Recent Advances in Nonprecious Metal Oxide Electrocatalysts and Photocatalysts for N2 Reduction Reaction under Ambient Condition

Conductive Metal-Organic Frameworks and Their Electrocatalysis Applications

Recently, electrically conductive metal-organic frameworks (EC-MOFs) have emerged as a wealthy library of porous frameworks with unique properties, allowing their use in diverse applications of energy conversion, including electrocatalysis. In this review, the electron conduction mechanisms in EC-MOFs are examined, while their electrical conductivities are considered. There have been various strategies to enhance the conductivities of MOFs including ligand modification, the incorporation of conducting materials, and the construction of multidimensional architectures. With sufficient conductivities being established for EC-MOFs, there have been extensive pursuits in their electrocatalysis applications, such as in the hydrogen evolution reaction, oxygen reduction reaction, oxygen evolution reaction, N2 reduction reaction, and CO2 reduction reaction. In addition, computational modeling of EC-MOFs also exerts an important impact on revealing the synthesis-structure-performance relationships. Finally, the prospects and current challenges are discussed to provide guidelines for designing promising framework materials.

Au-Added CuS Hollow Spheres to Regulate the Strength and Active Area of N2 Adsorption Sites for Electrochemical NH3 Production

Ammonia is a chemical compound in considerable global demand and plays a crucial role as an environmentally friendly energy carrier for hydrogen energy storage. The electrochemical nitrogen reduction reaction (eNRR) using copper sulfide catalysts is being extensively studied as an environmentally sustainable approach to the energy-intensive Haber-Bosch process for ammonia production. In this study, we aimed to prepare CuS hollow spheres modified with Au nanoparticles using an antisolvent crystallization-based method to be used as the catalysts for eNRR. During the addition of Au to the CuS catalysts, the nitrogen adsorption strength and surface area of the CuS catalysts are significantly regulated and expanded, leading to a noticeable enhancement in electrocatalytic performance for eNRR. Specifically, the ammonia production rate of 2.4 μmol cm-2 h or jNH3 = 0.2 mA cm-2 is achieved at a selectivity of 52% in neutral aqueous electrolyte, which is more than a 2-fold increase compared to the unmodified CuS catalyst. The findings of this study can contribute to the development of sustainable and environmentally friendly ammonia production in the future.

Research Progress on Ni-Based Electrocatalysts for the Electrochemical Reduction of Nitrogen to Ammonia

The electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia (NH3) is considered as a promising method due to its approvable advantages of zero-pollution emission, feasible reaction proceedings, good safety and easy management. The multiple efforts have been devoted to the exploration of earth-abundant-element-based nanomaterials as high-efficiency electrocatalysts for realizing their industrial applications. Among these, the Ni-based nanomaterials is prioritized as an attractive non-noble-metal electrocatalysts for catalyzing NRR because they are earth-abundance and exceedingly easy to synthesize as well as also delivers the potential of high electrocatalytic activity and durability. In this review, after briefly elucidating the underlying mechanisms of NRR during the electrochemical process, we systematically sum up the recent research progress in representative Ni-based electrocatalysts, including monometallic Ni-based nanomaterials, bimetallic Ni-based nanomaterials, polymetallic Ni-based nanomaterials, etc. In particular, we discuss the effects of physicochemical properties, such as phases, crystallinity, morphology, composition, defects, heteroatom doping, and strain engineering, on the comprehensive performance of the abovementioned electrocatalysts, with the aim of establishing the nanostructure-function relationships of the electrocatalysts. In addition, the promising directions of Ni-based electrocatalysts for NRR are also pointed out and highlighted. The generic approach in this review may expand the frontiers of NRR and provides the inspiration for developing high-efficiently Ni-based electrocatalysts.

