higher potential and temperature value at elevated current densities. Conversely, very compact form of carbon nanoparticle and fiber structure of Nonwoven-GDL underwent premature flooding by the salt deposits and blocked CO2 diffusion to the catalyst layer. Coupled with an advanced ex-situ electron microscopy for post-mortem analysis , we have localized and matched the failure mechanisms of each GDE with a focus on the changes observed in the operando analysis during an hour long electrolysis at 250 mA/cm². Our results will provide the strategies for inspection and improvement for better performing GDEs which would be beneficial not only to CO₂ electrolysis but also to the upscaling of electrical energy conversion and storage devices.

The field of CO₂ electrolysis witnessed rapid development in recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. Iridium is almost exclusively used as the anode catalyst in polyelectrolyte membrane water electrolyzers. This practice quickly became a standard in CO₂ electrolysis due to its similarity to water electrolysis (oxygen evolution - OER is the anode process in both cases). An alkaline electrolyte solution is typically recirculated in the anode compartment to ensure a high reaction rate during CO₂ electrolysis. However, iridium is known to slowly but continuously dissolve in alkaline solutions. Additionally, while using iridium as the anode catalyst on a laboratory scale is acceptable, economic reasons urge the exploration of non-noble alternatives.

In my presentation, I am going to discuss alternative anode electrocatalysts that have been tried already in CO₂ electrolyzers. A closer look will be taken at Ni, which should be stable at least under the initial process conditions. We found that while Ni showed high activity (similar cell voltage to that with iridium) at the beginning of our experiments, it instantaneously started to decrease over time. If the anolyte is recirculated (typical scenario), the continuous carbonate transport through the anion exchange membrane decreases the bulk pH of the anolyte. In the case of the zero-gap electrolyzer cells employed in our study, the carbonate ion flux directly hits the anode catalyst layer, causing a high carbonate ion concentration in the close vicinity of the electrode. In parallel, H⁺ ions formed at the anode as the result of OER are not neutralized instantly (unlike in water electrolysis), which leads to an acidic surface pH. These two effects together alter the local chemical environment at the surface of the anode electrocatalyst leading to a gradual dissolution of Ni.[1] Based on our measurements, a set of criteria will be described that have to be fulfilled by an anode catalyst to achieve high performance.

In the second part of my talk, I am going to provide an outlook on replacing OER at the anode with various alternative anode reactions (such as electrocatalytic alcohol oxidation) to deliver high-value products in parallel with increasing the energy efficiency for the whole process.[2] A closer look will be taken at issues regarding the selectivity and stability of these systems along with discussing possible mitigation strategies and future research directions.

Cu is the only monometallic catalyst that can reduce CO producing a large variety of valuable compounds. However, the efficiency and selectivity towards specific products is highly affected by the structure properties of the catalyst and the composition of the electrolyte.[1]

Herein we have investigated the effect of the pH and the anion specifically adsorbed on the surface, on the structure and properties of the Cu(111) and Cu(100)-aqueous electrolyte interface.[2–4] Experiments under potential control were conducted on well-defined Cu single crystalline electrodes, and in presence of CO, to assess the electrolyte and surface orientation effect on the onset potential for the CO reduction.[3] We specifically used cyclic voltammetry in combination with other electrochemical approaches such as the CO displacement technique and laser induced temperature technique, in order to shed lights into the distribution of the surface charge and adsorbed electrolyte species across the whole potential window.[2–4] We experimentally showed that the structure of the Cu-electrolyte interface, at different pH and in presence of different anions, controls the onset potentials of the CO reduction. Lastly, we have investigated lead underpotential deposition to assess the different facets and domains in nanostructured copper, which is relevant to design more efficient electrocatalysts for the CO reduction. [5]

Figure 1 shows the cyclic voltammogram (CV) of Cu(111) in contact with 0.1 M phosphate buffer solution at pH 5 and in presence of CO, recorded at a short potential window (blue line) and long potential window (red line), 50mV/s.

Efficient conversion of solar energy into molecules for energy storage and other purposes is one of the most important challenges for sustainable energy systems of the future. Particularly directly coupled photovoltaic (PV) assisted electrochemical (EC) processes, like e.g., PV-assisted water splitting, are of interest. In most practical cases, PV and EC devices are developed separately and then merged at a later stage to verify their performance as a PV-EC system. Enormous efforts of many groups in catalyst development produce increasing number of new catalysts every year. In turn photovoltaic community continues optimization of variety of PV technologies. In this situation, it would be useful to be able evaluate potential of one or other catalyst pair in combination with different PV technologies without building and optimizing an experimental device. To address this issue, we have recently developed a simple method to assess limit of solar-to-hydrogen efficiency (STH) of a specific electrolyzer based on the “reverse analysis” of its polarization curve [1]. We show that despite the complexity of the parameter space, there is a surprisingly simple way to estimate the limit of efficiency in any PV-assisted electrolyzer system.

