The electrocatalytic hydrogen and oxygen evolution reactions are the cornerstone reactions of water electrolysis. Here, I will discuss recent advances from my group in how the electrolyte composition determines the rate of these reactions. This complex interplay between electrode and electrolyte is currently still far from being completely understood. For the hydrogen evolution reaction (HER), cations play a key role in alkaline media in promoting or inhibiting the rate-determining step of HER. For the oxygen evolution reaction (OER) on NiFe-oxyhydroxide catalysts, cations have a strong effect on the non-kinetic contribution to the OER rate, suggesting that cations influence the accessibility of the active sites inside the layered oxyhydroxide. Finally, the electrolyte composition can have a major influence on bubble dynamics at high current densities, for both reactions. If time permits, I will also include examples on the effect of different electrolyte conditions on the electrocatalytic CO2 reduction in conjuction with local pH measurements.

Carbon dioxide (CO₂) exhibits a great potential as the raw reactant for the formation of various carbon-based compounds. Using copper (Cu) as a cathode catalyst in a CO₂ electrolyser offers a unique feature of producing multi-carbon products (C₂₊-products) [1].  The scale up of the CO₂ electrolyser technology does require the catalyst activity for these products to remain stable for a high number of operational hours. Despite of this, copper experiences structural changes and , as a result, loss of catalytic activity with time towards ethylene when exposed to a negative potential [2]. Implementing periodic oxidation phases induces formation of cuprite (Cu₂O), with other works showing its benefit to the stability of CO₂ electrolysis towards C₂ products [3]. In this work, different criteria for the (electro)chemical oxidation of copper in a PEEK- flow cell as method of lengthening the catalytic activity are formulated. Using different ‘off’ potential values and different times spend at the open circuit potential (OCP) after a reduction period at 100 mA⋅cm^-2, the process of electrochemical and chemical oxidation were studied, respectively. The results show the degree of oxidation during both chemical and electrochemical oxidation to be a determining factor for lengthening the catalyst activity towards ethylene. The latter did show an oxidation period of less than 30 seconds to be sufficient to reach similar effects if an adequate off potential is implemented, whereas chemical oxidation requires 15 minutes to demonstrate the benefits on the stabilization of ethylene selectivity with time. With the oxygen reduction reaction being the cathodic reaction during the chemical oxidation at OCP, additional supply of oxygen into the catholyte’s headspace did result in an accelerated chemical oxidation, reducing the required OCP time from 15 minutes to 5 minutes. In-situ Raman spectroscopy and ex-situ SEM supported the claims made.  The gained insights were utilized to conduct a stability test, reaching 15 hours without significant selectivity loss of ethylene.

CO₂ electroreduction (CO₂RR) using renewable electricity is a versatile technology capable of replacing fossil resources in the flexible production of fuels and valuable chemicals. Among the various products generated, CO is notable because of its role in numerous industrial processes, including its application in syngas production along with H₂.

Appropriate electrolyte selection is crucial to ensure good selectivity and efficiency in the electroreduction process. Halides have emerged as compelling candidates, offering stabilizing effects on the reaction intermediates in the CO₂RR and localized pH control at the CO₂-electrode interface, preventing the formation of species that could compromise reaction selectivity, electrode stability, and recyclability. [1]

Au catalysts exhibit high CO-faradaic efficiencies and selectivity at low overpotentials; however, their widespread use is hindered by their associated high cost. Thus, bimetallic AuX alloys have been proposed. Au-Cu is particularly intriguing, as Cu is a unique metal capable of generating high-value C₁–C₄ products (e.g., CO, alcohols, and other hydrocarbons) along with the well-known favourable Cu-halide interactions in CO₂RR. [2]

Despite the apparent convergence of Au-based catalysts and halide electrolytes in CO production, few strategies have been reported for functionalizing Au-Cu alloys with halides, especially after Cu–Cl^– interactions. Although studies have been conducted on halide adsorption on Au electrodes, CO₂RR conditions are far from optimal for their application.

This work demonstrates high Faradaic efficiencies in C1 products, especially CO, using Au-Cu alloy electrodeposited onto a gas diffusion electrode with chloride as a catholyte in a CO2-flow cell. As a result, a positive effect of chloride on gold in the presence of copper was observed, which encourages further exploration of new electrode-electrolyte configurations that may, in some cases, enhance Cu performance in obtaining C1 products.

The electrochemical CO₂ reduction reaction (CO₂RR) driven by renewable electricity sources represents an attractive approach for converting CO₂ into energy-dense fuels and synthetic chemicals, promoting sustainable chemistry and carbon neutrality.¹ The reaction involves the transfer of multiple protons coupled to electrons which enables the synthesis of multiple chemicals, but up to date, controlling the reaction selectivity towards multicarbon product formation still poses challenges to be overcome. Besides controlling the reaction selectivity, another challenge is associated with suppressing the hydrogen evolution reaction (HER), which occurs in the same potential window as CO₂RR when aqueous-based electrolytes are used. While catalysts can potentially be used to control reaction selectivity, up to date, this was not been fully achieved in the CO₂RR field, where all known CO₂RR catalysts also catalyze the H₂ formation.[2]

Different strategies to increase the multicarbon formation at industrially relevant current densities (> 500 mA cm^-2) on Cu and Ni -based electrocatalysts will be discussed in the present communication. This includes synthesizing catalysts having different active centers or developing different catalyst layers in gas diffusion electrodes. The influence of the gas diffusion layer [3] and reactor design will also be highlighted. In addition, strategies to employ high-throughput experimentation for the discovery of new CO₂RR electrocatalyst materials will be presented.