Rational Design of Earth-Abundant Catalysts toward Sustainability

Catalysis is crucial for clean energy, green chemistry, and environmental remediation, but traditional methods rely on expensive and scarce precious metals. This review addresses this challenge by highlighting the promise of earth-abundant catalysts and the recent advancements in their rational design. Innovative strategies such as physics-inspired descriptors, high-throughput computational techniques, and artificial intelligence (AI)-assisted design with machine learning (ML) are explored, moving beyond time-consuming trial-and-error approaches. Additionally, biomimicry, inspired by efficient enzymes in nature, offers valuable insights. This review systematically analyses these design strategies, providing a roadmap for developing high-performance catalysts from abundant elements. Clean energy applications (water splitting, fuel cells, batteries) and green chemistry (ammonia synthesis, CO2 reduction) are targeted while delving into the fundamental principles, biomimetic approaches, and current challenges in this field. The way to a more sustainable future is paved by overcoming catalyst scarcity through rational design.

Photoelectrochemical Proton-Coupled Electron Transfer of TiO2 Thin Films on Silicon

TiO2 thin films are often used as protective layers on semiconductors for applications in photovoltaics, molecule-semiconductor hybrid photoelectrodes, and more. Experiments reported here show that TiO2 thin films on silicon are electrochemically and photoelectrochemically reduced in buffered acetonitrile at potentials relevant to photoelectrocatalysis of CO2 reduction, N2 reduction, and H2 evolution. On both n-type Si and irradiated p-type Si, TiO2 reduction is proton-coupled with a 1e-:1H+ stoichiometry, as demonstrated by the Nernstian dependence of the Ti4+/3+ E1/2 on the buffer pKa. Experiments were conducted with and without illumination, and a photovoltage of ∼0.6 V was observed across 20 orders of magnitude in proton activity. The 4 nm films are almost stoichiometrically reduced under mild conditions. The reduced films catalytically transfer protons and electrons to hydrogen atom acceptors, based on cyclic voltammogram, bulk electrolysis, and other mechanistic evidence. TiO2/Si thus has the potential to photoelectrochemically generate high-energy H atom carriers. Characterization of the TiO2 films after reduction reveals restructuring with the formation of islands, rendering TiO2 films as a potentially poor choice as protecting films or catalyst supports under reducing and protic conditions. Overall, this work demonstrates that atomic layer deposition TiO2 films on silicon photoelectrodes undergo both chemical and morphological changes upon application of potentials only modestly negative of RHE in these media. While the results should serve as a cautionary tale for researchers aiming to immobilize molecular monolayers on "protective" metal oxides, the robust proton-coupled electron transfer reactivity of the films introduces opportunities for the photoelectrochemical generation of reactive charge-carrying mediators.

Mechanistic insights into the electrolyte effects on the electrochemical nitrogen reduction reaction using copper hexacyanoferrate/f-MWCNT nano-composites

Developing an efficient, selective, and stable electrocatalysis system for the electrocatalytic N2 reduction reaction (ENRR) is a promising strategy for the green and sustainable production of ammonia. The activity, selectivity, and stability of various electrocatalysts in different electrolyte solvents, mainly acidic and alkaline electrolytes, are commonly compared in the literature. However, a mechanistic insight into the effect of these electrolytes on ENRR activity is lacking. Herein we demonstrate that the acidity or alkalinity of the electrolyte is a key factor in determining the rate-limiting step and, by extension, the ENRR performance of an electrochemical setup for the electroproduction of ammonia. Our results from ex situ X-ray photoelectron, Raman, and FTIR spectroscopy analysis of the fresh and spent Cu-hexacyanoferrate Prussian blue analogue-decorated functionalized carbon nanotube (CuFe PBA/f-CNT) catalyst reveal that NH4+-species are more strongly adsorbed on the catalyst surface during the ENRR in acidic than in alkaline electrolytes. The results of our detailed rotating ring-disc electrode voltammetry studies suggest that the ENRR over CuFe PBA/f-CNT is mostly controlled by surface adsorption in an acidic electrolyte and by mass transport in an alkaline electrolyte. In situ Raman spectroscopy confirms this finding and shows that the leaching of Fe(CN)6 species from the CuFe PBA/f-CNT composite in an alkaline electrolyte greatly affects the ENRR performance. We believe that the work presented herein offers a new insight into the mechanistic aspects of the ENRR in different electrolyte systems and hence can prove very valuable for the development of effective ENRR electrode/electrolyte systems for practical applications.

