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The lithium-mediated system catalyzes nitrogen to ammonia under ambient conditions. Herein we discover that trace amount of water as an electrolyte additive─in contrast to prior reports from the literature–can effect a dramatic improvement in the Faradaic selectivity of N2 reduction to NH3. We report that an optimal water concentration of 35.9 mM and LiClO4 salt concentration of 0.8 M allows a Faradaic efficiency up to 27.9 ± 2.5% at ambient pressure. We attribute the increase in Faradaic efficiency to the incorporation of Li2O in the solid electrolyte interphase, as suggested by our X-ray photoelectron spectroscopy measurements. Our results highlight the extreme sensitivity of lithium-mediated N2 reduction to small changes in the experimental conditions.

International audience; Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O$_2$) reduction at the cathode of proton exchange membrane fuel cells (PEMFCs) are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O$_2$ reduction, their controlled synthesis and stability for practical applications remains challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilisation remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, we addressed this issue by coordinating Fe in a highly porous nitrogen doped carbon support (~3295 m$^2$ g$^{-1}$), prepared by pyrolysis of inexpensive 2,4,6triaminopyrimidine and a Mg$^{2+}$ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54×10$^{19}$ sites g$_{FeNC}$$^{-1}$ and a record 52% FeN$_x$ electrochemical utilisation based on in situ nitrite stripping was achieved. The Fe single atoms are characterised pre-and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which were further studied by density functional theory calculations.

Electrolyte effects play an important role on the activity of the oxygen reduction reaction (ORR) of Pt-based electrodes. Herein, we combine a computational model and rotating disk electrode measurements to investigate the effects from phosphate anion poisoning for the ORR on well-defined extended Pt surfaces. We construct a model including the poisoning effect from phosphate species on Pt(111) and Cu/Pt(111) based on density functional theory simulations. We have investigated the effect of adsorbed phosphate species at low overpotentials when tuning *OH binding energies. Our work shows that, regardless of the surface site blockage from phosphate, the trend in catalytic oxygen reduction activity is predominately governed by the *OH binding.

The electrochemical CO2 reduction reaction (CO2RR) to value-added chemicals with renewable electricity is a promising method to decarbonise parts of the chemical industry. Recently, single metal atoms in nitrogen-doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, we synthesized two catalysts through a decoupled two-step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso-porous structure resulted in the highest reported electrochemical active site utilisation based on in situ nitrite stripping; up to 59±6% for NiNC. Ex-situ X-ray absorption spectroscopy confirmed the penta-coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. Our density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, we find that the TOFs of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates.

The Mo/Fe nitrogenase enzyme is unique in its ability to efficiently reduce dinitrogen to ammonia at atmospheric pressures and room temperature. Should an artificial electrolytic device achieve the same feat, it would revolutionise fertilizers and even provide an energy dense, truly carbon-free fuel. This Review provides a coherent comparison of recent progress made in dinitrogen fixation on (i) solid electrodes, (ii) homogeneous catalysts and (iii) nitrogenases. Specific emphasis is placed on systems for which there is unequivocal evidence that dinitrogen reduction has taken place. By establishing the cross-cutting themes and synergies between these systems, we identify viable avenues for future research.

The lithium-mediated system catalyses nitrogen to ammonia under ambient conditions. Herein we discover that trace amount of water - in contrast to prior reports from the literature – can effect a dramatic improvement in the Faradaic selectivity of N2 reduction to NH3. We report an optimal water concentration of 35.5 mM and LiClO4 salt concentration of 0.8 M allows a Faradaic efficiency up to 27.7% at ambient pressure. We attribute the increase in Faradaic efficiency to the incorporation of Li2O in the solid electrolyte interphase, as suggested by our X-ray photoelectron spectroscopy measurements. Our results highlight the extreme sensitivity of lithium mediated N2 reduction to small changes in the experimental conditions.

Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O2) reduction at the cathode of proton exchange membrane fuel cells (PEMFCs) are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O2 reduction, their controlled synthesis and stability for practical applications remains challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilisation remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, we addressed this issue by coordinating Fe in a highly porous nitrogen doped carbon support (~3295 m2 g-1), prepared by pyrolysis of inexpensive 2,4,6-triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54×10^19 sites gFeNC-1 and a record 52% FeNx electrochemical utilisation based on in situ nitrite stripping was achieved. The Fe single atoms are characterised pre- and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which were further studied by density functional theory calculations.

Cu is currently the most effective monometallic catalyst for producing valuable multicarbon-based (C2+) products, such as ethylene and ethanol, from the CO2reduction reaction (CO2RR). One approach to optimize the activity and selectivity of the metal Cu catalyst is to functionalize the Cu electrode with a molecular modifier. We investigate from a data standpoint whether any reported functionalized Cu catalyst improves the intrinsic activity and/or multicarbon product selectivity compared to the performance of bare Cu foil and the best single crystal Cu facets. Our analysis shows that the reported increases in activity are due to increased surface roughness and disappear once normalized with respect to electrochemical surface area. The intrinsic activity generally falls below that of the bare Cu foil reference, both for total and product-specific current, which we attribute to nonselective blocking of active sites by the modifier on the surface. Instead, an analysis of various polymer diffusion coefficients indicates that the modifier allows for easier diffusion of CO2compared to H2O to the surface, leading to greater selectivity for CO2RR and C2+products. As such, our analysis finds no catalyst for CO2RR that intrinsically outperforms bare Cu.

Electrocatalytic conversion is a promising technology for storing renewable electricity in the chemical form. Substantial efforts have been made on the multi-carbon feedstock production,while producing nitrogen-containing chemicals like urea via C-N coupling little is known. Here, we elucidate the possible urea production on metals through co-reduction of nitric oxide (NO) and carbon oxide (CO). Based on adsorption energies calculated by DFT, we find that Cu is able to bind both *NO and *CO while not binding *H. During NO + CO co-reduction, we identify two kinetically and thermodynamically possible C-N couplings via *CO + *N and *CONH + *N, and further hydrogenation leads to urea formation. A 2-D activity heatmap has been constructed for describing nitrogen conversion to urea. This work provides a clear example of using computational simulations to predict selective and active materials for sustainable urea production.

Electrocatalytic conversion is a promising technology for storing renewable electricity in the chemical form. Substantial efforts have been made on the multi-carbon feedstock production,while producing nitrogen-containing chemicals like urea via C-N coupling little is known. Here, we elucidate the possible urea production on metals through co-reduction of nitric oxide (NO) and carbon oxide (CO). Based on adsorption energies calculated by DFT, we find that Cu is able to bind both *NO and *CO while not binding *H. During NO + CO co-reduction, We identify two kinetically and thermodynamically possible C-N couplings via CO + *N and CONH + *N, and further hydrogenation leads to urea formation. A 2-D activity heatmap has been constructed for describing nitrogen conversion to urea. This work provides a clear example of using computational simulations to predict selective and active materials for sustainable urea production.

Cu is currently the most effective monometallic catalyst for producing valuable multi-carbon-based products, such as ethylene and ethanol, from the CO2 reduction reaction (CO2RR). One approach to optimize the activity and selectivity of the metal Cu catalyst is to functionalize the Cu electrode with a molecular modifier. We investigate from a data standpoint whether any reported functionalized Cu catalyst improves the intrinsic activity and/or multi-carbon product selectivity compared to the performance of bare Cu foil and the best single crystal Cu facets. Our analysis shows that the reported increases in activity are due to increased surface roughness and disappear once normalizing with respect to electrochemical surface area. The intrinsic activity generally falls below that of bare Cu foil, both for total and product-specific current, which we attribute to non-selective blocking of active sites by the modifier on the surface. Instead, we show that the modifier allows for easier diffusion of CO2 compared to H2O to the surface, leading to greater selectivity for CO2RR and C2+ products. As such, our analysis finds no catalyst for CO2RR that intrinsically outperforms bare Cu.