Electrocatalysis is at the heart of emerging renewable energy technologies such as fuel cells, electrolyzes, and rechargeable metal-air batteries, all of which are expected to play a significant role in transitioning to a more sustainable future. Two-dimensional materials have emerged as promising electrocatalysts with a wide range of application in electrocatalysis involving oxygen, carbon and nitrogen reactions. In this talk, I will present our recent progress on atomic scale design of two-dimensional materials for various electrocatalysis reactions. More specifically, I focus on computational catalyst design for 1) 2e- oxygen reduction reaction (ORR) for hydrogen peroxide (H₂O₂) synthesis^1-4, and 2) CO₂ reduction reaction (CO₂RR)^5-7. In the first part, I show various strategies that we have applied to tune the activity and selectivity of carbon-based materials for 2e-ORR to enhance the production of H₂O₂. The main drawback of carbon-based materials is related to their limited performance under acidic conditions which is desired for storage and transportation of H₂O₂. Extensive experimental work demonstrates that the majority of carbon-based materials are highly active in alkaline conditions and moderately active in neutral conditions. I discuss the computational efforts in understanding the pH effect on the activity of carbon-based structures as well as the insight we can gain from them. In the second part, I describe how we can tune carbon-based materials and two-dimensional metal organic frameworks for CO₂RR as well as the insights we acquired from computational analysis. 

Herein we describe a novel type of hybrid material for the reduction of CO2 under high reaction rates. It consists of nanocrystalline organometallic clusters whose core comprises several covalently linked silver or copper atoms, with organic ‘ligands’ orderly distributed in the outer shell. Known as silver acetylides, these molecules involve stable alkyne-metal covalent bonds, allowing for the direct modulation of the metal clusters’ electronic properties by tailoring the chemical structure of the organic moiety. The versatility of these catalysts is further enhanced by the fact that their synthesis involves only one highly selective synthetic step from an alkyne precursor and a silver salt and can be carried out on a multigram scale without any purification step. The metal acetylides form readily from mixing aqueous and methanolic solutions of the latter precursors as highly insoluble species. Therefore, large libraries of catalysts can be synthesised from a vast selection of commercially available alkyne precursors. The catalytic properties of such entities were discovered only very recently, with only three alkynyl clusters (silver and gold) reported for the reduction of CO2 in laboratory-scale electrolysis systems. We took the field a significant leap further from reported literature studies, demonstrating the ability of alkynyl silver clusters to efficiently catalyse the CO2 reduction reaction under high reaction rates in a flow cell electrolyser. Electrolysis currents well above 200 mA/cm2, a widely accepted benchmark, were achieved with high selectivity towards CO (>95% FE) a remarkable stability

Electrocatalytic hydrogenation processes (ECH) allow the sustainable direct conversion of organic substances using electric current on a catalytically active electrode without the necessity of hydrogen gas, elevated temperatures, or pressures. In a previous project, our group developed a zero-gap electrolyzer that allowed Faraday efficiencies (FE) of 75% for the semi-hydrogenation of 2-methyl-3-butyne-2-ol (MBY) to the Vitamin E-synthon 2-methyl-3-butene-2-ol (MBE) at current densities and run times significantly surpassing those of established protocols.^[1]

Herein, we illustrate the electrochemical deposition of silver, copper and nickel on different carbon carrier materials on a time scale of 5 – 15 min per electrode in an electrochemical flow cell. Depending on the applied current density, the time of deposition and the flow rate of the metal electrolyte, entirely different morphologies, sizes and crystallinities of the metal particles were obtained featuring characteristic current efficiencies in the ECH of MBY. Among other things, this makes the configuration of this work stand out against state-of-the-art systems, in which electrode preparation is mostly carried out upon application of specifically prepared catalyst inks on a carrier material e.g. by spray coating or drop-casting, which means a significant additional time and resource expense for the whole process. Since the electrodes were applied in a zero-gap flow reactor similar to the flow cell that was used for electrode preparation, the presented electrode configuration allows the preparation and use of the materials in one process step without intermediate processing or purification.

The prepared silver-plated air-stable carbon electrodes enable the ECH of MBY at 93% current efficiency at 80 mA cm^-2. The concept features extraordinary resource efficiency, resistance towards errors in preparation and an outstanding performance of 76% FE and a cell voltage of 2.7 V at 240 mA cm^-2 current density and a loading of 0.2 mg cm^‑2, corresponding to a production rate of 1465 g_MBE g_cat^-1 h^-1. These numbers are reproducible even upon single-pass operation which is widely applied in industrial protocols. With this, it surpasses the performance of state-of-the-art electrocatalytic systems^[1,2] for MBE-generation and even approaches that of the best reported thermocatalytic ones.^[3]

Remarkably, the electrode concept is applicable to a range of 17 C-C‑, C-O- and N-O-unsaturated compounds among which seven could be converted with a current efficiency >45% with MBY, benzaldehyde, 2-butynol and nitromethane even allowing their hydrogenation in neat form without the addition of solvent or electrolyte salts.

This work provides a valuable contribution to the transfer of electrocatalytic hydrogenation processes onto an industrially relevant platform and addresses the room for improvement of established processes from a wide point of view by considering the whole electrode life cycle.