Exploring Metal Nanocluster Catalysts for Ammonia Synthesis Using Informatics Methods: A Concerted Effort of Bayesian Optimization, Swarm Intelligence, and First-Principles Computation

This paper details the use of computational and informatics methods to design metal nanocluster catalysts for efficient ammonia synthesis. Three main problems are tackled: defining a measure of catalytic activity, choosing the best candidate from a large number of possibilities, and identifying the thermodynamically stable cluster catalyst structure. First-principles calculations, Bayesian optimization, and particle swarm optimization are used to obtain a Ti8 nanocluster as a catalyst candidate. The N2 adsorption structure on Ti8 indicates substantial activation of the N2 molecule, while the NH3 adsorption structure suggests that NH3 is likely to undergo easy desorption. The study also reveals several cluster catalyst candidates that break the general trade-off that surfaces that strongly adsorb reactants also strongly adsorb products.

Atomic-scale insights into the interfacial charge transfer in a NiO/CeO2 heterostructure for electrocatalytic hydrogen evolution

To understand the underlying mechanism of the interfacial charge transfer and local chemical state variation in the nonprecious-based hydrogen evolution reaction (HER) electrocatalysts, a model system of the NiO/CeO₂ heterostructure was chosen for investigation using a combination of the advanced electron microscopic characterization and first-principles calculations. The results directly proved that interfacial charge transfer occurs from Ni to Ce, leading to reduction in the valence state of Ce and increased formation of V_O. This would optimize ΔG_H* and facilitate the hydrogen evolution process, resulting in outstanding HER performance in 1 M KOH with a low overpotential of 99 mV at the current density of 10 mA•cm^-2 and a modest Tafel slope of 78.4 mV•dec^-1 for the NiO/CeO₂ heterostructure sample. Therefore, the improved HER performance could be attributed to the synergistic coupling interactions and electron redistribution at the interface of NiO and CeO₂. These results concretely demonstrate the direct determination of the interfacial structure of the heterostructure and provide atomistic insights to unravel the underlying mechanism of interfacial charge transfer induced HER performance improvement.

MOFs-derived plum-blossom-like junction In/In2O3@C as an efficient nitrogen fixation photocatalyst: Insight into the active site of the In3+ around oxygen vacancy

Nitrogen activation with low-cost, visible-light-driven photocatalysts continues to be a major challenge. Since the discovery of biological nitrogen fixation, multi-component systems have achieved higher efficiency due to the synergistic effects, thus one of the challenges has been distinguishing the active sites in multi-component catalysts. In this study, we report the photocatalysts of In/In2O3@C with plume-blossom-like junction structure obtained by one-step roasting of MIL-68-In. The "branch" is carbon for supporting and protecting the structure, and the "blossom" is In/In2O3 for the activation and reduction of N2, which form an efficient photocatalyst for nitrogen fixation reaction with the performance of 51.83 μmol h-1 g-1. Experimental studies and DFT calculations revealed the active site of the catalyst for nitrogen fixation reaction is the In3+ around the oxygen vacancy in In2O3. More importantly, the elemental In forms the Schottky barrier with In2O3 in the catalyst, which can generate a built-in electric field to form charge transfer channels during the photocatalytic activity, not only broadens the light absorption range of the material, but also exhibits excellent metal conductivity.