The maximum STH for a specific electrolyzer is achieved when the current-voltage (IV) characteristics of the PV device crosses polarization curve of the EC device at maximum power point (MPP). Conversely, each point on the EC polarization curve can be considered the MPP of a PV device optimally coupled to the EC device. Therefore, at each point on the polarization curve, the minimum PV efficiency and maximum EC efficiency can be calculated for a specific irradiance. The product of both efficiencies generates the STH limit that can be attained at that specific point on the polarization curve. The result of the transformation is the dependence of the STH limit on the PV efficiency at the assumed irradiance level and optionally ratio of the active areas of PV and EC devices. This "reverse analysis," carried out with elementary math, does not involve any modeling or analysis of PV IV characteristics and provides a quick simple way to quantify the potential of any electrolyzer.

In our paper we present the principle of the reverse analysis using an example NiMo/NiFeO_X catalyst pair. Next, we show how using this analysis losses in an experimental PV-EC combination can be identified and quantified. We present extended set of results of reverse analysis applied to a variety of PV-EC combinations described in the literature. Finally, we discuss how this analysis can be applied to different electrochemical devices coupled to PV like e.g., PV-assisted CO₂ reduction.

TOC Figure. Principle of the reverse analysis: (a) at each point on the polarization curve, minimum PV efficiency and maximum EC efficiency are calculated; (b) the product of both efficiencies generates the STH limit at the specific point; (c) the result of the transformation presented as STH limit vs. PV efficiency.

Energy surplus, if not utilized, are dumped as waste energy in the form of heat, not to mention adding carbon footprint to our daily operations. Yet, developing countries struggle to meet their demand and distribution schedule of energy leading to rotational brownouts. Research on energy generation, storage, and release has been continuously rolling. Hydrogen, generated from water splitting, is postulated as one of the most promising alternatives to fossil fuels. In this context, direct hydrogen generation by electrolysis and fixation to graphene oxide (GO) in an aqueous suspension could overcome storage and distribution problems of gaseous hydrogen. Herein, approaches of hydrogenating graphene oxide were studied primarily by time-resolved Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR).

GO films, utilized as electrode for hydrogen evolution reaction with dynamic modulation of the potential difference, favoured 160% increase of C-H bond formation. Epoxide ring opening leading to hydroxyl groups suggests that these groups play a key role in hydrogenation. FTIR revealed characteristic -CH₂ and -CH₃ vibrations. This shows that hydrogenation is significantly also occurring in defective sites and edges of the graphene basal plane, rather than H-C(sp³). Partial reversibility was observed by in-situ Raman when applying a cyclic voltammetry caused by a reversible reaction present in the 0.34 to -1 V_RHE range.

Photocatalytic hydrogenation was also explored. Metal organic frameworks (MOF) of graphene oxide, Ni²⁺, Cu²⁺ were found to acquire -CH₂ and -CH₃ moieties upon irradiation by a 75 W xenon lamp with TiO₂ photocatalyst. The dispersing media and hole scavengers (water, methanol, and sulphite) were also found to affect the fixation of hydrogen in the (MOF). This method has demonstrated successful evolution of H-C(sp³) in the GO MOF whereas graphene-like structure (loss of oxygen functional groups) is produced when GO was subjected to the same irradiation technique.

One of the major limitations of renewables is their intermittent character which  depends on  climate conditions. The problem is a complete disconnection between energy production and demand. Consequently, the storage of energy surpluses from renewables becomes a necessity. To tackle this problem, in this work we propose an efficient way of energy storage based on using green hydrogen as an energy vector. The aim is to develop efficient systems for hydrogen storage in the form of chemical bonds based on Liquid Organic Hydrogen Carriers (LOHCs) [1].

From a chemical view, the key point of efficient LOHCs lies in the design of suitable catalysts and processes for the conversion and reconversion of hydrogen into chemical bonds. In this work, we describe our preliminary results in the field [2][3] and the last results in electrocatalytic dehydrogenation of amines and the catalytic hydrogenation of nitriles as efficient systems for hydrogen  storage in the form LOHCs.