(Bi)carbonate adsorption on Cu(100) in 0.1 M KHCO3 has been studied by in situ scanning tunneling microscopy. Coexistence of different ordered adlayer phases with ( 2 ${\sqrt{2}}$ x6 2 ${\sqrt{2}}$ )R45 degrees and (4x4) unit cells was observed in the double layer potential regime. The adlayer is rather dynamic and undergoes a reversible order-disorder phase transition at 0 V vs. the reversible hydrogen electrode. Density functional calculations indicate that the adlayer consists of coadsorbed carbonate and water molecules and is strongly stabilized by liquid water in the adjacent electrolyte.

High-entropy alloy (HEA) electrocatalysts offer a vast composition space that awaits exploration to identify interesting materials for energy conversion reactions. While attempts have been made to explore the composition space of HEA thin-film libraries and compare experimental and computational studies, no corresponding approaches exist for HEA nanoparticles. So far, catalytic investigations on HEA nanoparticles are limited to small sets of individual catalysts. Here, we report the experimental exploration of the composition space of carbon-supported Pt−Ru−Pd−Rh− Au nanoparticles for the H2/CO oxidation reaction by constructing a dataset using Bayesian optimization as guidance. Applying a surfactant-free synthesis platform, a dataset of 68 samples was investigated. By constructing machine learning models, the relationship between the concentrations of the constituent elements and the catalytic activity was analyzed and compared to density functional theory calculations. The machine learning models confirm findings from previous studies concerning the role of Ru in the H2/CO oxidation reaction. This has been achieved starting from a random set of compositions and without any prior assumptions for the reaction mechanism nor any in-depth design of the active site. In addition, by comparing the trends of the computational and experimental studies, it is seen that the “onset potentials” across the compositions can be correlated with the adsorption energy of *OH. The best correlation between the computational and experimental data is obtained when considering 5% of the most strongly *OH adsorbing sites.

Electrocatalytic conversion of formic acid oxidation to CO2 and the related CO2 reduction to formic acid represent a potential closed carbon-loop based on renewable energy. However, formic acid fuel cells are inhibited by the formation of site-blocking species during the formic acid oxidation reaction. Recent studies have elucidated how the binding of carbon and hydrogen on catalyst surfaces promote CO2 reduction towards CO and formic acid. This has also given fundamental insights to the reverse reaction, i.e. the oxidation of formic acid. In this work, simulations on multiple materials have been combined with formic acid oxidation experiments on electrocatalysts to shed light on the reaction and the accompanying catalytic limitations. We correlate data on different catalysts to show that (i) formate, which is the proposed formic acid oxidation intermediate, has similar binding energetics on Pt, Pd and Ag, while Ag does not work as catalyst, and (ii) *H adsorbed on the surface results in *CO formation and poisoning through a chemical disproportionation step. Using these results, the fundamental limitations can be revealed and progress our understanding of the mechanism of the formic acid oxidation reaction .

Since its verification in just 2019, there have been numerous high-profile papers reporting improved efficiency of the lithium-mediated electrochemical nitrogen reduction system to make ammonia. However, the literature lacks a cohesive investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we vary electrolyte salt concentration and observe a transition from an unstable working electrode potential to working electrode potential stability and peak in Faradaic efficiency of 7.8 ± 0.5 % at 0.6 M LiClO4. The behaviour is linked to the formation of Solvent Separated Ion Pairs in the electrolyte through Raman spectroscopy. Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy reveal a more inorganic, and therefore more stable, SEI layer with increasing salt concentration. A drop in Faradaic efficiency is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a loss in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by Electrochemical Impedance Spectroscopy.