Nanoscale Measurements of Charge Transfer at Cocatalyst/Semiconductor Interfaces in BiVO4 Particle Photocatalysts

Semiconductor photocatalyst particles convert solar energy to fuels like H₂. The particles are often assumed to provide crystalline-facet-dependent electron-hole separation. A common strategy is to deposit a hydrogen evolution reaction (HER) electrocatalyst on electron-selective facets and an oxygen evolution reaction (OER) electrocatalyst on hole-selective facets. A precise understanding of how charge-carrier-selective contacts emerge and how they are rationally designed, however, is missing. Using a combination of ex situ and in situ conducting atomic force microscopy (AFM) experiments and new ionomer/catalyst-semiconductor test structures, we show how heterogeneity in charge-carrier selectivity can be measured at the nanoscale. We discover that the presence of the water/electrolyte interface is critical to induce hole selectivity between the CoO_x water-oxidation catalyst and the BiVO₄ light absorber. pH-dependent measurements suggest that negative surface charge on the semiconductor is central to inducing hole selectivity. The work also demonstrates a new approach to control local pH and introduce water using thin-film ionomers compatible with conductive AFM measurements.

Coordination-induced bond weakening of water at the surface of an oxygen-deficient polyoxovanadate cluster

Hydrogen-atom (H-atom) transfer at the surface of heterogeneous metal oxides has received significant attention owing to its relevance in energy conversion and storage processes. Here, we present the synthesis and characterization of an organofunctionalized polyoxovanadate cluster, (calix)V6O5(OH2)(OMe)8 (calix = 4-tert-butylcalix[4]arene). Through a series of equilibrium studies, we establish the BDFE(O-H)avg of the aquo ligand as 62.4 ± 0.2 kcal mol-1, indicating substantial bond weaking of water upon coordination to the cluster surface. Subsequent kinetic isotope effect studies and Eyring analysis indicate the mechanism by which the hydrogenation of organic substrates occurs proceeds through a concerted proton-electron transfer from the aquo ligand. Atomistic resolution of surface reactivity presents a novel route of hydrogenation reactivity from metal oxide surfaces through H-atom transfer from surface-bound water molecules.

PdFe Single-Atom Alloy Metallene for N2 Electroreduction

Single-atom alloys hold great promise for electrocatalytic nitrogen reduction reaction (NRR), while the comprehensive experimental/theoretical investigations of SAAs for the NRR are still missing. Herein, PdFe₁ single-atom alloy metallene, in which the Fe single atoms are confined on a Pd metallene support, is first developed as an effective and robust NRR electrocatalyst, delivering exceptional NRR performance with an NH₃ yield of 111.9 μg h^-1  mg^-1 , a Faradaic efficiency of 37.8 % at -0.2 V (RHE), as well as a long-term stability for 100 h electrolysis. In-depth mechanistic investigations by theoretical computations and operando X-ray absorption/Raman spectroscopy indentify Pd-coordinated Fe single atoms as active centers to enable efficient N₂ activation via N₂ -to-Fe σ-donation, reduced protonation energy barriers, suppressed hydrogen evolution and excellent thermodynamic stability, thus accounting for the high activity, selectivity and stability of PdFe₁ for the NRR.

Transition Metals Embedded Two-Dimensional Square Tetrafluorotetracyanoquinodimethane Monolayers as a Class of Novel Electrocatalysts for Nitrogen Reduction Reaction

The combination of transition metal (TM) atoms and high electron affinity organic framework tetrafluorotetracyanoquinodimethanes (F₄TCNQs) makes the TM-embedded two-dimensional (2D) square F₄TCNQ monolayers (TM-sF₄TCNQ) possible to have excellent characteristics of single-atom catalysts and 2D materials. For the first time, the TM-sF₄TCNQ monolayers have been considered for application in the electrocatalytic nitrogen reduction reaction (eNRR) field. Through high-throughput screening, the catalytic performance of 30 TM-sF₄TCNQ (TM = 3d∼5d TMs) monolayers for eNRR was comprehensively evaluated. The Mo-, Nb-, and Tc-sF₄TCNQ catalysts stand out with the onset potentials of -0.18, -0.44, and -0.54 V, respectively, through the optimal reaction paths. Our work will provide guidance for the green and sustainable development of electrocatalytic nitrogen fixation.