The production of green hydrogen for water electrolysis is very promising for the development of a zero-carbon-emission energy structure. However, proton exchange membrane (PEM) electrolyzers, which operate in acidic media, are limited by the slow kinetics of the oxygen evolution reaction (OER) at the anode. Additionally, the anode requires high amounts of scarce precious metals like Ir as catalysts¹. An inherent need for developing preparation methods to decrease mass loadings and enhance activity and stability has therefore arisen. We introduce a feasible and easy way to prepare IrO_x catalysts by galvanic displacement of electrodeposited Co and Ni on polycrystalline Au surfaces. We performed the electrodeposition of Co and Ni on gold beads in a deep eutectic solvent (DES) – a non-toxic solvent with a broad potential window and high solubility of many metals². We fabricated Ir nanoparticles by employing galvanic displacement of Co and Ni in aqueous solutions of IrCl_4, and then electrochemically oxidized the metallic Ir. Our preparation of IrO_x catalysts replaces complicated plating methods by the galvanic displacement technique and replaces the use of surfactant agents during electrodeposition by a green DES electrolyte. We evaluated the activity and stability of the IrO_x catalysts with state-of-the-art Ir-based catalysts. The IrO_x-Ni displayed enhanced activity and stability in relation to the IrO_x-Co in line with previous reports³.

The requirement of the scarce element iridium for PEM electrolyzer anodes is a potential bottleneck in the transition to a fossil-free society. Replacing iridium is difficult due to the harsh conditions at the PEM anode of high potential and low pH. Only a handful of elements are stable as a solid phase in the region of their Pourbaix diagram corresponding to these conditions, most of which are either not conductive and/or not active for water oxidation. Ruthenium, though less stable and almost as rare as iridium, is an interesting candidate because its oxides (RuOx) have higher activity for water oxidation than those of iridium (IrOx). This talk will describe trends in the activity and stability of ruthenium dioxide at low overpotential. We use in-situ detection of O2 to distinguish water oxidation from charging currents [1] and isotope-labeling to probe the mechanistic coupling of water oxidation and catalyst degradation [2]. Ruthenium and iridium are also interesting in that both form rutile oxides, like most of the other elements that are stable (but inactive) under PEM anode conditions. Insights from IrO2 and RuO2 can therefore be transferred to novel solid-solution rutile oxides of the form AxB1-xO2. This talk will also provide a perspective on this approach to noble-metal-free PEM anode electrocatalysts.

Producing electrodes that comprise highly active but low-cost catalysts for water splitting reactions is still a great challenge for developing new technologies for green energy. In the last few years, transition metal chalcogenides such as NiSe and CoSe were studied as electrochemical catalysts, displaying good electrocatalytic activity. Combining Ni and Co to form ternary compounds allows tuning the active sites for the reaction. In addition, NiSe and CoSe are photothermal materials, where irradiating with light leads to a substantial increase in their temperature.[1] Combining these two functionalities, these materials can be bifunctional, such that their heating contributes to the apparent catalytic reaction rate.

Ternary (Ni_xCo_y)Se nanoparticles were synthesized via a solvothermal method. The resulting nanoparticles were 15-30 nm in size, with a hexagonal crystallographic structure. The ternary nanoparticles demonstrated enhanced electro-catalytic activity towards the hydrogen evolution reaction in acidic conditions. (Ni_0.25Co_0.75)Se exhibited a significantly improved HER performance relative to the binary compounds with an overpotential of 190 mV at 10 mA cm^-2 and a Tafel slope of 53 mV dec^-1. As for the photothermal performance, (Ni_0.9Co_0.1)Se proved to be the most efficient photothermal material in the set. Future work will focus on utilizing them for photo-thermal assisted electrochemistry and evaluating the added value of such setups.

Nitrogen fixation has shaped our society over the past two centuries, providing ammonia derived fertilizers through the Haber-Bosch process to now feed more than half the world population. However, its production is responsible for >1% of our greenhouse gases emissions.[1] It is therefore essential to find alternative synthesis methods sourced by renewable energies.

The electrochemical Li-mediated nitrogen reduction to ammonia (NRR) provides a more sustainable alternative to this challenging reaction.[2,3] This system, operating in a non-aqueous electrolyte analogous to the ones used in Li-ion batteries, provides tangible selectivity towards NH3.[3–5] Just like in Li-ion batteries, a passivating Solid-Electrolyte Interphase (SEI), made of electrolyte degradation products, forms at the cathode of the NRR system. This SEI likely plays a role in controlled proton activity at the electrode surface, limited hydrogen evolution and thus the observed selectivity.[6–8] Consequently, characterisation of this interface (and of the whole system) is vital.