The urgent need for large-scale renewable energy storage and carbon mitigation strategies calls for efficient methods of converting carbon dioxide (CO­­₂) into valuable hydrocarbon fuels¹. Among these, methane (CH₄) holds particular promise due to its high energy density and compatibility with existing infrastructure. Electrochemical CO₂ reduction (CO2R) to CH₄ offers a direct pathway to decarbonize natural gas, but practical applications require high current densities, selectivity, and energy efficiency [1,2].

In this study, we present a novel approach to enhance CH₄ production via CO2R in aqueous bicarbonate systems [3]. Our research addresses the limitations of previous systems and introduces a paradigm shift in CO₂ electroreduction. We leverage the benefits of large-pore Cu electrodes, which facilitate the transport of dissolved CO₂ and promote efficient bicarbonate conversion into CO₂. This architectural innovation results in high local CO₂ concentrations crucial for CH₄ selectivity.

Furthermore, we introduce an in-situ Cu activation strategy achieved through alternating current operation. This activation method not only generates, but also maintains a highly selective Cu catalyst surface, favoring CH₄ production over hydrogen evolution. Our aqueous-fed system achieves remarkable CH₄ Faradaic efficiencies, exceeding 70% across a wide current density range (100–750 mA cm^-2), and maintains stability for at least 12 hours at 500 mA cm^-2.

Importantly, our system also demonstrates the highest CH₄ product concentration, compared to previous CO₂-to-CH₄ systems. These findings open new avenues for the large-scale production of CH₄ via CO2R, with implications for renewable energy storage and the reduction of greenhouse gas emissions. We believe our innovative approach paves the way for practical and sustainable CH₄ production from CO₂, contributing to the global effort to combat climate change.

In this talk, I will present some recent results from my group on CO₂ and CO electroreduction on transition metals and compare them to NO electroreduction.

First, I will show that the choice of CO₂ or CO as feedstocks for electrolysis ought to be made depending on the morphology of Cu electrodes, as the structural sensitivity of those two species is markedly different [1].

Moreover, I will discuss pathway bifurcation in the CO₂ reduction pathway to CH₄ upon hydrogenation of adsorbed CO in two different ways: from a joint experimental-computational perspective on single-crystal and polycrystalline Cu electrodes [2], and from a purely computational perspective on various transition metal electrodes [3].

Finally, I will introduce the concept of “catalytic matrix” [3, 4], a computational tool that will help me illustrate the overall similarities and differences between CO hydrogenation and NO hydrogenation on a wide number of active sites at transition metal electrodes [4, 5].

Electrolyte effect in electrochemical reduction of CO₂ on Cu electrode.

Amanda C. Garcia

a.c.garcia@uva.nl

This lecture delves into the core principles underlying the electrochemical reduction of carbon dioxide (CO₂RR) and its interaction with the hydrogen evolution reaction (HER). Our focus centers on our group's extensive exploration of CO₂RR on copper electrodes, especially in organic solvents.

Employing online gas chromatography techniques, our findings highlight the profound influence of electrode morphology and solvent composition on this reaction. Notably, in organic solvents such as acetonitrile, our in situ FTIR measurements elucidate the critical role of water content at the solid-liquid interface in shaping reaction selectivity. Moreover, we unveil that the CO₂ reduction reaction impedes HER in these conditions.

Extending prior observations in aqueous solvents, our investigation reveals the decisive impact of alkyl cation length—commonly employed as an electrolyte in organic solvents—on dictating the reaction mechanism. Specifically, our research showcases that smaller cations (TEA) promote oxalic acid formation, while the largest cation (TBA) favors carbon monoxide production.

This lecture will leverage in situ spectroscopic techniques alongside DFT calculations to elucidate the intricate mechanism behind these reactions and unravel the pivotal role of the cation in determining product distribution.

The influence of the reaction environment on the rate and selectivity of electrocatalytic reactions has received increasing attention in the last years. With that, many insights were gained on how to optimize electrolyte compositions. In practice, however, ideal conditions cannot always directly be applied due to solubility or conductivity limitations. This is the case for, e.g., multivalent cations which significantly improve the reactivity of H₂O – a key reactant in various electrocatalytic reduction and oxidation reactions. Such species are only soluble in acidic media (at pH below the ion´s pKa of hydrolysis), which limits their applicability under reducing conditions, which are often associated with an increase in local alkalinity. Therefore, new strategies are desired to ensure the presence of these reaction-boosting multivalent cations in the double layer under (local) alkaline conditions. Here, I discuss the modification of different electrocatalysts with porous amphoteric hydroxide layers. This strategy is depicted in Fig. 1, using as example the hydrogen (HER, 2H₂O + 2e^– à H₂ + 2OH^–) and oxygen (OER, 2OH⁻ → ½O₂ + H₂O + 2e⁻) evolution reactions taking place in alkaline media (0.1 M KOH), and Al(OH)₃. The Al(OH)₃ is initially insoluble, but once either HER or OER start taking place, strong alkalinization or acidification of the interface, respectively, lead to the partial dissolution of the hydroxide locally forming Al(OH)^–₄ or M³⁺ ions. Here, I present new insights on the synthesis and characterization of various of these layers and the impact they have on the rate of different reactions in which H₂O participates as a H⁺ or OH^– donor.

