Obtaining transmission electron microscopy (TEM) micrographs of nanostructured electrocatalysts is a well-established characterization practice known for decades. It provides local nanoscale morphological, structural and recently also compositional information about the studied materials. Atomically resolved images provide even more insights like strain maps, locations of twin boundaries, surface facets, etc. These are all governing electrocatalyst performance via structure-function relationships.

In my talk, I will introduce a method and a concept of identical location transmission electron microscopy (IL-TEM) [1] and how it can help us gain insights into structure-stability relationships of the studied electrocatalysts. I will argue that IL-TEM provides us with an objective evaluation and certainty of observed events. Compared to random ex-situ TEM there is at least one crucial and obvious limitation, namely no information about the exact history of the observed location before the electrochemical treatment. Thus, in ex-situ microscopy, only general statistical descriptive insights are possible by evaluating numerous locations, which are always subjectively chosen by the operator.

Secondly, based on precise atomically resolved TEM data, Kinetic Monte Carlo (KMC) simulations can provide further feedback into the physical parameters governing electrochemically induced structural dynamics. [2] A few examples of the IL-TEM approach will be given on the topic of low-temperature fuel cell and electrolyzer catalysts. [3, 4]

Furthermore, advancements in the development of the modern TEM detectors (e.g., 4D STEM) even more information can be gained providing large amounts of data sets for the processing and simulations. In order to access relevant information in an objective and accurate manner, advanced data processing algorithms to analyze TEM images need to be used. With this, also the opportunity to use machine learning algorithms becomes viable. In perspective, much is still left to be explored in the field of nanoparticulate metallic electrocatalysts’ structure-stability understanding via high-resolution IL-TEM and data processing.

The electrochemical reduction of carbon dioxide (CO₂ER) offers a sustainable approach for CO₂ reutilization and conversion into added value chemicals. A wide variety of products can be formed during CO₂ER such as formate, CO, hydrocarbons and alcohols and therefore tuning the selectivity of CO₂ER catalysts remains a major challenge in the field.

The initial reduction of CO₂ (2e-) can yield formate or CO. While the former is commonly accepted as a terminal product which can’t be further reduced, CO has been demonstrated to be a key intermediate in the formation of higher reduction products ( >2e-) such as hydrocarbons and alcohols.^[1] The CO₂ and CO binding strength on the metal surface are key factors determining the selectivity.^[2] Post transition metals like Sn, In, Ga have weak interaction with CO₂ and are known to favor formate production.^[3–5] Au and Ag that adsorb CO weakly release it as final product. Pt, Ni, Fe and Co that bind CO too strongly are poisoned and unable to further reduce it, suppressing CO₂R and favoring HER. Cu stands out as the only metallic surface characterized by an intermediate CO binding strength that favors further reduction to hydrocarbons or alcohols. Bimetallic catalysts offer possible synergetic effects among different metals to yield optimal binding of CO as key intermediate and have been demonstrated as an approach for tuning selectivity in Cu based catalysts ^[6,7]

Here we present the screening of bimetallic composites as CO₂ER electrocatalysts using a facile synthesis by spin coating of metal precursors in solution to form mixed oxides (M_AM_BOx) thin films. We focus on combining early transition metals traditionally known to bind CO strongly and favor HER (M_A=Fe, Ni or Co) with post-transition metals (M_B= In, Sn or Ga), known to suppress HER. The influence of metal composition on CO₂ER selectivity will be discussed, along with the structural changes observed in the composites during in situ reduction

Photoelectrochemical cells (PECs) have been developed as environmentally friendly systems that can directly utilize photogenerated electron-hole pairs for water splitting, fuel production, conversion of carbon dioxide, and pollutant degradation. Most reports on the photocatalytic or PEC hydrogen (H2) evolution via water splitting have focused on the H2 reduction half-reaction by generating on the photoanode a non-valuable oxygen or using sacrificial agents to consume the generated h+, resulting in a a significant waste of energy. Lately, much effort is invested into the synthesis of valuable chemicals on the photoanode while retaining the production of H2 on the cathode.

Over the past few years, polymeric carbon nitrides (CN) attract widespread attention due to their outstanding electronic properties, which have been exploited in various applications, including photo- and electro-catalysis, heterogeneous catalysis, CO2 reduction, water splitting, light-emitting diodes, and PV cells. CN comprises only carbon and nitrogen, and it can be synthesized by several routes. Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation (up to 500 °C), make it a very attractive material for photoelectrochemical applications. However, only few reports regarded CN utilization in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and our lack of basic understanding of the intrinsic layer properties of CN.