The work presented here expresses guidance for reliable and in-depth electrochemical characterisation of the NRR system and its SEI, all through the lens of a new non-aqueous electrochemical cell design. Drawing further inspiration from batteries, considerations on the cell’s three-electrode geometry,[9–11] construction of a true reference electrode[10,12–14] (as opposed to quasi-reference electrodes in current setups in the field),[3,5,15] and cathode/anode processes separation will be under investigation. As a result, we propose and demonstrate an ideal setup for potential-controlled NRR electrochemistry, capable of measuring accurately the different electrochemical processes occurring over the course of this elusive reaction. Improvements in the accuracy, consistency and reproducibility of the electrochemical measurements resulting from this cell design will be illustrated through the study of a variety of electrolyte architectures.

Amines are compounds very sensitive to oxidation, and a wide array of products may be generated depending on the oxidant.¹ A particularly challenging oxidation is the conversion of a primary amine to a nitrile. In this work, the electrochemistry of primary amines to nitriles is explored using porous Ti/Ni alloys electrodes. These electrodes were recently developed in our group and proved very active in the water splitting oxidation achieving very low overpotentials.² Here, the electrodes have been used for the oxidation of amines to nitriles. A selection of primary amines have been evaluated to understand formation of secondary reactions that reduced their yield. For example, attachment of the amines to the electrodes and degradation in the reaction media has been reported frequently.³ Several conditions were screened to reduce these secondary reactions such as the use of solvents and their mixtures or modification of pH.  Under optimized conditions quantitative conversions and high yields are obtained in the electrochemical reaction of primary amines to nitriles.⁴

Upgrading processes are required to improve the quality of raw bio-oil and thereby increase their viability of bio-based fuel usage. Electrochemical upgrading of bio-oil can be an appealing alternative to current upgrading technologies, as they operate at moderate reaction conditions and can employ the expected surplus in electricity due to increasing capacities of renewable energy installations. One way to lower the acid content in bio-oil and thereby improving the quality of the bio-oil is by Kolbe electrolysis. In Kolbe electrolysis, acids are converted to (non)-Kolbe products and carbon dioxide. The reaction conditions strongly influence the product distribution. The influence of electrolyte pH is studied in literature, however its effect on the product outcome is not yet fully resolved. Contradictory observations and conclusions with respect to performance stability have been reported. Therefore, this work investigates the influence of electrolyte pH on the reaction-time and pH dependent product selectivity during Kolbe electrolysis of acetic acid on platinum.
In this study Kolbe electrolysis of acetic acid on a platinum anode in aqueous electrolytes is addressed with a particular focus on electrolyte composition. We will first disclose that a pH similar to, or larger than the pKa of acetic acid is required to favor formation and homocoupling of methyl radicals towards the Kolbe product ethane. However, extended duration of electrolysis of acetate at basic pH results in loss of Faradaic efficiency to the Kolbe product (ethane), compensated by the formation of the Hofer-Moest product (methanol). We postulate that the observed change in selectivity is caused by the dissolution of CO₂, resulting in enlarged concentration of (bi)carbonate near the electrode electrolyte interface. During the presentation we present our current understanding of the electrode-electrolyte interface and we will provide evidence that the spatial spacing between two methyl radicals is increased which lowers the dimerization rate. Finally, we will discuss the implications of our observations for practical applications, like bio-oil upgrading.

Nowadays, the search and development of economic and environmentally friendly synthetic procedures, alternative to traditional ones energetically fed by fossil fuels, is essential to avoid not only climate change, but also the inexorable depletion of such energy resource. Within this context, electrocatalysis has emerged as a suitable synthetic methodology that avoids the use of harsh reaction conditions and fossil fuels. Besides, in electrochemical approaches, the application of an electric potential difference allows performing chemical reactions that in normal atmospheric conditions would not take place. 

The main chemical procedures studied in electrochemistry are water splitting and CO₂ reduction. In both cases, the oxygen evolution reaction (OER) takes place at the anode, providing the electrons and protons needed in the cathode for the generation of H₂ in water splitting or the conversion of CO₂ into valuable species, such as CH₄ or CH₃OH. The OER produces O₂ that despite being a very important compound, its price in the market is very low, which limits the economic viability of the process and ultimately reduces the interest in this technology.[1] Furthermore, this reaction exhibits large overpotentials when using catalysts based on earth abundant materials, limiting energy conversion efficiency.[2] For these two reasons, there is a growing interest to find alternative reactions to OER at the anode that, by one side, reduce the overpotentials needed and by the other, produce compounds with higher added-value and interest for the chemical industry.[1,3] In this framework biomass valorization, has emerged as an attractive substitute to the oxidation of H₂O.[4] Herein we present our studies in the electrochemical oxidation of 5-hydroxymethylfurfural, a species derived from biomass, as an alternative reaction to OER that allows obtaining 2,5-furandicarboxylic acid (FDCA), a useful building block in the pharmaceutical and polymer industry.[5,6]