Cu is currently the most effective monometallic catalyst for producing valuable multi-carbon-based products, such as ethylene and ethanol, from the CO2 reduction reaction (CO2RR). One approach to optimize the activity and selectivity of the metal Cu catalyst is to functionalize the Cu electrode with a molecular modifier. We investigate from a data standpoint whether any reported functionalized Cu catalyst improves the intrinsic activity and/or multi-carbon product selectivity compared to the performance of bare Cu foil and the best single crystal Cu facets. Our analysis shows that the reported increases in activity are due to increased surface roughness and disappear once normalizing with respect to electrochemical surface area. The intrinsic activity generally falls below that of bare Cu foil, both for total and product-specific current, which we attribute to non-selective blocking of active sites by the modifier on the surface. Instead, we show that the modifier allows for easier diffusion of CO2 compared to H2O to the surface, leading to greater selectivity for CO2RR and C2+ products. As such, our analysis finds no catalyst for CO2RR that intrinsically outperforms bare Cu.

Cu electrodes are promising materials to catalyze the conversion of CO2 and CO into renewable fuels and valuable chemicals. However, a detailed description of the properties of the Cu–electrolyte i...

A challenge in the electrochemical CO2 reduction reaction (CO2RR) is the lack of efficient and selective electrocatalysts to valuable chemicals. Hydrocarbons and valuable chemicals from the CO2RR h...

Cyclic voltammograms are key to much of the accumulated understanding of the nature of electrochemical interfaces; however, they provide no direct information on the atomic structure of the interfa...

The electrocatalytic nitrogen reduction reaction (NRR) under mild conditions is one of the most essential challenges in chemistry. Catalysts for electrochemical NRR play a crucial role in realizing this NH3 synthesis. In this work, we use density functional theory simulations to investigate the electrocatalytic NRR selectivity and activity on dual-atom catalysts, especially diporphyrins. We classify catalysts on the basis of the adsorption of ∗N2 versus ∗H. Our results demonstrate the possibility of diporphyrins to bind and reduce N2 without producing H2 at ambient conditions, promoting the high selectivity towards NH3 formation. This is due to a chelating adsorption of N2, where N2 sits between two metal atoms, enhancing the binding of ∗N2. Additionally, the chelating adsorption of N2 activates N-N bond breaking and provides more favourable scaling relations on the adsorption energies of key intermediates, leading to the enhanced NRR activity.

The catalytic reduction of CO2/CO is key to reducing the carbon footprint and producing the chemical building blocks needed for society. In this work, we performed a theoretical investigation of the differences and similarities of the CO2/CO catalytic reduction reactions in gas, aqueous solution, and aprotic solution. We demonstrate that the binding energy serves as a good descriptor for the gaseous and aqueous phases and allows catalysts to be categorized by reduction products. The CO* vs O* and CO* vs H* binding energies for these phases give a convenient mapping of catalysts regarding their main product for the CO2/CO reduction reactions. However, for the aprotic phase, descriptors alone are insufficient for the mapping. We show that a microkinetic model (including the CO* and H* binding energies) allows spanning and interpreting the reaction space for the aprotic phase.

Electrocatalytic conversion of formic acid oxidation to CO2 and the related CO2 reduction to formic acid represent a potential closed carbon-loop based on renewable energy. However, formic acid fuel cells are inhibited by the formation of poisoning species during the reaction. Recent studies have elucidated how the binding of carbon and hydrogen on catalyst surfaces promote CO2 reduction towards CO and formic acid. This has also given fundamental insights to the reverse reaction, i.e. the oxidation of formic acid. In this work, simulations on multiple materials have been combined with formic acid oxidation experiments on electrocatalysts to shed light on the reaction and the accompanying catalytic limitations. We found that: (i) The desired principal reaction for efficient formic acid oxidation should progress through adsorbed carboxyl, *COOH, which should then be oxidized to CO2. (ii) *H adsorbed on the surface results in *CO formation and poisoning through a chemical disproportionation step. (iii) Catalysts are poisoned by formate and/or hydroxyl. Using these results, a framework for the reaction has been developed explaining the fundamental limitations and progressing our understanding.