This talk will introduce new approaches to grow CN layers with altered properties on conductive substrates for photoelectrochemical applications. The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed. I will show the utilization of PEC with a CN-based photoanode as a stable and efficient platform for the oxidation of organic molecules to added-value chemicals, with hydrogen co-production. The second part of the talk will be focused on the electrocatalytic oxidative upgrading of organic molecules by NiFe-oxide into valuable chemicals.

Recent developments in electrocatalyst design for carbon dioxide conversion are revealing that various design principles -- such as catalysts based on metal oxides, doped metals or metal alloys, and metal atoms in molecular coordination environments -- demonstrate behaviors which differ from their simple metal counterparts, revealing strategies toward enhancing selectivity toward high-value products while suppressing undesired ones. Continued rational development of catalysts demands that we have a detailed understanding of the structure-function relationships which dictate selectivity. However, under the harsh reaction conditions of CO₂ reduction (e.g. highly negative potential, local pH extremes) many of these catalysts are prone to significant structure changes, making it difficult to understand the true catalytically active form of the electrode materials. "Post mortem" analyses often fail to accurately represent the active form of catalysts, so methods are demanded which are capable of examining the electrode during operation, e.g. in situ or operando.

X-ray absorption spectroscopy (XAS) techniques can be uniquely powerful in investigating electrochemical systems under operating conditions. The high energies of X-ray photons can enable them to be used under ambient conditions and to pass through liquid electrolyte. With a tunable energy source (e.g. synchrotron), different elements can be selectively probed due to their distinct absorption edges. A wide range of information can be revealed using X-ray spectroscopy methods, including composition, oxidation states, and local coordination environment. But in situ XAS is usually bulk sensitive, whereas catalysis occurs at surfaces, so complimentary surface-sensitive methods such as X-ray photoelectron spectroscopy (XPS) are valuable. When conducted using "quasi in situ" methods, XPS can provide a good compromise between surface sensitivity and in situ conditions. Performing both XAS and XPS allows one to gain a detailed understanding of dynamic electrocatalysts. In this talk I will explain the approaches we use for both, including their pros and cons, in the framework of our study on Cu-Sn catalysts[1] with compositions tunable to achieve selective CO₂ conversion to either carbon monoxide or formate.

Reconstruction of Copper Nanoparticles at Electrochemical CO₂ Reduction Conditions: Identical Location Scanning Electron Microscopy (IL-SEM) Study

Electrochemical reduction of CO₂ (ERC) comes to the fore as one of the perspective ways to convert CO₂ to chemical fuels and other energy-dense products, ideally powered by renewable electricity. Copper is the only monometallic catalyst that can produce hydrocarbons and alcohols in decent amounts.^[1] Overpotential, selectivity, activity and stability are figures of merit that should be considered for evaluation of any given catalyst for ERC reaction. Nevertheless, up to date, the structural stability has been at least studied parameter and to bring the ERC process to an industrially relevant level, the stability of copper-based catalysts must be more scrutinized.^[2] Since nanoscale electrocatalysts' activity and selectivity are highly affected by the structural changes via so-called structure-property relationships, understanding the phenomenon and the development of approaches to control it is of paramount importance.

Among the various techniques of synthesis of copper-based catalysts for ERC, electrodeposition stood out as a generally inexpensive, simple and versatile method for obtaining copper nanostructured materials. The stability of pulse-electrodeposited copper nanoparticles under relevant ERC conditions tracked with identical location scanning electron microscopy (IL-SEM) method will be discussed. This approach provides direct evidence of the history of the tracked changes to the observed Cu nanoparticles. With this objective information, we could explain the observed structural changes with two separate electrochemical processes occurring one after another, namely copper dissolution and subsequent redeposition of the dissolved copper species in a form of new smaller Cu fragments.^[3]

In previous research[1] it was found that a tandem catalyst, consisting of spherical Ag nanospheres combined with Cu(111)-faceted nano octahedra, shows a significantly enhanced selectivity for ethanol compared to pure Cu(111)-faceted nanoparticles. More recently[2,3], we investigated the facet-dependence of this selectivity change by evaluating the products and the reaction intermediate energy landscape of the CO₂ reduction reaction on cubic Cu(100)-faceted nano particles. We find, experimentally, that the nano cubes show an even higher selectivity towards ethanol than the nano octahedra. Furthermore, using density functional theory (DFT), we show that the edges of the nano cubes are the active sites for the ethanol formation. Based on these findings we construct a semi-empirical model that allows us to map the product selectivity as a function of the size of the nano cubes. We then compare these predictions to the experimental size-dependent product selectivity results, and we find a strong agreement for the measured activities and the theoretical predictions.