‘Water-in-salt’ type of electrolytes are highly explored in the recent past for  its applications in aqueous batteries. Such electrolytes decreases the hydrogen evolution reaction (HER) by extending the water stability window which can be useful for other electrochemical reactions like CO₂ reduction reaction or N₂ reduction reaction (NRR) as HER is the main competitor reaction, where such processes are highly important in chemical industry. For example, development of methods for economically feasible greener ammonia (NH₃) production is gaining tremendous scientific attention due to its importance in fertilizer industry and it is envisaged as a safer liquid hydrogen carrier for futuristic energy resources. In this aspect, electrochemical reduction reaction of nitrogen to ammonia in aqueous electrolyte is a promising way. In our research, an aqueous electrolysis based NH₃ production in ambient conditions is discovered, which yields high faradaic efficiency (~12%) NH₃ via NRR at lower over potentials (~ -0.6V vs. RHE or -1.1V vs. Ag/AgCl) on polycrystalline copper (Cu) bypassing HER.¹ Li⁺ based aqueous electrolyte is used in varying Li⁺ concentration as electrolyte, where the role of Li⁺ in tuning the heterogeneous reaction is established by theory and experiments.^2-4 It is observed that the HER activities of metals such as Pt, Ir, and Pd are suppressed by increasing Li⁺ concentration whereas that of Au, Fe, and Ni augmented with increasing Li⁺ concentration. Here the tunability in the metal-hydrogen (M-H) bonding energy with Li⁺ is experimentally and theoretically established, and the studies show that tunability in the HER properties of both noble and non-noble metals can be achieved irrespective of the pH (0 and 13) and counter ions (TFSI^-, Cl^-, ClO₄^-, NO₃^-and OH^-) by tuning the M-H bond energy using Li⁺.

Transition metal phosphides (TMP) are a promising materials family that has been studied extensively. Still, synthesizing complex and ternary phosphides in a reproducible manner is a challenge, due to the various available oxidation states and crystallographic phases. The various reactivities of the precursors and phase segregation often produce structure of diverse morphologies and compositions. For elucidating the intrinsic properties of these structures as catalysts, such synthetic control is crucial. Here, I will describe a few methods to produce complex ternary structures and their electro-catalytic activity towards hydrogen evolution (HER), oxygen evolution (OER) and alcohol oxidation.

Specifically, I will present a comparative study that illustrates the catalytic activity of three Ni-P phases towards hydrogen production through electrochemical water reduction as well as hydrogen retrieval by hydrolysis of hydrogen storage materials (ammonia-borane and NaBH₄). I will show that Ni₁₂P₅ was recognized as a suitable platform for the electrochemical production of γ-NiOOH—a particularly active phase—because of its matching crystallographic structure. An additional incorporation of tungsten by doping produces surface roughness, increases the electrochemical surface area (ESCA), and reduces the energy barrier for electron-coupled water dissociation (the Volmer step for the formation of H_ads). We explored the three different phases of nickel phosphide also for the electro-oxidation of methanol, ethanol, isopropanol, ethylene glycol, and glycerol. Ni₁₂P₅ exhibits excellent activity (210 mA cm^-2 at 1.72 V vs RHE), durability, and mass activity (~4.2 A mg^-‍1), outperforming the state-of-the-art catalysts. The high selectivity of the reaction and the large suppression of further oxidation to CO₂ are a marker of a preferred bidentate adsorption configuration that conveys a specific O–H activation reaction path. The catalysts show excellent activity towards alcohol oxidation and durability, likely thanks to the mild conditions required for the process, which allow the formation of a regenerating thin active layer of oxidized nickel.

Current ammonia production via the Haber Bosch process requires high pressures, high temperatures and consumes >1% of our current fossil fuel production. To the contrary, nitrogenase in nature catalyses N₂ reduction at room temperature and atmospheric pressures.  The translation of the activity and selectivity of nitrogenase to a solid inorganic surface would enable the efficient on-site on demand synthesis of ammonia, powered by renewable electricity.

Amongst solid electrodes, thus far, only lithium based electrodes in organic electrolytes can catalyse N₂ reduction to NH₃.[1,2] Significant improvements are required to bring the lithium mediated system to an industrial reality; nonetheless, the field is progressing quickly, as we documented in a recent commentary.[3] Nonetheless, we lack comprehensive insight into the factors controlling the reaction.

In this talk, I will discuss why the lithium mediated system is unique amongst solid electrodes in its ability to reduce N₂ to NH₃. Our data using a combination electrochemical experiments, operando and ex-situ characterisation, and density functional theory calculations.[4] I will draw from concepts from enzymes, homogeneous catalysis and battery science. On this basis, I will discuss the most promising avenues towards more efficient N₂ reduction.