The catalytic reduction of CO2/CO is key to reducing carbon footprint and producing the chemical building blocks needed for society. In this work, we performed a theoretical investigation of the differences and similarities of the CO2/CO catalytic reduction reactions in the gas, aqueous solution, and aprotic solution. We demonstrate that binding energy serves as a good descriptor for gaseous and aqueous phases and allows categorizing catalysts by reduction products. The CO vs. O and CO vs. H binding energies for these phases gives a convenient mapping of catalysts regarding their main product for the CO2/CO reduction reactions. However, for the aprotic phase, descriptors alone are insufficient for the mapping. We show that a microkinetic model (including the CO and H binding energies) allows spanning and interpreting the reaction space for the aprotic phase.

In recent years, the development of complex multi-metallic nanomaterials like high entropy alloy (HEA) catalysts has gained popularity. Composed of 5 or more metals, the compositions of HEAs exhibit extreme diversity. This is both a promising avenue to identify new catalysts and a severe constraint on their preparation and study. To address the challenges related to the preparation, study and optimization of HEAs, machine learning solutions are attractive. In this paper, the composition of PtRuPdRhAu hydrogen oxidation catalysts is optimized for the CO oxidation reaction. This is achieved by constructing a dataset using Bayesian optimization as guidance. For this quinary nanomaterial, the best performing composition was found within the first 35 experiments. However, the dataset was expanded until a total of 68 samples were investigated. This final dataset was used to construct a random forest regression model and a linear model. These machine learned models were used to assess the relationships between the concentrations of the consituent elements and the CO oxidation reaction onset potential. The onset potentials were found to correlate with the composition dependent adsorption energy of *OH obtained from density functional theory. This study demonstrates, how machine learning can be employed in an experimental setting to investigate the vast compositional space of HEAs.

In recent years, the development of complex multi-metallic nanomaterials like high entropy alloy (HEA) catalysts has gained popularity. Composed of 5 or more metals, the compositions of HEAs exhibit extreme diversity. This is both a promising avenue to identify new catalysts and a severe constraint on their preparation and study. To address the challenges related to the preparation, study and optimization of HEAs, machine learning solutions are attractive. In this paper, the composition of PtRuPdRhAu hydrogen oxidation catalysts is optimized for the CO oxidation reaction. This is achieved by constructing a dataset using Bayesian optimization as guidance. For this quinary nanomaterial, the best performing composition was found within the first 35 experiments. However, the dataset was expanded until a total of 68 samples were investigated. This final dataset was used to construct a random forest regression model and a linear model. These machine learned models were used to assess the relationships between the concentrations of the consituent elements and the CO oxidation reaction onset potential. The onset potentials were found to correlate with the composition dependent adsorption energy of *OH obtained from density functional theory. This study demonstrates, how machine learning can be employed in an experimental setting to investigate the vast compositional space of HEAs.

We present an approach for a probabilistic and unbiased discovery of selective and active catalysts for the carbon dioxide (CO2) and carbon monoxide (CO) reduction reactions on high-entropy alloys ...

Corrosion of copper is an expensive degradation process of materials in engineered infrastructures and in various technical applications. It is also an important factor in the geological disposal o...

Unlike energy efficiency and selectivity challenges, the kinetic effects of impure or intentionally mixed CO2 feeds on the catalytic reactivity of the direct electrochemical CO2 reduction reaction (CO2RR) have been poorly studied. Given that industrial CO2 feeds are often contaminated with CO, a closer investigation of the CO2RR under CO2/CO co-feed conditions is warranted. Here, we report mechanistic insights into the CO2RR reactivity of CO2/CO co-feeds on Cu-based nanocatalysts. Kinetic isotope-labelling experiments—performed in an operando differential electrochemical mass spectrometry capillary flow cell with millisecond time resolution—showed an unexpected enhanced production of C2H4, with a yield increase of almost 50%, from a cross-coupled 12CO2–13CO reactive pathway. The results suggest the absence of site competition between CO2 and CO molecules on the reactive surface at the reactant-specific sites. The practical significance of sustained local interfacial CO partial pressures under CO2 depletion is demonstrated by metallic/non-metallic Cu/Ni–N-doped carbon tandem catalysts. Our findings show the mechanistic origin of improved C2 product formation under co-feeding, but also highlight technological opportunities of impure CO2/CO process feeds for H2O/CO2 co-electrolysers. The mechanistic electrochemical mass spectrometry study of ethylene production on Cu-based nanocatalysts under CO2/CO co-feeds indicates the existence of separate, non-scrambling reactant-specific surface adsorption sites for CO2 and CO, which provides guidance for the design of CO2 reduction reaction electrocatalysts.