Computational models of electrocatalytic reactions based on the computational hydrogen electrode [1] have greatly contributed to the discovery and enhancement of catalysts for numerous reactions [2]. Because of its intrinsic complexity, the CO₂ reduction reaction (CO₂RR) is, so far, a remarkable exception to the rule [3]. The interplay of several factors such as electrode morphology, local and bulk pH, electrolyte effects, mass transport, etc. make it difficult for CO₂RR computational models to be simultaneously predictive yet affordable [4, 5].

Although the shortcomings are usually ascribed to the disregard of kinetics in CHE-based models, in this talk I will mention two thermodynamic factors that also jeopardize their accuracy: (I) the lack or insufficient incorporation of water-adsorbate interactions for the CO₂RR intermediates, and (II) the presence of systematic errors in the gas-phase molecules calculated with DFT. I will show that relatively inexpensive solutions to these two problems exist that lead to better quantitative agreement with experiments [6, 7].

Time permitting, I will show that gas-phase errors are also significant for several other reactions but can be swiftly corrected [8].

References

[1] J. K. Nørskov, J. Rossmeisl, A. Logadottir, L. R. K. J. Lindqvist, J. R. Kitchin, T. Bligaard, H. Jonsson, J. Phys. Chem. B 108 (2004) 17886-17892.

[2] Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov, T. F. Jaramillo, Science 355 (2017) eaad4998.

[3] Z. P. Jovanov, H. A. Hansen, A. S. Varela, P. Malacrida, A. A. Peterson, J. K. Nørskov, I. E. L. Stephens, I. Chorkendorff, J. Catal. 343 (2016), 215-231.

[4] S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K Nørskov, T. F. Jaramillo, I. Chorkendorff, Chem. Rev 119 (2019) 7610-7672.

[5] Y. Y. Birdja, E. Pérez-Gallent, M. C. Figueiredo, A. J. Göttle, F. Calle-Vallejo, M. T. M. Koper, Nat. Energy 4 (2019) 732-745.

[6] L. P. Granda-Marulanda, A. Rendón-Calle, S. Builes, F. Illas, M. T. M. Koper, F. Calle-Vallejo, ACS Catal. 10 (2020) 6900-6907.

[7] A. Rendón-Calle, S. Builes, F. Calle-Vallejo, Appl. Catal., B 276 (2020) 119147.

[8] R. Urrego-Ortiz, S. Builes, F. Calle-Vallejo, ChemCatChem 13 (2021) 2508-2516.

Natural enzymes present within their structure active centres composed of earth-abundant metals in atomic proximity. Such active sites, dual atom catalysts, display a unique efficiency in catalytic processes such as the nitrogen conversion to ammonia, the production of ethylene through C-C coupling, or the oxygen reduction reaction in fuel cells amongst others.[1,2] The high catalytic activity of dual atom catalysts arises from the different binding mode of reactant molecules to that of metal foils and single atom catalysts, which allows to break transition scaling relationships.[3] Nevertheless, the synthesis of this kind of materials, as well as their thorough characterization is highly challenging owing to the trend to aggregation of isolated metallic moieties. In this work we show a general approach to fabricate bioinspired Fe dual atom catalysts in a nitrogen doped carbon support and its application as electrocatalyst in the oxygen reduction reaction. The two-step procedure leads to well defined Fe-based dimers which were characterized by means of X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy amongst others, and displays high catalytic performance, opening the gate towards the rational design of bioinspired catalysts for energy-related applications.

Machine learning (ML) has proven a powerful tool for accelerating the computational characterization of energy materials. There is a growing number of case studies identifying descriptors of catalytic performance using ML instead of physical intuition. ML is ideally suited for the pattern detection in large uniform data sets, but consistent experimental data sets on catalyst studies are often small. Here we demonstrate how a combination of machine learning and first-principles calculations can be used to extract knowledge from a small set of experimental data.¹ The approach is based on combining a complex ML model trained on a computational library of transition-state energies with simple linear regression models of experimental catalytic activities and selectivities. Using the combined model, we identify the key C-C bond-scission reactions involved in ethanol reforming and perform a computational screening for ethanol reforming on monolayer bimetallic catalysts with architectures TM-Pt-Pt(111) and Pt-TM-Pt(111) (TM = 3d transition metals). The model also predicts four promising catalyst compositions for future experimental studies. The approach is not limited to ethanol reforming but is of general use for the interpretation of experimental observations as well as for the computational discovery of catalytic materials.²  All data and models are made publicly available. To promote Open Science, we also formulated guidelines for the publication of ML models for chemistry that aim at transparency and reproducibility.³