Electro-organic synthesis has attracted many attentions in the last years due to the possibility of using renewable feedstocks like CO₂, CO and N-based compounds to generate valuable products. Among many possible reactions, C-C and C-N bond forming reactions represent an important synthetic class because C2+ products and amine derivatives, respectively, play crucial roles in various applications in synthetic chemistry.

CO₂ emitted in the atmosphere has been used as a feedstock for the synthesis of chemicals and fuels, although C2+ products are more attractive because of they have wider applicability and higher energy density [1], while NH₃ derivatives are used to generate amines and amino acids [2] .

Here we studied both C-C and C-N coupling reactions using reductive electrochemical transformations.

The synthesis of C2+ products from the electrochemical reduction of CO₂ was investigated on Cu-oxide derived nanoparticles. Our results showed the reaction is dependent on the electrode surface structure and proton concentration. Using online GC, ethylene and propanol were detected as products on Cu cubic nanoparticles, whereas on Cu polycrystalline, such C2+ products were not detected.

In order to enhance the spectrum of products, CO₂ has been also considered in the coupling reaction with other organic molecules, i.e. aldehydes, to make carboxylic acids via electrocarboxylation. Our initial results showed CO₂ reacts with butanal via C-C coupling to yield the corresponding carboxylic acid, in absence of CO₂, the electrochemical reduction of butanal leads only to dimers.

We have also investigated the electro-reductive amination of benzyl alcohols to benzylamines in aqueous solvent. Using TEMPO-immobilised graphite electrode, benzyl alcohol was selectively oxidized to benzaldehyde (Figure 1), while in the cathode, t-butylamine was converted into imine, which acts as the main intermediate to the C-N bond formation. Using the electrochemical conditions displayed in scheme 1, MS and NMR data analyses showed faraday efficiency (FE) of 12% towards benzylamine.Despite the low FE, this work opens an opportunity to the synthesis of important fine chemical by using simple renewable feedstocks.

References:

[1] da Silva, A. H. M.; Raaijman, S. J.; Santana, C. S.; Assaf, J. M.; Gomes, J. F.; Koper, M. T. M. Electrocatalytic CO2 Reduction to C2+ Products on Cu and CuxZny Electrodes: Effects of Chemical Composition and Surface Morphology. Journal of Electroanalytical Chemistry 2021, 880, 114750.

[2] Jeong Eun Kim, Seungwoo Choi, Mani Balamurugan, Jun Ho Jang, Ki Tae Nam. Electrochemical C–N Bond Formation for Sustainable Amine Synthesis. Trends in Chemistry, November 2020, 2, 11.

Nitrate (NO2-) is the world’s most widespread surface and ground water contaminant that causes adverse effects on human health such as methemoglobinemia (“blue baby syndrome”) and cancer. Most abiotic nitrate removal strategies center on the use of ion exchange resins. Ion exchange resins are effective, yet are not sustainable the process generates a large amount of waste. Biological approaches are inapplicable for removal of high nitrate ions and large scale applications as well as possibility of bacterial contamination in the drinking water.  Electrocatalytic NO3- remediation; however, is one emerging approach for nitrate removal which does not produce waste as NO3- is converted directly to inert dinitrogen (N2) gas. The main challenge with electrocatalytic NO3- reduction is the low NO3- conversion yield, poor N2 selectivity, and lack of understanding regarding catalyst stability. The production of equally harmful contaminant intermediate species such as nitrite (NO2-) and ammonium (NH4+), has also limited the applicability of electrochemical routes for nitrate remediation. Electrocatalytic NO3- valorization is another emerging approach for nitrate removal. Here, NO3- is converted directly to ammonium (NH4+). The main challenge with valorization of NO3- is the low activity and selectivity of the NO3- to NH4+ and the structure sensitivity studies are insufficient. Here, we will describe an investigation on the electrocatalytic properties of palladium (Pd) and copper (Cu) which contains structured surfaces and coatings. The primary aim is to identify which facets and surfaces are highly active and selective for nitrate and nitrite reduction. Engineering the structure of Pd and Cu that enhances the NO3- removal efficiency and enables to steer the selectivity toward N2 and NH4+. To achieve the real-life applications, we also verify the long-term operations for the developed electrocatalysts.Nitrate (NO2-) is the world’s most widespread surface and ground water contaminant that causes adverse effects on human health such as methemoglobinemia (“blue baby syndrome”) and cancer. Most abiotic nitrate removal strategies center on the use of ion exchange resins. Ion exchange resins are effective, yet are not sustainable the process generates a large amount of waste. Biological approaches are inapplicable for removal of high nitrate ions and large scale applications as well as possibility of bacterial contamination in the drinking water.  Electrocatalytic NO3- remediation; however, is one emerging approach for nitrate removal which does not produce waste as NO3- is converted directly to inert dinitrogen (N2) gas. The main challenge with electrocatalytic NO3- reduction is the low NO3- conversion yield, poor N2 selectivity, and lack of understanding regarding catalyst stability. The production of equally harmful contaminant intermediate species such as nitrite (NO2-) and ammonium (NH4+), has also limited the applicability of electrochemical routes for nitrate remediation. Electrocatalytic NO3- valorization is another emerging approach for nitrate removal. Here, NO3- is converted directly to ammonium (NH4+). The main challenge with valorization of NO3- is the low activity and selectivity of the NO3- to NH4+ and the structure sensitivity studies are insufficient. Here, we will describe an investigation on the electrocatalytic properties of palladium (Pd) and copper (Cu) which contains structured surfaces and coatings. The primary aim is to identify which facets and surfaces are highly active and selective for nitrate and nitrite reduction. Engineering the structure of Pd and Cu that enhances the NO3- removal efficiency and enables to steer the selectivity toward N2 and NH4+. To achieve the real-life applications, we also verify the long-term operations for the developed electrocatalysts.