For CO2 reduction reactions, the Cu catalyst is unique, as compared with other metals, because of its ability to produce a wide range of hydrocarbon and oxygenated products. Previously, we have sho...

The electrochemical CO2 reduction reaction (CO2RR) is a promising technology for converting waste CO2 into chemicals which could be used as feedstock for the chemical industry or as synthetic fuels...

We report a joint experimental–computational mechanistic study of electrochemical reduction of CO2 to CH4, catalyzed by solid-state Fe–N–C catalysts, which feature atomically dispersed, catalytical...

The lithium-mediated method of electrochemical nitrogen reduction, pioneered by Tsuneto et al1 then verified by Andersen et al2, is currently the sole paradigm capable of unequivocal electrochemical ammonia synthesis. Such a system could allow the production of green, distributed ammonia for use as fertiliser or a carbon-free fuel. However, despite great improvements in Faradaic efficiency and stability since just 20193, fundamental understanding of the mechanisms governing nitrogen reduction and other parasitic reactions is lacking. Lithium Ion Battery (LIB) research can provide insight; since both lithium-mediated electrochemical ammonia synthesis and LIBs utilise an organic solvent and lithium salt, both form a Solid Electrolyte Interphase (SEI), which is electronically insulating but ionically conducting, at the electrode surface. In LIBs, this is necessary to stabilize and cycle low potential materials4. In lithium-mediated ammonia synthesis, the SEI could also have a critical role in controlling the access of protons and other key reactants to the catalytically active sites and promoting greater selectivity toward nitrogen reduction to ammonia5. While some characterisation of the SEI has been carried out for the lithium-mediated nitrogen reduction system6, the literature still lacks holistic studies which aim to carefully characterise the bulk electrolyte and SEI components and link them to system performance. In this work we use insight from battery science to tackle a significant stability problem in lithium-mediated nitrogen reduction. The traditional electrolyte employed by Tsuneto et al. was 0.2 M LiClO4 in a 99:1 tetrahydrofuran to ethanol mix. While this system can produce ammonia, the working electrode potential becomes more negative over time. Our initial investigations show that this problem stems from an unstable SEI which becomes increasingly organic. Simply by raising the concentration of LiClO4 in the electrolyte, we vastly improve stability, as shown in figure 1(a), and boost Faradaic efficiency. Bulk electrolyte salt solvation properties are investigated through Raman spectroscopy, as shown in figure 1(b). Here we observe the emergence of a shoulder at around 930 cm-1 with increasing LiClO4 concentration, which we assign to the emergence of Contact-Ion-Pairs (CIPs) through comparison to Density Functional Theory calculations. These CIPs mean that perchlorate anion degradation products are more abundant in the formed SEI, as shown in our X-Ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass spectrometry results. This more inorganic SEI protects the electrolyte against further degradation, preventing the working electrode drift to more negative potentials. We then link this behaviour to a peak observed in the Faradaic efficiency of ammonia synthesis at 0.6 M LiClO4 by also considering decreasing N2 solubility and diffusivity, as well as a more ionically conductive SEI, in an increasingly concentrated electrolyte. We also present never-before seen cross-sectional images of the SEI using cryogenic Focussed Ion Beam milling and Scanning Electron Microscopy, further aiding understanding of how salt solvation affects the morphology of the formed SEI and system performance. Our results emphasise the need to consider SEI properties in electrolyte design for lithium-mediated nitrogen reduction, as well as the need to balance desirable SEI properties with desirable bulk electrolyte properties. Tsuneto, A., Kudo, A. & Sakata, T. Efficient Electrochemical Reduction of N 2 to NH 3 Catalyzed by Lithium . Chemistry Letters vol. 22 851–854 (1993). Andersen, S. Z. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019). Westhead, O., Jervis, R. & Stephens, I. E. L. Is lithium the key for nitrogen electroreduction? Science. 372, 1149–1150 (2021). Peled, E. & Menkin, S. Review—SEI: Past, Present and Future. J. Electrochem. Soc. 164, A1703–A1719 (2017). Singh, A. R. et al. Electrochemical Ammonia Synthesis—The Selectivity Challenge. ACS Catal. 7, 706–709 (2017). Li, K. et al. Enhancement of lithium-mediated ammonia synthesis by addition of oxygen. Science. 1597, 1593–1597 (2021). Figure 1