Water splitting in acidic media is a promising way for the production of hydrogen fuel. The limiting process of such electrochemical splitting in proton exchange membrane water electrolyzers (PEMWE) is the oxygen evolution reaction (OER). Among tested materials, Ir-based electrocatalysts currently achieve the best ratio between efficiency in the acidic environment. Despite many studies, some questions regarding the splitting mechanisms still remain open [1]. This means that, in addition to the more frequently used research techniques, it is also necessary to use other approaches. Raman spectroscopy and spectroelectrochemistry can give us additional information to support or disprove the current state-of-the-art regarding the Ir-based electrocatalyst performance.  

In this work, we compared the performance of commercial IrO₂ (i) and Ir nanoparticles (ii). Their characteristics were first studied using X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). XRD clearly revealed the presence of rutile type IrO₂ in the first sample (i) and metallic Ir in the second one (ii). For the latter sample (ii), EDS showed that some surface oxidation of Ir nanoparticles occurred which was confirmed by Raman spectroscopy through the presence of the broad bands of amorphous IrO₂. Rutile IrO₂ is characterized by four active Raman modes, which appeared in our Raman spectra of the IrO₂ sample (i) at 548 cm^-1 (E_g), 719 cm^-1 (overlapping B_2g and A_1g modes) while the low-intensity B_1g mode at 145 cm^-1 [2] could not be identified. Our in situ Raman spectroelectrochemical studies showed the presence of broad bands that were ascribed to different phases in rare previous works [3,4]. However, these works were performed in various electrolytes and conditions and, for electrochemically deposited Ir nanoparticles. Our aim is to identify and compare changes in in situ Raman spectra in both types of samples, in different acidic electrolytes (HClO₄ and H₂SO₄) and in different potential ranges. According to current results, it is expected to obtain important insights into the mechanisms of water splitting.

Spectroelectrochemistry has just recently paved its way into the studies of electrocatalysts, although being a well-established technique in the investigation of electrochromic thin film materials. Extending the potential into the OER region was shown to offer important conclusions about the oxidized states of Ni-based electrocatalysts [5]. Such experiments have not yet been reported for Ir-based electrocatalysts but have already been made in our laboratory for drop-casted Ir-based electrocatalysts during cyclovoltammetric cycling.

Carbon materials, such as graphene and carbon nanotubes (CNTs), are frequently incorporated to develop multifunctional electrocatalysts for energy conversion reactions, such as water oxidation and reduction, and oxygen reduction reactions, etc. Many studies have reported that the enhanced catalytic performance resulting from the introduction of carbon materials is primarily attributed to their conductivity, which improves charge transfer kinetics compared to pristine electrocatalysts. In this presentation, we synthesized nanosheet-shaped Ni-based catalysts on CNTs and achieved comparable or even superior catalytic performance to those of the well-develpoed noble catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Through systematic analyses and DFT calculations, we discovered that the distortion of Ni active sites induced by the CNT support is the main factor contributing to improved OER and ORR performance. Utilizing this bifunctional catalyst, we also successfully achieved Zn-air batteries with high capacity and extended cyclability. The local structural distortion induced by interfacial charge transfer contributes to tunable catalytic activity that opens an avenue for design of low-cost and multifunctional catalysts and extends its applications in the fields of clean and renewable energy.

The oxygen evolution reaction (OER) represents an important bottleneck in water electrolysis systems. Currently, one important limitation of the OER is that the best catalysts for efficient (active and stable) operation in acidic media rely on Iridium (Ir) oxide – a rare, scarce metal. Alternative ruthenium (Ru) based systems have the prospect of high intrinsic activity, resulting from the optimum binding energy with the reaction intermediate [1], but suffer from limited stability compared to Ir catalysts.

Identifying the origin of stability limitations in Ru-based systems and using this information to improve the activity and stability performance is thus of interest. Strategies to do so comprise lowering the oxidation state of Ru centres and thereby lowering the dissolution chances [2-5]. To favour the OER, the active sites can be structurally and (or) electronically modified by the dopants.

In our work, we explore the role of metal dopants introduced in the Ruthenium oxide structure through a sol-gel synthesis protocol. We find, for selected metal dopants, a pre-catalyst reconstruction that favours the exposure of active facets with a different oxide network compared to Ru control samples, at increasing current densities. This leads to improved OER activity and stability metrics: the reconstructed catalysts show an overpotential of 171 mV at 10 mAcm^-2 and 306 mV and 100 mAcm^-2, versus a reversible hydrogen electrode. X-Ray Diffraction and Raman spectroscopy informs on the differences in the pre-catalyst and constant current traces show the effect of reconstruction on performance.

Catalytic conversion of solar energy into energy vectors is prospected to play a key role in the decarbonization of future societies. The process consists in the use of an intermittent renewable energy source to catalytically synthetize added-value molecules, which can later be used as fuels. Thus, rendering the stored renewable energy available on all occasion and available on demand. The large availability and high gravimetric energy density of hydrogen make it a promising molecule to be used as a chemical storage of renewable energy. Indeed, hydrogen can be obtained as the product of the Hydrogen Evolution Reaction (HER), taking place at the cathode of a water splitting electrochemical cell. Hydrogen production is not the only energy-relevant electrochemical cathodic process that can be exploited in the optic of carbon emissions: CO₂ can also be reduced into e-fuels or added value chemicals through a series of cathodic reactions (CO2RR). At the present technological state, the main bottleneck that hinders a faster electrochemical production of some of the mentioned energy vectors is the slow kinetics of the Oxygen Evolution Reaction (OER). This reaction takes place on the anode of an electrochemical cell and provides the electrons required by HER or CO2RR.