Recent advances and challenges in 2D/2D heterojunction photocatalysts for solar fuels applications

Although photocatalytic technology has emerged as an effective means of alleviating the projected future fuel crisis by converting sunlight directly into chemical energy, no visible-light-driven, low-cost, and highly stable photocatalyst has been developed to date. Due to considerably higher interfacial contact with numerous reactive sites, effective charge transmission and separation ability, and strong redox potentials, the focus has now shifted to 2D/2D heterojunction systems, which have exhibited effective photocatalytic performance. The fundamentals of 2D/2D photocatalysis for different applications and the classification of 2D/2D materials are first explained in this paper, followed by strategies to improve the photocatalytic performance of various 2D/2D heterojunction systems. Following that, current breakthroughs in 2D/2D metal-based and metal-free heterojunction photocatalysts, as well as their applications for H₂ evolution via water splitting, CO₂ reduction, and N₂ fixation, are discussed. Finally, a brief overview of current constraints and predicted results for 2D/2D heterojunction systems is also presented. This paper lays out a strategy for developing efficient 2D/2D heterojunction photocatalysts and sophisticated technology for solar fuel applications in order to address the energy issue.

Copper Particle-Enhanced Lithium-Mediated Synthesis of Green Ammonia from Water and Nitrogen

Ammonia (NH₃) is one of the most frequently produced chemical products in the world, and it plays an indispensable role in life on Earth. However, its synthesis by the Haber-Bosch (H-B) process is highly energy intensive, resulting in extensive carbon emissions that are unsustainable due to their ability to harm the environment. Herein, we propose a facile and mass-producible strategy for increasing the rate and efficiency of nitrogen fixation through the use of copper particle-catalyzed Li nitridation and a solid electrolyte as a medium to reduce Li salt; the above strategy results in the conversion of water and nitrogen into NH₃ through the use of renewable electrical energy at room temperature and atmospheric pressure. Copper particles are uniformly pressed into Li metal by a simple rolling method, and their critical role in accelerating the nitrogen fixation process is revealed by both electrochemical tests and simulations. The nitridation of the Li in the composite is reduced to a few minutes instead of the more than 40 h that are needed for bare Li and N₂ at room temperature and atmospheric pressure. Our new method provides three important advantages over the H-B method: (1) the new method can be operated at atmospheric pressure, thereby lowering equipment requirements and increasing security; (2) the use of water instead of fossil fuels as a hydrogen source decreases the consumption of these fuels and the emission of CO₂; and (3) the low equipment requirements lead to the ready miniaturization and decentralization of the NH₃ synthesizing process, thus promoting the possible use of renewable sources of electricity (e.g., wind or solar energy).

Highly Active and Selective Electroreduction of N2 by the Catalysis of Ga Single Atoms Stabilized on Amorphous TiO2 Nanofibers

The electroreduction of N₂ under ambient conditions has emerged as one of the most promising technologies in chemistry, since it is a greener way to make NH₃ than the traditional Haber-Bosch process. However, it is greatly challenged with a low NH₃ yield and faradaic efficiency (FE) because of the lack of highly active and selective catalysts. Inherently, transition (d-block) metals suffer from inferior selectivity due to fierce competition from H₂ evolution, while post-transition (p-block) metals exhibit poor activity due to insufficient "π back-donation" behavior. Considering their distinct yet complementary electronic structures, here we propose a strategy to tackle the activity and selectivity challenge through the atomic dispersion of p-block metal on an all-amorphous transition-metal matrix. To address the activity issue, lotus-root-like amorphous TiO₂ nanofibers are synthesized which, different from vacancy-engineered TiO₂ nanocrystals reported previously, possess abundant intrinsic oxygen vacancies (V_O) together with under-coordinated dangling bonds in nature, resulting in significantly enhanced N₂ activation and electron transport capacity. To address the selectivity issue, well-isolated single atoms (SAs) of Ga are successfully synthesized through the confinement effect of V_O, resulting in Ga-V_O reactive sites with the maximum availability. It is revealed by density functional theory calculations that Ga SAs are favorable for the selective adsorption of N₂ at the catalyst surface, while V_O can facilitate N₂ activation and reduction subsequently. Benefiting from this coupled activity/selectivity design, high NH₃ yield (24.47 μg h^-1 mg^-1) and FE (48.64%) are achieved at an extremely low overpotential of -0.1 V vs RHE.