Electrocatalytic denitrifification is a promising technology for removing NOx species (NO3−, NO2− and NO). For NOx electroreduction (NOxRR), there is a desire for understanding the catalytic parameters that control the product distribution. Here, we elucidate selectivity and activity of catalyst for NOxRR. At low potential we classify metals by the binding of ∗NO versus ∗H. Analogous to classifying CO2 reduction by ∗CO vs ∗H, Cu is able to bind ∗NO while not binding ∗H giving rise to a selective NH3 formation. Besides being selective, Cu is active for the reaction found by an activity-volcano. For metals that does not bind NO the reaction stops at NO, similar to CO2-to-CO. At potential above 0.3 V vs RHE, we speculate a low barrier for N coupling with NO causing N2O formation. The work provide a clear strategy for selectivity and aims to inspire future research on NOxRR.

The Haber-Bosch process conventionally reduces N-2 to ammonia at 200 bar and 500 degrees C. Under ambient conditions, i.e., room temperature and ambient pressure, N-2 can be converted into ammonia by the nitrogenase molecule and lithium-containing solid electrodes in nonaqueous media. In this work, we explore the catalyst space for the N-2 reduction reaction under ambient conditions. We describe N-2 reduction on the basis of the *N-2 binding energy versus the *H binding energy; we find that under standard conditions, no catalyst can bind and reduce *N-2 without producing H-2. We show why a selective catalyst for N-2 reduction will also likely be selective for CO2 reduction, but N-2 reduction is intrinsically more challenging than CO2 reduction. Only by modulating the reaction pathway, like nitrogenase, or by tuning chemical potentials, like the Haber-Bosch and the Li-mediated process, N-2 can be reduced.

Herein, we have investigated the interfacial properties of Cu(111) and Cu(100) in phosphate buffer solutions at different pH conditions and in presence of CO. Ab initio molecular simulations of the Cu-electrolyte interface were combined with voltammetric experiments carried out on Cu(100) and Cu(111) single-crystalline electrodes. We show that the adsorption strength of phosphate species on the different Cu facets affects the potential range at which CO poisons the surface. The properties of the Cu-electrolyte interface controls the potential range for CO reduction on Cu.