Ni and Ni-functionalized materials have been showing good results as catalysts for OER [1,2], acting to increase the kinetics of the anodic processes. The Ni nanostructures presented in this work are produced via the organometallic approach [3]. This synthetic method consists in the decomposition of an organometallic precursor of the metal under mild reducing conditions and in the presence of a stabilizing agent (i.e., a ligand). This synthetic approach allows great control on the surface properties of the final product as well as facilitating the functionalization and the characterization of the produced catalyst (since it avoids the presence of possible contaminants). This communication will center on the synthesis, characterization, and testing of a family of nanostructured Ni catalysts for OER. The advantages provided by the unique synthetic method, yielding fast and durable systems, will be related to the catalyst morphology and surface-functionalization [4]. Moreover, some of the reported structures are expected to act as catalysts also for CO2RR [5]. If proved, this might open the way to the use of just a single catalyst in both compartments of an electrochemical cell for e-fuels production.

The electrification of chemical processes for the sustainable production of fuels and chemicals has garnered substantial interest in recent years. Three particularly intriguing opportunities are green H2 production by water electrolysis, the electrochemical reduction of CO2 to carbon-based fuels and chemicals, as well as ammonia production through electrochemical N2 conversion. In all of these cases, understanding interfaces with greater molecular detail is key to advancing activity, selectivity, and durability, important metrics that need to be improved for broader-scale implementation and commercialization of these technologies. This paper will describe efforts to design and develop new methods to understand relevant interfaces in these reactions, with a focus on in-situ, operando, and/or on-line techniques. This includes attenuated total reflection Fourier transform infrared absorption spectroscopy (ATR-SEIRAS), X-ray Absorption Spectroscopy (XAS), and inductively coupled plasma mass spectrometry (ICP-MS). The focus is to understand molecular-level processes at interfaces that govern performance and durability, with examples ranging from model surfaces to applied, high-performance systems.

Transitioning from fossil to renewable resources is crucial for advancing clean energy conversion and fostering a sustainable chemical industry. The current dependence on fossil resources for production of carbon-based platform chemicals poses a significant challenge. Utilizing inedible biomass as a renewable carbon source is a promising alternative. Electrochemistry offers an innovative route to transform biomass into valuable chemical building blocks, leveraging green chemistry principles such as compatibility with aqueous media, generation of benign redox environments, and operability under near-ambient conditions. Despite these advantages, the electrochemical valorisation of many biomass-derived chemicals remains largely unexplored, particularly in understanding electrocatalytic interfaces for these reactions. This gap presents a significant opportunity for pioneering advances in sustainable chemical (electro)synthesis.

In this contribution, I will showcase our research on the electrocatalytic conversion of a series of biomass-derived organic acids.[1-3] Our investigation bridges fundamental aspects from model compounds to practical applications with industrial biomass streams. I will discuss the multifaceted challenges and prospects of electrocatalytic conversion of these chemicals, including revealing structure-activity relationships, and proposing strategies to enhance activity, counteract catalyst deactivation and enhance reaction selectivity. The opportunities to integrate paired biomass electrolysis for energy-efficient green hydrogen production will also be considered. Our work provides further understanding on the sustainable electrosynthesis of chemicals from renewable biomass resources, opening new avenues for new developments in this field.

The global transition to sustainable energy sources and the evolution toward a hydrogen-based economy demand energy formats that enable prolonged storage and efficient transportation from remote, renewable energy-rich locations. Liquefied energy forms, notably ammonia (NH₃), are gaining favor as viable alternatives, serving not only as a prominent energy carrier but also playing a crucial role as feedstock for the chemical and fertilizer industries.

In this context, highly efficient nitrate electroreduction (NO₃^-RR) emerges as a pivotal process for sustainable NH3 production, promising to overcome limitations associated with the current Haber-Bosch process. However, existing electrocatalysts face significant drawbacks in productivity yield, energy efficiency, and stability, especially under industrial conditions.

The NO₃^-RR process involves an eight-electron transfer assisted by protons, generating multiple intermediates that can diminish overall efficiency, particularly when NH₃ is the desired end product. Several studies recognize the reduction of NO₃^- to nitrite (NO₂^-) as the rate-determining step (RDE), with subsequent chemical and electrochemical steps occurring after the formation of NO₂^-. Consequently, at low overpotentials with negligible competition from the Hydrogen Evolution Reaction (HER), the deoxygenation of adsorbed NO₂^- determines the overall NO₃^-RR, accentuating the importance of targeting this step to maximize NH₃ generation. The accumulation of NO₂^- intermediate byproducts in the electrolyte necessitates the simultaneous acceleration of NO₃^-RR and NO₂^-RR to NH₃, presenting a challenging yet promising approach for efficient ammonia generation.

This study introduces a tandem NO₃^-RR process, involving sequential electrochemical processes converting NO₃^- to NO₂^- and then NO₂^- to NH₃. An employed composite electrocatalyst of Titanium Dioxide with oxygen vacancies (TiO_2-x) deposited on a Copper oxide (I)-copper (Cu₂O-Cu) surface, coupled with an optimized flow-cell configuration, produces compelling results toward NH₃: a Faradaic Efficiency (FE_NH3) of 97%, selectivity (SE_NH3) of 80%, and a productivity yield of 0.45 mmol h^-1 cm^-2. The cooperative synergy of intrinsic properties of the electrode composition and cell configuration enables high Half-Cell (EE_NH3) and full-cell (EE_CELL) energy efficiencies (52% and 43%, respectively).