Electrochemistry plays a focal role in the development of better and more efficient catalytic processes for the use of electricity to form or break chemical bonds.

This discipline is closely associated with the development of new renewable energy solutions, such as energy storage (electrolysers, ammonia and other renewable fuels) and chemical production (from CO or biomass). In particular, electrocatalysis has allowed in recent years to achieve significant development on material development and reaction optimization for processes aiming at the synthesis of chemicals and renewable fuels. With this symposium, we want to highlight the scientific excellence in this field.

This discipline is closely associated with the development of new renewable energy solutions, such as energy storage (electrolysers, ammonia and other renewable fuels) and chemical production (from CO or biomass). In particular, electrocatalysis has allowed in recent years to achieve significant development on material development and reaction optimization for processes aiming at the synthesis of chemicals and renewable fuels. With this symposium, we want to highlight the scientific excellence in this field.

Materials and electrochemistry of N-containing compounds
Materials and electrochemistry of carbon dioxide reduction
Electrocatalytic synthesis of high-value compounds: new routes and materials
Electrochemistry for the valorization of biomass

Density functional theory (DFT) calculations at level of the generalized gradient approximation (GGA) are often used in computational electrocatalysis models [1]. This is because DFT-GGA functionals provide fair descriptions of metals at reasonable computational expenses. In this talk, I will first show that the common practice of using DFT-GGA functionals usually entails large numerical errors for the description of molecules, particularly those with multiple bonds, and how to mitigate them by means of a simple and intuitive semiempirical method [2, 3].

Furthermore, I will show that molecular errors have an impact on calculated equilibrium potentials and free-energy diagrams of electrocatalytic reactions, as observed for CO₂ reduction to CO, O₂ reduction to H₂O and H₂O₂, O₂ evolution, and reactions within the nitrogen cycle [2, 4-6]. Finally, I will show that molecular errors appreciably modify Sabatier-type activity plots [6], such that different guidelines for catalyst design are obtained depending on whether or not molecular errors are corrected. The main conclusion is that it is generally advisable to use gas-phase corrections in screening routines for electrocatalytic materials.

To further expand fuel cell technology, a full understanding of the processes taking place at the surface of the electrodes is needed. After decades of investigation, platinum (Pt) is still the single metal with the highest electrocatalytic activity for the reactions taking place within a fuel cell. It has been shown that its catalytic properties can be further exploited by tuning the surface structure and composition. Therefore, preparing and understanding bimetallic surfaces is of paramount importance if one is to improve fuel cell performance [1].

Bi-metallic catalysts with well-defined surface structure can be prepared by depositing adatoms on Pt single crystal electrodes  [2], through the formation of surface alloys by co-deposition and gently annealing [3], or, as in this study, by preparing bulk alloy single crystal surfaces [4]. Here, the preparation of Pt–Pd bulk alloy single crystal electrodes following a modification of the Clavilier bead method has been revised. The surface composition and structure of the electrodes have been analyzed by X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED), respectively, pointing out that the surfaces prepared by this methodology are well-defined and give rise to surface compositions close to the nominal ones. Subsequent correlation between surface structure and composition and the voltammetric response has been assessed by performing cyclic voltammetry in different supporting electrolytes, displaying a characteristic and reproducible response for each surface.