Metal-free BN quantum dots/graphitic C3N4 heterostructure for nitrogen reduction reaction

Exploring high-efficiency metal-free electrocatalysts towards N₂ reduction reaction (NRR) is of great interest for the development of electrocatalytic N₂ fixation technology. Herein, we combined boron nitride quantum dots (BNQDs) and graphitic carbon nitride (C₃N₄) to design a metal-free BNQDs/C₃N₄ heterostructure as an effective and durable NRR catalyst. The electronically coupled BNQDs/C₃N₄ presented an NH₃ yield as high as 72.3 μg h^-1 mg^-1 (-0.3 V) and a Faradaic efficiency of 19.5% (-0.2 V), far superior to isolated BNQDs and C₃N₄, and outperforming nearly all previously reported metal-free catalysts. Theoretical computations unveiled that the N₂ activation could be drastically enhanced at the BNQDs-C₃N₄ interface where interfacial BNQDs and C₃N₄ cooperatively adsorb N₂ and stabilize *N₂H intermediate, leading to the significantly promoted NRR process with an ultra-low overpotential of 0.23 V.

Recent advances in MoS2-based materials for electrocatalysis

The increasing energy demand and related environmental issues have drawn great attention of the world, thus necessitating the development of sustainable technologies to preserve the ecosystems for future generations. Electrocatalysts...

Ultrasmall iridium nanoparticles on graphene for efficient nitrogen reduction reaction

Ultrasmall iridium nanoparticles on reduced graphene oxide (Ir/RGO) exhibited a high NRR activity, attributed to the RGO-induced upshifting of the d-band center for active Ir sites, leading to decreased NRR energy barriers.

Increasing Oxygen Vacancy of CeO2 Nanocrystals by Ni Doping and reduced Graphene Oxides Decoration towards the Electrocatalytic Hydrogen Evolution

The oxygen vacancy (VO) engineering is proved to be an effective approach for improving the hydrogen evolution reaction (HER) performance of low-cost metal oxides electrocatalysts. Cerium dioxide (CeO2), one of...

Understanding the Z-scheme heterojunction of BiVO4/PANI for photoelectrochemical nitrogen reduction

Based on the idea that a heterojunction can significantly promote photoelectrochemical (PEC) efficiency, BiVO₄/PANI (polyaniline), as a Z-scheme heterojunction, was designed in this work. BiVO₄/PANI achieved a desirable NH₃ yield rate (r_NH3 = 0.93 μg h^-1 cm^-2) and faradaic efficiency (FE = 26.43%). This study presents novel insight into PEC NRR research, and it could be extended to the modification of other catalysts for boosting PEC N₂ reduction reaction performance.