In summary, our tandem NO₃^-RR process represents a significant advancement in addressing the challenges of sustainable ammonia production, providing a promising and efficient approach for environmentally friendly energy applications.

The synthesis of ammonia for fertilizer use has the highest energy consumption (2.5 EJ / year) and carbon emissions (340 Mt CO2 eq/year) of any commodity chemical. The high environmental impact is attributed to the use of steam reforming to produce hydrogen, the production scale (200 MMtons NH3/year), and the energy intensity required to maintain reactor operating conditions (~100 bar and ~700 K). Interestingly, most of this ammonia is used for the production of carbon-nitrogen-based fertilizer (urea). The direct production of ammonia and/or urea using electrons is of growing interest to decarbonize fertilizer production. The chief challenge with these approaches remains the low catalytic selectivity. Low selectivity is attributed often to the the more facile hydrogen evolution reaction. However, during reactions with multiple reactants (co-reactants), low selectivity is also due to an increase in products that can form on the catalyst. For instance, during electrocatalytic urea synthesis, dinitrogen gas, nitrate, and carbon dioxide often serve as reactants, while ammonia, nitrite, and a range of C₁₊ and C₂₊ carbon products can be formed. Here, we aim to discuss recent progress made in understanding the role co-reactants play during the production of nitrogen-based fertilizers (e.g. ammonia and urea). We will highlight through bulk product analyses and in situ spectroscopic investigations the critical adsorbates that inhibit and augment the production of urea.

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 not only in CO₂ conversion in the use of this molecule as a building block. This entails the co-electrolysis of CO₂ with additional small molecule reactants (N₂, 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.

A (very) short introduction to the RSC’s portfolio of journals covering the breadth of energy, materials, nanoscience and catalysis.

Low-temperature electrochemical CO₂ reduction (ECO₂R) is proven to be one of several promising strategies to valorise CO₂ through its conversion into value-added products and fuels. In fact, it is the only alternative for the direct conversion of CO₂ into ethylene, with Cu being the only metal exhibiting any selectivity and activity towards the conversion of CO₂ to C₂ products. However, developing functional materials as electrocatalysts and electrodes is imperative to achieve industrially relevant performances and efficiencies. In this sense, besides the necessary improvements in terms of decreased energy consumption at high current densities, it is important to improve the faradaic efficiencies towards desired carbon products, while hindering the competitive hydrogen evolution reaction (HER). Gas-diffusion electrodes (GDE) based on carbon paper and cloth are the standard approach used in ECO₂R; however, during operation, the surface properties (e.g. wettability) of such carbon-based GDEs might change, ultimately favouring the HER and, thus, affecting the efficiency of the process. As alternative, few examples proposing the use of PTFE-based porous structures on which metallic Cu layers are used as both conductive support and catalyst[1], have demonstrated to be a promising approach to avoid the use of carbon-based electrodes. In the context of SolDAC HE project, we have developed a systematic study on the deposition conditions of sputtered Cu on PTFE structures. Therefore, we have observed that these physical features have a significant effect not only on the electrical conductivity of the electrodes, but also on the ECO₂R performance towards specific products. As observed, different pressure conditions during sputtering modify the texture of the surface and induce crack formation. This variation leads to different operation cathode potentials, that can decrease up to 400 mV at 200 mA·cm^-2 in the electrodes with smoother surfaces, while the product distribution is also significantly affected by the current density on electrodes with varied physical properties. Faradaic efficiencies to ethylene >70% are attained with as-prepared GDEs based on Cu-PTFE, reaching excellent performance in electrodes of geometric areas of 10 cm², after tunning the interface by modifying the electrode surface.

It is well known that climate change is one of the main challenges of our generation. The large CO₂ emissions generated by anthropogenic activities are the main contributor to the so-called greenhouse effect. Therefore, the decarbonisation of industries and energy sources is of utmost importance. In this context, the electrochemical CO₂ reduction reaction (CO₂RR) is a promising way of reutilising the emitted CO₂ to form value-added chemicals. Amongst the broad spectrum of species that can be obtained, CO is arguably one of the most industrially relevant products.[1] In addition, CO is a more reactive molecule than CO₂ and can therefore be activated to form more reduced carbon products, such as formate or ethanol. Hence, it can be employed in a tandem-catalyst system to convert CO₂ into C₂₊ species in a more controlled manner.[2] Regarding the selective conversion of CO₂ into CO, there are only a few candidates. Au-based catalysts, and in particular Au nanoparticles (NPs), have been shown to achieve high efficiencies and current densities at low overpotentials for this reaction. Furthermore, it has been demonstrated in a number of studies how the functionalisation of the surface of these NPs with different ligands, such as amines or thiols, can enhance the activity and selectivity of Au catalysts for the CO₂RR.[3] In this work, ligand-capped Au NPs have been synthesised by a novel organometallic approach using hexadecylamine (HDA) and tetradecanethiol (TDT) as stabilisers. The NPs obtained with both ligands present the same size around 1 nm and show no significant aggregation in TEM micrographs. However, electrochemical studies showed that the TDT-capped Au NPs had a poor catalytic performance in comparison with its HDA-capped analogue. Interestingly, these two systems of identical size, showed a shift in their plasmon resonance peaks as seen by in the UV-vis spectroscopy. Hence, this unusual behaviour was explored in order to get to the root of the surprising differences in their catalytic activities.

