Increasing the electrode thickness, thereby reducing the proportion of inactive cell components, is one way to achieve higher-energy-density lithium-ion batteries. This, however, results in higher electronic and ionic overpotentials and/or mechanical failure induced by binder migration. Here, we report ethanol-induced phase inversion as an effective method for making high-mass-loading nickel-rich, layered oxide (LiNi0.8Mn0.1Co0.1O2 [NMC811]) electrodes. The ethanol-induced phase inversion electrodes significantly outperform their conventionally processed counterparts with similar loading (35 mg/cm2) and porosity (30%) in Li/NMC half-cells (131.7 mAh/g vs. 56.7 mAh/g) at 1C (7 mA/cm2) discharge. The binder structure induced by the nonsolvent improves the pore connectivity and results in lower tortuosity factors. The rapid solvent removal reduces the binder migration during drying, enabling ultrahigh active mass loadings up to 60 mg/cm2 (12 mAh/cm2). Further, the compatibility of the phase inversion process with current roll-to-roll coating setups makes this a processing technique with high industrial feasibility.@en

The electrochemical CO₂ reduction reaction (CO₂RR) is an attractive method to produce renewable fuel and chemical feedstock using clean energy sources. Formate production represents one of the most economical target products from CO₂RR but is primarily produced using post-transition metal catalysts that require comparatively high overpotentials. Here a composition of bimetallic Cu–Pd is formulated on 2D Ti₃C₂T_x (MXene) nanosheets that are lyophilized into a highly porous 3D aerogel, resulting in formate production much more efficient than post-transition metals. Using a membrane electrode assembly (MEA), formate selectivities >90% are achieved with a current density of 150 mA cm⁻² resulting in the highest ever reported overall energy efficiency of 47% (cell potentials of −2.8 V), over 5 h of operation. A comparable Cu-Pd aerogel achieves near-unity CO production without the MXene templating. This simple strategy represents an important step toward the experimental demonstration of 3D-MXenes-based electrocatalysts for CO₂RR application and opens a new platform for the fabrication of macroscale aerogel MXene-based electrocatalysts.

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Electrochemical reduction of CO₂ presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.

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Ammonia is an indispensable commodity and a potential carbon free energy carrier. The use of H permeable electrodes to synthesize ammonia from N ₂, water and electricity, provides a promising alternative to the fossil fuel based Haber-Bosch process. Here, H permeable Ni electrodes are investigated in the operating temperature range 25–120 °C, and varying the rate of electrochemical atomic hydrogen permeation. At 120 °C, a steady reaction is achieved for over 12 h with 10 times higher cumulative NH ₃ production and almost 40-fold increase in faradaic efficiency compared to room temperature experiments. NH ₃ is formed with a cell potential of 1.4 V, corresponding to a minimum electrical energy investment of 6.6 kWh kg ⁻¹ (Figure presented.). The stable operation is attributed to a balanced control over the population of N, NH _x and H species at the catalyst surface. These findings extend the understanding on the mechanisms involved in the nitrogen reduction reaction and may facilitate the development of an efficient green ammonia synthesis process.

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The electrochemical dinitrogen reduction reaction (NRR) has recently gained much interest as it can potentially produce ammonia from renewable intermittent electricity and replace the Haber-Bosch process. Previous literature studies report Fe- and Mo-carbides as promising electrocatalysts for the NRR with activities higher than other metals. However, recent understanding of extraneous ammonia and nitrogen oxide contaminations have challenged previously published results. Here, we critically assess the NRR performance of several Fe- and Mo-carbides reported as promising by implementing a strict experimental protocol to minimize the effect of impurities. The successful synthesis of α-Mo₂C decorated carbon nanosheets, α-Mo₂C nanoparticles, θ-Fe₃C nanoparticles, and χ-Fe₅C₂ nanoparticles was confirmed by X-ray diffraction, scanning and transmission electron microscopy, and X-ray photoelectron and Mössbauer spectroscopy. After performing NRR chronoamperometric tests with the synthesized materials, the ammonia concentrations varied between 37 and 124 ppb and are in close proximity with the estimated ammonia background level. Notwithstanding the impracticality of these extremely low ammonia yields, the observed ammonia did not originate from the electrochemical nitrogen reduction but from unavoidable extraneous ammonia and NO_x impurities. These findings are in contradiction with earlier literature studies and show that these carbide materials are not active for the NRR under the employed conditions. This further emphasizes the importance of a strict protocol in order to distinguish between a promising NRR catalyst and a false positive.