In recent years, there is a growing interest in the incorporation of Metal-Organic Frameworks (MOFs) based thin films into electrochemical energy conversion schemes. In principle, MOF-based electrocatalytic systems hold several key virtues, such as the ability to immobilize unparalleled amount of catalytic sites; intrinsic inclusion of mass-transport channels; the ability to add molecular shuttles to deliver redox equivalents to and from the MOF-tethered catalytic sites; and finally, much like in catalytic enzymes, MOFs offer the possibility to modulate the catalyst’s secondary chemical environment. Indeed, over the last years several reports have demonstrated the concept of using electroactive MOF thin films as the catalytic component in the electrocatalytic cell, either through (a) the use of the MOF structural elements themselves (ligands or nodes) as electroactive catalysts, or (b) the immobilization of high concentration of active molecular catalysts within the MOF pores (for a wide variety of energy-related catalytic reactions as hydrogen evolution, water oxidation, oxygen reduction, and CO2 reduction). Yet, up to this point, the notion of using MOFs to precisely tune and manipulate the properties of the electrocatalytically active site and its surrounding chemical environment was overlooked.

In this talk, we will demonstrate for the first time that a non-electrocatalytic MOF can be used as a porous membrane layered over a solid heterogeneous electrocatalyst.[1] Following this principle, a suitably designed MOF membrane has the potential to modify the microenvironment of the underlying heterogeneous catalyst and affect its electrocatalytic properties in a wide variety of proton-coupled electron transfer (PCET) reactions.

Solar energy conversion and storage in fuels and chemicals hold the potential to transform our largest CO₂-emitters such as the transport and electricity sectors and the chemical industry. Key approaches currently intensively studied for the generation of solar fuels are the direct conversion via photocatalysis and an indirect approach via electrocatalysis. For the water splitting reaction it has been modelled that both pathways could in principle achieve solar-to-hydrogen efficiencies of ~30%. In practice however, photocatalytic or photoelectrochemical systems have shown efficiencies of ≤10% and more commonly around 1%. This discrepancy invites to have a closer look at the material engineering in both approaches. Hence, in my talk I will highlight our recent studies on polycrystalline thin film Cu(In,Ga)Se₂ [1] commonly used in high-efficiency solar cells as well as on a promising oxide photocatalyst La,Rh:SrTiO₃ used in photocatalyst sheets to produce hydrogen [2]. Both studies give interesting insights into material design strategies for novel photocatalysts.

High entropy alloys (HEA) consist of 5 or more different elements, whose atomic positions in the crystal are determined by the entropy effect and therefore mixed randomly. As consequence, the active surface consists of millions of different possible atomic arrangements.

In catalysis, the scientific challenge is to control the active surface at the atomic scale. The conventional strategy is to microscopically control the specific structure of a uniform surface.  HEAs offer a completely new approach to discovering catalytic materials. The key strategy is to span a range of catalytic activities on a single HEA surface. The random atomic arrangement in a HEA ensures that some surface sites will have exactly the optimal bi-functional properties, which can overcome the limitations of the uniform structures found in today’s catalysts. The stoichiometry of the HEA changes the likelihood of these different sites to occur, thus by controlling the ratio of the different elements in the HEA it is possible to tune the number of the most active sites and thereby also tune the catalytic activity. The activity is therefore controlled by probability rather than microscopically.

Tailoring the structure of the electrochemical interface at the atomic and molecular levels is key for the rational design of new electrocatalysts for renewable energy conversion. Model studies on well-defined interfaces are pivotal to understanding the factors controlling both activity and selectivity in electrocatalysis. This talk will focus on new catalyst materials and engineered interfaces for electrochemical energy conversion. I will discuss structure sensitivity and electrolyte effects for different processes including oxygen and carbon dioxide electrocatalysis.