To date 80% of worldwide energy is derived from fossil fuels, which is unsustainable in the mid-long term. Solar fuels are promising candidates for replacing fossil fuels as energy sources.[1] However, its renewable and clean generation is still a great challenge. A particularly attractive solution is artificial photosynthesis, which follows the blueprint of the photosynthetic processes found in plants or phototrophic microorganisms in which carbohydrates are made from H2O and CO2 using solar energy. Various reactions are under study, including water splitting, where water is converted into hydrogen fuel and oxygen, and CO2 reduction, where CO2 and electrons are converted into carbon-based fuels (e.g.CH4, CH3OH, etc.) and/or useful chemical feedstocks (e.g. CO, ethylene, etc.). However, the practical development of these technologies is still hampered by the lack of selective, cost-efficient catalysts able to speed up the redox areactions involved, namely oxygen evolution, CO2 reduction and hydrogen evolution reactions (OER, CO2RR and HER, respectively).

Both molecular and metal/metal-oxide species are plausible candidates for efficiently catalyze these processes. If durability and the attainment of high current densities are the main challenge for molecular HER/OER/CO2RR catalysts, slow reaction rates are common when their counterparts at the nanoscale are employed. Furthermore, the reduced mechanistic knowledge and lack of well-controlled synthetic strategies to fine-tune these species prevents the rational development of more selective nanocatalysts for these transformations.[2]

This contribution deals with the work carried out in our laboratories to unravel the key factors able to change these last general trends by means of tunable surface-functionalized nanocatalysts.[3] This strategy allowed obtaining stable and efficient OER (photo)catalysts based on 1st-row transition metal oxide species,[4],[5] fast and rugged Ru-based (photo)cathodes[6],[7],[8],[9] superior to state-of-the-art Pt/C for HER, and selective photocatalyst for the CO2RR.[10]

There is a burgeoning interest in the development of a green method of ammonia synthesis; ammonia, already critical for fertilisers in the agricultural industry, is also being touted as a possible future energy vector or carbon-free fuel. The current method of production - the Haber Bosch process - is environmentally damaging and energy intensive but to date no viable alternative has been demonstrated. An electrochemical method operating under ambient conditions would be particularly attractive, as it would enable ammonia to be produced on a decentralised basis on-site and on-demand.

Thus far, amongst solid electrodes, only lithium based electrodes in organic electrolytes can unequivocally reduce nitrogen to ammonia.Even so, at present, the lithium based system is too inefficient for practical uses; moreover, it is highly unstable.

To investigate this reaction, we use a combination of electrochemical experiments, cryo-microscopy, infrared spectroscopy, electrochemistry mass spectrometry, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and density functional theory. By drawing from the adjacent fields of enzymatic nitrogen reduction and battery science, I will aim to build a holistic picture of the factors controlling nitrogen reduction.

In the current contribution, I will explore (a) the underlying reasons why lithium can reduce nitrogen to ammonia and (b) how to optimise lithium mediated nitrogen reduction and (c) propose new avenues towards going beyond lithium in electrochemical nitrogen fixation.

Water electrolysis and carbon dioxide electroreduction are examples of electrochemical technologies with promise to aid in the energy transition, for example for the seasonal storage of renewable electricity, or carbon sequestration, thereby aiding in the abatement of anthropogenic climate change. Such reactions are often even more difficult to characterize “at work” with spectroscopy than traditional thermo- or heterogeneous catalysis[1-3], as they bring at least one additional complicating variable; the electrolyte which, particularly for reactions in aqueous environments dramatically attenuates the electromagnetic radiation with which we set out to probe the reaction. Ideally, one would be able to speciate the kinetic regime where e.g., charge-transfer, and adsorption/desorption reactions happen, and be able to separate (speciate) these events from for example those which relate to capacitance, e.g., charging and discharging of the electric double layer, and mass transfer phenomena all happening on a different time scale. To fully understand the morphology of the electrode, the effect of local pH gradient, and the resistance of the electrolyte, one should develop a method able to combine the study of both the electrode, and the electrolyte and reactants preferably simultaneously. Through the development of a methodology that includes bespoke reactor and setup design, along with potential-modulated excitation experimentation, operando high time resolution FT-IR and operando sub-second time resolution X-ray absorption spectroscopy (quick-XAS), and supervised regression, we are able to speciate signals from the diffusion, and Helmholtz layers, to the catalyst surface, and reaction intermediates of electrocatalytic reactions in aqueous media. We thereby establish, for example, structure-performance relationships of electrocatalytic oxidation and reduction reactions (e.g., ammonia, and urea oxidation, oxygen evolution reaction and CO₂ reduction) over several different metals and electrode geometries.

This supervised-pulsed-speciation operando spectroscopic approach is a powerful tool to overcome some of the common issues dealt with in operando spectroscopy of electrocatalysis, such as weak reaction intermediate signals which are clouded by electrolyte rearrangement in for example double layer formation, thereby elucidating several details of mechanisms not yet described in literature, such as the contribution of ice-like water layers, and nanoparticle geometry-dependent adsorption events.

A promising approach to store energy is the use of excess electricity to drive the production of fuels and chemicals in electrochemical reactors. However, the lack of understanding of the relation between transport phenomena (e.g. mass, heat, charge), intrinsic kinetics and electrocatalytic performance is currently limiting the scale-up of electrocatalytic technologies particularly for transformations where transport phenomena play a role in determining product selectivity and production rate [1],[2].