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In the last century, the indiscriminate use of fossil energy to power the industrial revolution and technological progress of humankind, has led to the depletion of limited natural resources and, most importantly, the emission and accumulation of alarming levels of pollutants and greenhouse gases (GHG) in the atmosphere. One of the major consequences of these emissions is the climate crisis that we are currently facing. As our society is in constant need for energy to live and progress, we are urged to find more sustainable and renewable energy sources, and to decrease the environmental impact of industrial processes. Electrochemistry can be used to temporary store intermittent renewable electricity, to then be reconverted back to electrons, or it can be used to produce chemicals. As such, the electrification of the chemical industry offers the opportunity to reduce its GHG footprint. The variable supply of renewable electricity can be used by the chemical industry to generate artificial fuel and feedstock. In this way, the synergy between the chemical industry and the energy sector can boost market access, scale and competitiveness. In particular, this thesis focuses on one of the largest processes in chemical industry, i.e. the ammonia production. An introduction on the topic is given in Chapter 1. Ammonia is produced at large scale (178 million tons per year) and it is a commodity essential for the fertiliser and food sector. The current production of ammonia, via the Haber-Bosch process, relies on fossil fuels and hydrogen derived from steam-methane reforming. Consequently the sector is responsible for releasing 1.4 % of the global CO2 emissions. The implementation of a fully renewable powered Haber-Bosch process is limited by its large reactor scale and its continuous and steady operation, which clashes with the intrinsic intermittency of sources such as solar and wind. This is one of the reasons why a direct electrochemical route for ammonia synthesis has recently attracted significant attention in the scientific and industrial communities. The concept entails the direct synthesis of ammonia from water, dinitrogen and renewable electricity. Moreover, the possibility of producing ammonia in a sustainable manner may enable a new scenario where ammonia can also be used as carbon free energy carrier, thus playing a key role in a decarbonised energy landscape powered by renewables. However, the lack of a selective catalyst and the arduous competition with side reactions, as the hydrogen evolution reaction, make this process extremely challenging. The aim of this thesis is to expand the current understanding of the nitrogen reduction reaction at near ambient conditions, addressing both fundamental and practical challenges. The first part of this thesis (Chapter 2-4) provides insights on the implementation of reliable electrochemical nitrogen reduction experiments and sensitive operando ammonia detection. Chapter 2 provides a fast and reliable ammonia detection method to speed-up catalyst screening and development of novel sustainable ammonia evolution devices, as it requires significantly less sample handling and preparation compared to other reported methods. The proposed method is based on a gas chromatography technique, and it allows for in situ monitoring of ammonia evolution, down to 150 ppb, from -but not limited to- electrochemical devices. Chapter 3 presents an isotope sensitive gas chromatography-mass spectrometry method for the quantification of NH3 at low concentration level, typically encountered in electrochemical ammonia synthesis applications. This method allows the discrimination of 15/14NH3, necessary for the required 15N2 isotope labelling control experiments. Additionally, this method can directly and simultaneously measure other species in the analyte, thus it allows researchers to directly assess reaction selectivity by measuring reaction by-products, as well as the presence of gaseous/volatile contaminants in the experimental setup. Chapter 4 investigates the impact of contaminations on electrochemical nitrogen reduction experiments, with the aid of multiple analytical techniques and instrumentation, such as ion chromatography, gas chromatography, mass spectrometry, NOx chemiluminescence analyser and UV-Vis spectrophotometry. This chapter not only provides a comprehensive identification and quantification of the contaminations, but it also critically analyses the effectiveness of different cleaning strategies, establishing a series of guidelines to perform reliable experiments. The second part of this thesis (Chapter 5-7) investigates the room temperature spontaneous dinitrogen activation on selected metallic surfaces and its hydrogenation to ammonia via electrochemical atomic hydrogen permeation, using a solid metallic hydrogen permeable membrane electrode. Chapter 5 demonstrates a novel strategy for ambient condition ammonia synthesis from water and dinitrogen, designed to limit the competition between nitrogen activation and other competing adsorbates at the catalytic surface. As such, a hydrogen permeable nickel membrane electrode is used to spatially separate the electrolyte and the hydrogen activation side from the nitrogen activation and hydrogenation sites. With this approach, ammonia is produced catalytically directly in the gas phase and in the absence of electrolyte. Gaseous nitrogen activation at the nickel electrode is confirmed with 15N isotope labelling control experiments and it is attributed to a Mars-van Krevelen mechanism enabled by the formation of N-vacancies upon hydrogenation of surface nitrides. Chapter 6 reports on the interactions of adsorbing N and permeating H at the catalytic interface of nickel, iron and ruthenium based hydrogen permeable electrodes during electrolytic ammonia synthesis. In situ near ambient pressure X-ray photoelectron spectroscopy (XPS) is used to measure modifications in the surface electronic structure of the catalyst and the nature of the adsorbed molecules. This chapter shows that permeating atomic hydrogen reduces surface Ni oxide and hydroxide species, under conditions at which gaseous H2 does not. Moreover, the results demonstrate that the availability of surface Ni0 sites is a primary requirement for the chemisorption of gaseous N2. In situ XPS measurements reveal that nitrogen gas chemisorbs on the generated metallic sites, followed by hydrogenation via permeating H, as adsorbed N and NH3 are found on the Ni surface. Our findings indicate that the first hydrogenation step to NH and the last NH3 desorption step might be limiting at the utilised operating conditions. Finally, the study was then extended to Fe and Ru surfaces. However, the formation of surface iron oxide and nitride species on iron blocks the H permeation and prevents the reaction to advance; while on ruthenium the stronger Ru-N bond might favour the recombination of permeating hydrogen to H2 over the hydrogenation of adsorbed nitrogen. Chapter 7 provides a systematic investigation of the effect of operating temperature (in the range 25 to 120 °C) and H permeation flux on the N2 reduction reaction on Ni, leading to a considerably improved NH3 synthesis process. At 120 °C a stable operation was achieved for over 12 h with a 10 times higher cumulative NH3 production and almost 40-fold increase in faradaic efficiency compared to the room temperature operation reported in chapter 5. The results obtained in this chapter indicate that increasing operating temperatures enhances nitrogen adsorption and NH3 desorption, maintaining a steady N surface coverage throughout the NH3 synthesis cycle. Moreover, to operate the nitrogen reduction reaction in a stable and efficient manner, the control over the population of N, NHx and H species at the catalyst surface is critical, as well as the capability of oxides to be reduced by permeating H. As such, the adoption of H permeable electrodes allows to independently control the N activation and H permeation, by a large extent.@en