First, I will present our recent work on self-supported high surface area nanostructured Ir-based networks for the oxygen evolution reaction (OER). These networks show a unique morphology and combine excellent mass activity with promising stability. I will then discuss the role of anions from the electrolyte on Ir nanoparticles for OER. The last part of the talk will highlight the importance of carrying out model studies on Cu-based surfaces to understand structure-properties relations for CO₂ and CO reduction. We have investigated the interfacial properties of Cu single-crystalline electrodes in contact with different electrolytes. We have studied the effect of pH, specific anion adsorption, and potential dependence for CO reduction. We show how well-defined studies are essential to understand the structure-function relations and design efficient electrocatalysts for the production of renewable fuels and chemicals.

The electrochemical reduction of CO2 is a challenging reaction of interest from a fundamental
perspective and as a candidate for converting an environmentally harmful gas into a valuable fuel.
Application in large scale of this reaction will likely require the use of catalysts based on cheap and
abundant metals. Organometallic ruthenium complexes bearing a 2,2':6',2''-terpyridine paired with a
bidentate ligand containing mixed pyridine-N-heterocyclic carbene are well established
electrocatalysts for CO2 reduction to CO (Figure 1).[1] We recently unraveled the mechanism for this
system, and we proved that the two geometrical isomers resulting from the asymmetry of the bis-
chelating ligand have completely different behavior in the elementary steps of the catalytic cycle, as a
consequence the trans effect provided by the strongly donating NHC donor.[2,3] Now in this
contribution, we will discuss the synthesis of the iron analogues, as well as the mechanism of this new
family of electrocatalysts in CO2 reduction.[4] A combination of NMR spectroscopy, cyclic
voltammetry, and spectroelectrochemical infrared spectroscopy have established similarities and
differences between the catalytic cycle performed by iron and ruthenium complexes.

References:
[1] Z. Chen, C. Chen, D. R. Weinberg, P. Kang, J. J. Concepcion, D. P. Harrison, M. S. Brookhart, T. J.
Meyer, Chem. Commun. 2011, 47, 12607–12609. [2] S. Gonell, M. D. Massey, I. P. Moseley, C. K. Schauer, J. T. Muckerman, A. J. M. Miller, J. Am. Chem.
Soc. 2019, 141, 6658–6671. [3] S. Gonell, E. A. Assaf, K. D. Duffee, C. K. Schauer, A. J. M. Miller, J. Am. Chem. Soc. 2020, 142,
8980–8999. [4] S. Gonell, J. Lloret-Fillol, A. J. M. Miller, ACS Catal. 2021, 11, 615–626.

Ni single atoms supported on carbonaceous materials are an appealing solution to revalorize CO 2 due to the low cost and versatility of the support and the optimal usage of Ni and its predicted selectivity and efficiency. Herein, we have used noble carbonaceous support derived from cytosine to load Ni subnanometric sites. The large heteroatom content of the support allows the stabilization of up to 11 wt% of Ni without the formation of nanoparticles. EXAFS analysis points at Ni single atoms or subnanometric clusters coordinated by oxygen in the support. Unlike the well-known N-coordinated Ni single sites selectivity towards CO 2 reduction, O-coordinated-Ni single sites (ca. 7wt% of Ni) reduced CO 2 to CO, but subnanometric clusters (11 wt% of Ni) foster the unprecedented formation of HCOOH with 27% FE at -1.4V. Larger Ni amounts ended up on the formation of NiO nanoparticles and almost 100% selectivity towards HER.

Nowadays, the mitigation and reverse of the climate change is one of the main global challenges we, as a society, are facing. For this purpose, we must use and store renewable energy to be used as fuels, electricity or to produce fine chemicals. One of the most attractive alternatives is the use of sunlight to drive these processes given that the energy coming from the sun to Earth in one hour, if fully harnessed, is enough to energetically sustain the whole planet for a full year. In this context, using sunlight to drive redox transformations is a promising technology to decarbonize transportation, heating and fine chemicals sectors.

Sunlight driven processes are complex since they involve several steps that need to take place simultaneously in a harmoniously and synchronized manner. Firstly, the light, with the right energy, is absorbed by promoting electrons from the highest occupied energetic level (valence band in semiconductors) to the lowest unoccupied one (conduction band in semiconductors), generating oxidative equivalents (holes). These charges are accumulated to the surface/electrolyte interface, and holes are used to oxidise a substrate and the electrons will either be used to reduce protons, CO₂ to generate carbon-based products or N₂ to generate NH₃. When the oxidative reaction is water oxidation, this is the bottleneck of the whole solar- driven process.[1] Some approaches consider the possibility of substituting this demanding process for an organic molecule oxidation, which can be energetically less demanding and potentially also producing added value compounds.[2–4]

In this talk I will focus on the use of methanol and glycerol as substrates in the oxidative reaction using conventional metal oxide photoanodes: α-Fe₂O₃ and BiVO₄. [4] In addition, I will discuss the use of the combined electrochemical and optical technique to probe the catalytic function of these photoanodes under operational conditions. [5-7] This technique opens a new possibility of studying multielectron reaction mechanisms on non-ideal metal oxides. From these experiments I will discuss some kinetic mechanistic parameters important to design more efficient systems.