In this presentation, I will discuss our novel approach of combining reactors design, multi-scale modeling and dimensionless analysis to understand and decouple mass transfer effects and intrinsic electrode kinetics particularly for transformations that involve dissolved gas substrates such as CO₂ and diluted protons in near neutral pH.
In this talk, the development of a multi-scale first-principles reaction-transport model is presented for the electrochemical reduction of CO₂ to fuels and chemicals on polycrystalline copper electrodes. The model utilizes a continuous stirred-tank reactor (CSTR)-volume approximation that captures the relative timescales for mesoscale stochastic processes at the electrode/electrolyte interface that determine product selectivity. The model is built starting from a large experimental dataset obtained under a broad range of well-defined transport regimes in a gastight rotating cylinder electrode cell[1]. Product distributions under different conditions of transport, applied potential, bulk electrolyte concentration, temperature, and catalyst porosity are rationalized by introducing dimensionless numbers that reduce complexity and capture relative timescales for mesoscopic and microscopic dynamics of electrocatalytic reactions on copper electrodes. This work demonstrates that one CO₂ reduction mechanism can explain differences in selectivity reported for copper-based electrocatalysts when mass transport, concentration polarization effects, and primary and secondary current distributions are taken into account. The reaction-transport model presented here should enable the rational design of CO₂ electrolyzers.

Electrochemical reduction of CO2 presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. Novel catalyst screening for this electrochemical process is crucial in improving selectivity, stability and required mass loadings. To date, however, catalyst testing occurs mainly on a 1-by-1 basis that strains quick identification of potential candidates. While advances in combinatorial screening have been presented, most of these rely on system designs that do not resemble representative conditions in lab-scale or industrial scales. To bridge this gap in benchmarking, we developed a lab-scale electrolyzer to screen 16 combinations of catalysts at the same time, using infrared thermography as the proxy for electrochemical activity. To showcase the effectivity of this method, we perform test runs on blank ink and sputtered catalyst samples, and subsequently analyse the spatial effects in our system. Subsequently, we study different catalyst loadings of copper for hydrocarbon production. Finally, we compare different catalyst precursors for the catalyst particles. The method shows an improved accuracy over existing solutions while employing a much more adequate system architecture.

Tailoring the properties of the catalytic layer (CL) alongside its architecture is a key development towards ensuring both improve efficiency and selectivity for CO₂ electrolyzers.  Traditionally, CLs for the CO₂R consist of a single binder-material or a combination of them overtaking both the ion-conductance and maintenance of a hydrophobic environment.^{[1], [2], [3]}

We herein decoupled these processes into two individual, stacked catalyst-containing layers. Specifically, a hydrophobic catalytic layer was herein placed on the GDL aiming to improve water management within the CL during CO₂R in zero-gap electrolyzers, while a second catalytic layer bound by an ion-conducting binder allows for the conduction of OH^- and HCO₃^-/CO₃^2- during CO₂R, improving both the ionic conductivity between the GDE and AEM as well as the mechanical adhesion between the different interfaces. Notably, we present the complete stepwise CL-optimization pathway, regarding both the single and segmented-CLs towards the CO₂-CO conversion at current densities ≥ 300 mA cm^‑2, highlighting the role of the operational parameters regarding scalability in different cell sizes and long-term stability > 100 h.

The oxygen evolution reaction (OER) is the predominant overall reaction bottleneck in water electrolysis towards achieving the large-scale production of sustainable H2. A proton exchange membrane-based water electrolyzer (PEMWE) shows advantages in operating at higher current densities, low H2 cross-over, and improved energy efficiency; over diaphragm and anion transport-based water electrolysers [1]. However, today´s OER catalysts in acid rely on rare and expensive critical raw materials such as Ir, Pt, or Ru. This limits the broad-scale implementation of PEMWE technology. Hence, the development of new platinum-group metal (PGM)-free electrocatalysts for the OER that combine efficiency and robustness in acidic conditions is paramount for clean H2 production from water [2–3]. We present new Co-based anode catalysts that achieve high activity and stable operation. Our synthetic strategy triggers a structural reconstruction of Co-based oxides that enables a different OER pathway by controlling the local oxide structure. The catalyst achieves 1.8 A‧cm−2 of current density at 2.0 V in PEMWE system at 80˚C using milli-Q water as electrolyte. It exhibited 278 h and 250 h of durability at 0.2 and 1.0 A‧cm−2 of current density, respectively, in industrial relevant conditions. Our study outperforms the durability of benchmark non-PGM catalysts over eight-times in the PEMWE system [2–3].

Electrochemical carbon dioxide (CO₂) conversion to multi-carbon (C₂₊) gas/liquid chemicals, such as ethylene (C₂H₄), offers a promising solution for the long-term and large-scale storage of sustainable energy. The viability of this approach requires further progress in terms of combined high selectivity at a high current density, and carbon efficiency. Today, this is challenged by the favorable conversion of CO₂ into carbonates in the OH^- rich environments associated to high current density operation. Here, we present an heterostructured core-shell structured Cu-based catalyst that enables control over the local OH^- and carbonate balance, and improved *CO and *CO2^·- coverage – as revealed by a suite operando Raman spectroscopy, pre and postmortem characterization, and electrochemical studies. The resulting gas diffusion cathode electrodes, implemented in a bipolar membrane configuration, achieve a 40% Faradic Efficiency towards C₂H₄ at a 1-A×cm^-2 current density. The robustness of the catalyst is proved by 30 hours continuous electrochemical stability measurement performance.