Reportedly, very few studies have been accomplished for fuel cell reactions on well-defined bulk Pt-Pd alloys. Here, we will also show the electrocatalytic behavior of a collection of Pt-Pd single crystal surfaces for certain reactions of interest, such as formic acid oxidation and oxygen reduction reaction. Therefore, this contribution is a step forward towards the understanding of the combined role of surface structure and composition of Pt-Pd bulk single crystal electrodes in their catalytic behavior.

Electrochemical reduction of NO_x, CO₂, N₂ and combinations hold the promise to be a cornerstone for sustainable production of fuels and chemicals. Importantly, all reactions share a direct competition with hydrogen, and furthermore, several products are formed from each reactant of these reactants.

For electrochemical CO₂, a complex reaction, it has been shown to give multiple different products depending on the metal catalyst [1]. The unique copper catalyst, as the only metal catalyst has the ability to bind *CO without the coadsorption of *H, which results in a high-value multiple-carbon product distribution [2].

For electrochemical NO_x, also multiple products are formed; N₂O, N₂ and NH₃[3]. Uniquely again the copper catalyst stands out with the ability to bind *NO without the coadsorption of *H, which enables copper to produce ammonia [4].

For electrochemical N₂ reduction to ammonia (NH₃) the interest at ambient conditions is burgeoning [5-6]. Most interesting for the direct electrochemical N₂ reduction in aqueous there is not a “copper” catalyst [7], and instead, the reaction is limited to the non-aqueous lithium-mediated system.

In this talk I will give a unified approach to these reduction reactions versus hydrogen:

►  Show an original and simplistic view of reduction reactions versus hydrogen by investigating the *NO, *CO and *N₂ binding energies versus the *H binding energies. This gives direct insight into the product formation for NO_x and CO₂ reduction, and the challenge of the direct N₂ reduction reaction.

►  Show how one can use these molecular binding energies versus hydrogen in combination to form products beyond the typical reduction reaction products, which reduction reactions are possible based on this framework and how to challenge it [8].

Electrochemical reduction of CO₂ to fuels has attracted a great deal of attention in recent years as a potential solution to close the carbon cycle [1]. In search for novel catalyst materials, we present in this study density functional theory-based screening of heteroatom-doped transition metal nitrides [2]. We first examine zinc blend and rock salt polymorphs of transition metal nitrides and then consider doping the surface with 25% B, P, Sb, Bi, and C heteroatoms [3]. We fully assess the stability and activity of the examined catalysts. The catalytic activity is measured by the calculated limiting potential, and the stability is assessed against hydroxyl (*OH) poisoning as well as dissolution under CO reduction relevant potentials. Of the screened nitrides, many are predicted to be active for the CO reduction reaction but only a few are stable under electrochemical conditions. In particular, on nearly all of the metal nitrides with a desired catalytic activity for CO reduction, either the competing hydrogen evolution reaction prevails over CO reduction or *OH poisoning occurs at CO reduction onset potentials. We identify five promising candidates including P-doped NbN, C-doped VN, P-doped VN, TiN, and Sb-doped TiN. Ultimately, this study emphasizes the relevance of stability under electrochemical conditions and the importance of taking into account the competition between the CO reduction, hydrogen evolution, and *OH reduction reactions under electrochemical conditions.

The insertion of heteroatoms with different electronegativity into a carbon network can greatly tune its electronic, optical, and electrochemical properties along with its chemical reactivity. The introduction of nitrogen and sulfur that serve as electron donors or boron as an electron withdrawing group, into a carbon structure will alter its electronic states, (electro)catalytic properties, and chemical stability to oxidation and to high temperatures. The traditional methods of synthesizing heteroatom-modified carbon matrices are carried out by solid state reactions, chemical vapor deposition (CVD), and functionalization of the carbon materials. Although an impressive wide range of materials were synthesized by these methods, there are still some drawbacks that limit the progress in this field.

Herein we show a new, scalable, and easy way to synthesize heteroatom-incorporated carbon materials by means of molten-state intermediate. The molten-state intermediate is achieved by using molten precursors, polycyclic aromatic hydrocarbons as carbon source and other molten precursors for the various heteroatoms e.g. elemental sulfur or ammonia-borane complex (NH₃BH₃). These precursors once heated above their melting point form the above-mentioned molten-state intermediate which induces strong covalent/coordination bonds between the heteroatoms and the sp² carbon skeleton. This method enables the synthesis of BNCO, CS materials, transition-metal incorporated carbon/carbon-sulfur-oxide materials. The elemental composition is easily controlled within these materials (up to 30 wt.% boron, 20 wt.% sulfur, 30 wt.% nitrogen, while the transition metal ratio is kept within relevant materials) resulting in fine tuning of the materials properties. These materials show promising performance towards electrochemical OER, Na-ion and Li-ion batteries while illustrating the structure-activity relations.