Along with mechanical, electrical, and thermal energy storage systems, chemical approaches have recently captured more attention of many sectors, giving some unique advantages. Among the most important, the flexibility of storing large quantities of energy over long periods at any location and lower costs per unity of stored energy is worth mentioning. Many chemical compounds, synthesized with renewable energy, are capable candidates to serve as chemical storage systems such as alcohols, hydrocarbons, and ammonia. In the case of ammonia, its versatile applications, either for power or as a chemical precursor, have put it at the center of an intensive attempt to develop technologies to replace its traditional forms of production (The Haber-Bosh process).

Upgrading nitrogen oxyanions to high-value nitrogen-based products is one promising approach for fuel, energy chemical storage, and chemical commodities production. Among several monometallic and bimetallic catalysts, copper and titanium have attracted attention because of their high ability to convert nitrate or nitrite into ammonia with an appreciable efficiency. Although numerous efforts have been made to achieve a combination of high nitrate conversion with a high partial current efficiency and selectivity to ammonia, it remains a challenge to obtain a high-quality bimetallic catalyst for the electroreduction of NO₃^- / NO₂^- that can reach all the mentioned efficiency parameters simultaneously. In this work, we analyze the performance in direct electroreduction of a high nitrate concentrated electrolyte of two different cathode materials (Cu Foil, Ti Foil) and the effects on the efficiency parameters of combining these materials in a bimetallic catalyst (Cu Nanoparticles / Ti Foil). In a 0.4 M KNO₃ electrolyte, the bimetallic electrocatalyst (CuNP deposited on Ti Foil) exhibits a better global efficiency in ammonia yield than the monometallic electrodes. The CuNP/Ti Foil electrocatalyst showed a Faradaic efficiency (FE) of 80% with a Selectivity (SE) of 54% and a total nitrate conversion of 17% at -750 mV vs. Reversible Hydrogen Electrode (RHE). Separately the monometallic electrodes showed high FE and SE to ammonia in the case of the Ti Foil (92%, 57%, respectively) and a high nitrate conversion capacity in the case of the Cu Foil (27%) at more negative potentials. The combination of all efficiency parameters suggests the synergistic effect of combining Cu and Ti in a promising bimetallic electrode for nitrate electroreduction to ammonia.

Perovskite nanocrystals (PNCs) have been highlighted as promissory materials in optoelectronics, due to improved light harvesting, photocarrier generation and the ease for tuning their optical properties, by varying their particle size and halide composition.[1] These features have opened the door to analogous solar driven process such as photo(electro)catalysis for carrying out the photodegradation of recalcitrant organic compounds more efficiently.[2] Nonetheless, there is a scarce in the state of the art about the photo(electro)chemical (PEC) properties of these materials in form of electrodes for establishing their oxidizing power in the oxidation of organics, and also it should be considered that the photocatalytic (PC) activity of PNCs mainly depends on the surface chemical environment formed during their synthesis. In this work, we show the ability of PNCs to perform photo(electro)catalytic degradation of targeted organic molecules as a proof-of-concept, and we also deduce how the nature of role of chemical states found in the PNCs surface and the purification of PbX₂ precursors dictates their photocatalytic activity. Then, we demonstrate that the PEC behavior of PNCs based photomaterials can be modulated by using diverse carrier transporting layers, fabricating selective photoelectrodes to carry out oxidation/reduction reactions. Lastly, modified PNCs with promising band structure and photoluminescence quantum yield up to 100% and lead-free ones are also addressed to have high potentiality for solar-driven chemical reactions.

There is a burgeoning interest in the development of a green method of ammonia synthesis; ammonia, already critical for fertilizers 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 highly 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 far too inefficient for practical uses; moreover, it is highly unstable.[1,2.3]

In the current contribution, we will explore the underlying reasons why lithium is unique in its ability to reduce nitrogen to ammonia. We use a combination of electrochemical experiments, Raman spectroscopy, time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and density functional theory.[4] By drawing from the adjacent fields of enzymatic nitrogen reduction and battery science, we will aim to build a holistic picture of the factors controlling nitrogen reduction.