The electrochemical reduction of carbon dioxide (CO₂) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO₂. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO₂conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at -0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm², demonstrating the approach's potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

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The nitrogen reduction reaction (NRR) is a promising pathway toward the decarbonization of ammonia (NH3) production. However, unless practical challenges related to the detection of NH3 are removed, confidence in published data and experimental throughput will remain low for experiments in aqueous electrolyte. In this perspective, we analyze these challenges from a system and instrumentation perspective. Through our analysis we show that detection challenges can be strongly reduced by switching from an Hcell to a gas diffusion electrode (GDE) cell design as a catalyst testing platform. Specifically, a GDE cell design is anticipated to allow for a reduction in the cost of crucial 15N2 control experiments from €100−2000 to less than €10. A major driver is the possibility to reduce the 15N2 flow rate to less than 1 mL/min, which is prohibited by an inevitable drop in mass-transport at low flow rates in H-cells. Higher active surface areas and improved mass transport can further circumvent losses of NRR selectivity to competing reactions. Additionally, obstacles often encountered when trying to transfer activity and selectivity data recorded at low current density in Hcells to commercial device level can be avoided by testing catalysts under conditions close to those in commercial devices from the start.@en

Continued advancements in the electrochemical reduction of CO 2 (CO 2RR) have emphasized that reactivity,selectivity, and stability are not explicit material properties butcombined effects of the catalyst, double-layer, reaction environ-
ment, and system configuration. These realizations have steadily built upon the foundational work performed for a broad array of transition metals performed at 5 mA cm−2, which historically guided the research field. To encompass the changing advancements and mindset within the research field, an updated baseline at elevated current densities could then be of value. Here we seek to
re-characterize the activity, selectivity, and stability of the five most utilized transition metal catalysts for CO2 RR (Ag, Au, Pd, Sn, and Cu) at elevated reaction rates through electrochemical operation, physical characterization, and varied operating parameters to provide a renewed resource and point of comparison. As a basis, we have employed a common cell architecture, highly controlled catalyst layer morphologies and thicknesses, and fixed current densities. Through a dataset of 88 separate experiments, we provide comparisons between CO-producing catalysts (Ag, Au, and Pd), highlighting CO-limiting current densities on Au and Pd at 72 and 50 mA cm−2, respectively. We further show the instability of Sn in highly alkaline environments, and the convergence of product selectivity at elevated current densities for a Cu catalyst in neutral andalkaline media. Lastly, we reflect upon the use and limits of reaction rates as a baseline metric by comparing catalytic selectivity at 10
versus 200 mA cm−2. We hope the collective work provides a resource for researchers setting up CO 2RR experiments for the first time.@en