The electrochemical CO2 reduction reaction (CO2RR) to pure CO streams in electrolyzer devices is poised to be the most likely process for near-term commercialization and deployment in the polymer industry. The reduction of CO2 to CO is electrocatalyzed under alkaline conditions on precious group metal (PGM) catalysts, such as silver and gold, limiting widespread application due to high cost. Here, we report on an interesting alternative, a PGM-free nickel and nitrogen-doped porous carbon catalyst (Ni–N–C), the catalytic performance of which rivals or exceeds those of the state-of-the-art electrocatalysts under industrial electrolysis conditions. We started from small scale CO2-saturated liquid electrolyte H-cell screening tests and moved to larger-scale CO2 electrolyzer cells, where the catalysts were deployed as Gas Diffusion Electrodes (GDEs) to create a reactive three-phase interface. We compared the faradaic CO yields and CO partial current densities of Ni–N–C catalysts to those of a Ag-based benchmark, and its Fe-functionalized Fe–N–C analogue under ambient pressures, temperatures and neutral pH bicarbonate flows. Prolonged electrolyzer tests were conducted at industrial current densities of up to 700 mA cm−2. Ni–N–C electrodes are demonstrated to provide CO partial current densities above 200 mA cm−2 and stable faradaic CO efficiencies around 85% for up to 20 hours (at 200 mA cm−2), unlike their Ag benchmarks. Density functional theory-based calculations of catalytic reaction pathways help offer a molecular mechanistic basis of the observed selectivity trends on Ag and M–N–C catalysts. Computations lend much support to our experimental hypothesis as to the critical role of N-coordinated metal ion, Ni–Nx, motifs as the catalytic active sites for CO formation. Apart from being cost effective, the Ni–N–C powder catalysts allow flexible operation under acidic, neutral, and alkaline conditions. This study demonstrates the potential of Ni–N–C and possibly other members of the M–N–C materials family to replace PGM catalysts in CO2-to-CO electrolyzers.

The electrochemical CO2 reduction reaction (CO2RR) is a promising route for converting CO2 and excess renewable energy into valuable chemicals and synthetic fuels. Recently, carbon-based solid materials containing dopant-levels of transition metal and nitrogen (M–N–C) have emerged as a cost-effective, energy-efficient catalyst for the direct coreduction of CO2 and H2O to CO. Fe–N–C catalysts are particularly interesting as they can reduce CO further to hydrocarbons. Despite these promising reports, the influence of the reaction conditions on the catalytic performance of Fe–N–C catalysts has not been addressed. Here, we study the role of the electrolyte on the CO2RR selectivity. Unlike hydrogen or methane generation, catalytic CO production is independent of the electrolyte pH on the normal hydrogen electrode potential scale, suggesting a decoupled elementary proton–electron transfer mechanism for CO formation. The similarity between this heterogeneous charge-transfer reaction mechanism and that of molecul...

The electrochemical oxidation of methane to methanol at remote oil fields where methane is flared is the ultimate solution to harness this valuable energy resource. In this study we identify a fundamental surface catalytic limitation of this process in terms of a compromise between selectivity and activity, as oxygen evolution is a competing reaction. By investigating two classes of materials, rutile oxides and two-dimensional transition metal nitrides and carbides (MXenes), we find a linear relationship between the energy needed to activate methane, i.e. to break the first C-H bond, and oxygen binding energies on the surface. Based on a simple kinetic model we can conclude that in order to obtain sufficient activity oxygen has to bind weakly to the surface but there is an upper limit to retain selectivity. Few potentially interesting candidates are found but this relatively simple description enables future large scale screening studies for more optimal candidates.

In this work we propose four non-coupled binding energies of intermediates as descriptors, or 'genes', for predicting the product distribution in CO2 electroreduction. Simple reactions can be understood by the Sabatier principle (catalytic activity vs. one descriptor), while more complex reactions tend to give multiple very different products and consequently the product selectivity is a more complex property to understand. We approach this, as a logistical classification problem, by grouping metals according to their major experimental product from CO2 electroreduction: H2, CO, formic acid and beyond CO* (hydrocarbons or alcohols). We compare the groups in terms of multiple binding energies of intermediates calculated by density functional theory. Here we find three descriptors to explain the grouping: the adsorption energies of H*, COOH* and CO*. To further classify products beyond CO*, we carry out formaldehyde experiments on Cu, Ag and Au and combine these results with the literature to group and differentiate alcohol or hydrocarbon products. We find that the oxygen binding (adsorption energy of CH3O*) is an additional descriptor to explain the alcohol formation in reduction processes. Finally, the adsorption energy of the four intermediates, H*, COOH*, CO* and CH3O*, can be used to differentiate, group and explain products in electrochemical reduction processes involving CO2, CO and carbon-oxygen compounds.