Hydrogen permeable electrodes can be utilized for electrolytic ammonia synthesis from dinitrogen, water, and renewable electricity under ambient conditions, providing a promising route toward sustainable ammonia. The understanding of the interactions of adsorbing N and permeating H at the catalytic interface is a critical step toward the optimization of this NH3 synthesis process. In this study, we conducted a unique in situ near ambient pressure X-ray photoelectron spectroscopy experiment to investigate the solid-gas interface of a Ni hydrogen permeable electrode under conditions relevant for ammonia synthesis. Here, we show that the formation of a Ni oxide surface layer blocks the chemisorption of gaseous dinitrogen. However, the Ni 2p and O 1s XPS spectra reveal that electrochemically driven permeating atomic hydrogen effectively reduces the Ni surface at ambient temperature, while H2 does not. Nitrogen gas chemisorbs on the generated metallic sites, followed by hydrogenation via permeating H, as adsorbed N and NH3 are found on the Ni surface. Our findings suggest that the first hydrogenation step to NH and the NH3 desorption might be limiting under the operating conditions. The study was then extended to Fe and Ru surfaces. The formation of surface oxide and nitride species on iron blocks the H permeation and prevents the reaction to advance; while on ruthenium, the stronger Ru-N bond might favor the recombination of permeating hydrogen to H2 over the hydrogenation of adsorbed nitrogen. This work provides insightful results to aid the rational design of efficient electrolytic NH3 synthesis processes based on but not limited to hydrogen permeable electrodes.

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The electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the current greenhouse gas emission intensive process to produce ammonia (NH₃) from nitrogen (N₂). However, finding an electrocatalyst that promotes NRR over the competing hydrogen evolution reaction (HER) has proven to be difficult. This difficulty could potentially be addressed by accelerating the electrocatalyst development for NRR by orders of magnitude using high-throughput (HTP) workflows. In this work, we developed a HTP gas diffusion electrode (GDE) cell to screen up to 16 electrocatalysts in parallel. The key innovation of the cell is the use of expanded Polytetrafluoroethylene (ePTFE) gas diffusion layers (GDL) which simplifies the handling of catalyst arrays compared to carbon fabrics and enables sufficient N₂ mass transport. We demonstrate the robustness of the HTP workflow by screening 528 bimetallic catalysts of composition AB (A,B = Ag, Al, Au, Co, Cu, Fe, Mn, Mo, Ni, Pd, Re, Ru, W) for NRR activity. None of the materials produced ammonia significantly over background level which emphasizes the difficulty of finding active electrocatalysts for NRR and narrows down the search space for future studies.

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Rapid advances in electrocatalytic ammonia synthesis are impeded by laborious detection methods commonly used in the field and by constant risk of external contaminations, which generates misleading false positives. We developed a facile real-time GC-MS method for sensitive isotope NH3 quantification, requiring no external sample manipulations. This method ensures high detection reliability paramount to accelerate (electro-)catalyst screening.@en

Direct electrochemical nitrogen reduction holds the promise of enabling the production of carbon emission-free ammonia, which is an important intermediate in the fertilizer industry and a potential green energy carrier. Here we show a strategy for ambient condition ammonia synthesis using a hydrogen permeable nickel membrane/electrode that spatially separates the electrolyte and hydrogen reduction side from the dinitrogen activation and hydrogenation sites. Gaseous ammonia is produced catalytically in the absence of electrolyte via hydrogenation of adsorbed nitrogen by electrochemically permeating atomic hydrogen from water reduction. Dinitrogen activation at the polycrystalline nickel surface is confirmed with 15N2 isotope labeling experiments, and it is attributed to a Mars-van Krevelen mechanism enabled by the formation of N-vacancies upon hydrogenation of surface nitrides. We further show that gaseous hydrogen does not hydrogenate the adsorbed nitrogen, strengthening the benefit of having an atomic hydrogen permeable electrode. The proposed approach opens new directions toward green ammonia.

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