Synergistic Enhancement of Electrocatalytic Nitrogen Reduction Over Boron Nitride Quantum Dots Decorated Nb2 CTx -MXene

Electrochemical N₂ fixation represents a promising strategy toward sustainable NH₃ synthesis, whereas the rational design of high-performance catalysts for the nitrogen reduction reaction (NRR) is urgently required but remains challenging. Herein, a novel hexagonal BN quantum dots (BNQDs) decorated Nb₂ CT_x -MXene (BNQDs@Nb₂ CT_x ) is explored as an efficient NRR catalyst. BNQDs@Nb₂ CT_x presents the optimum NRR activity with an NH₃ yield rate of 66.3 µg h^-1 mg^-1 (-0.4 V) and a Faradaic efficiency of 16.7% (-0.3 V), outperforming most of the state-of-the-art NRR catalysts, together with an excellent stability. Theoretical calculations revealed that the synergistic interplay of BNQDs and Nb₂ CT_x enabled the creation of unique interfacial B sites serving as NRR catalytic centers capable of enhancing the N₂ activation, lowering the reaction energy barrier and impeding the H₂ evolution.

MoS2 quantum dots for electrocatalytic N2 reduction

We demonstrate that MoS₂ quantum dots (QDs) can be an effective and durable catalyst for the electrocatalytic N₂ reduction reaction (NRR), showing an NH₃ yield of 39.6 μg h^-1 mg^-1 with a faradaic efficiency of 12.9% at -0.3 V, far superior to MoS₂ nanosheets and outperforming most reported NRR catalysts. Density functional theory computations unravel that the MoS₂ QDs can dramatically facilitate N₂ adsorption and activation via side-on patterns, resulting in an energetically-favored enzymatic pathway with an ultra-low overpotential of 0.29 V.

Double boron atom-doped graphdiynes as efficient metal-free electrocatalysts for nitrogen reduction into ammonia: a first-principles study

The electroreduction of dinitrogen (N₂) is an attractive method for ambient ammonia (NH₃) synthesis. In this work, double boron atom-anchored two-dimensional (2D) graphdiyne (GDY-2B) electrocatalysts have been designed and examined for the N₂ reduction reaction (NRR) by density functional theory computations. Our calculations revealed that double boron atoms can be strongly embedded in a graphdiyne monolayer. In particular, configuration GDY-2B(S₂S₂') with two boron atoms substituting two equivalent sp-carbon atoms of diacetylene linkages exhibits excellent catalytic performance for reducing N₂, with an extremely low overpotential of 0.12 V. The "pull-pull" mechanism imposed by doped double boron atoms is responsible for the magnificent effect of N₂ activation. Besides, the competitive reaction of the hydrogen evolution reaction (HER) is suppressed owing to a large ΔG_H* value of -1.25 eV. Based on these results, our study provides useful guidelines for designing effective double atomic catalysts (DACs) based on nonmetal 2D nanosheets for effective electrochemical reduction reactions.

Identifying the Dominant Role of Pyridinic-N-Mo Bonding in Synergistic Electrocatalysis for Ambient Nitrogen Reduction

For electrochemical nitrogen reduction reaction (NRR), hybridizing transition metal (TM) compounds with nitrogen-doped carbonaceous materials has been recognized as a promising strategy to improve the activity and stability of electrocatalysts due to the synergistic interaction from the TM-N-C active sites. Nevertheless, up to date, the fundamental mechanism of this so-called synergistic electrocatalysis for NRR is still unclear. Particularly, it remains ambiguous which configuration of N dopants, either pyridinic N or pyrrolic N, when coordinated with the TM, predominately contributes to this synergy. Herein, a self-assembled three-dimensional 1T-phase MoS₂ microsphere coupled with N-doped carbon was developed (termed MoS₂/NC), showing an impressive NRR performance in neutral medium. The hybridization of MoS₂ and N-doped carbon can synergistically enhance the NRR efficiency by optimizing the electron transfer of catalyst. Acidification/blocking/poisoning experiments reveal the decisive role of pyridinic-N-Mo bonding, rather than pyrrolic-N-Mo bonding, in synergistically enhancing NRR electrocatalysis. The electrochemical-based in situ Fourier transform infrared spectroscopy (in situ FTIR) technology provides deep insights into the substantial contribution of pyridinic-N-MoS₂ sites to NRR electrocatalysis and further uncover the underlying mechanism (associative pathway) at a molecular level.

Efficient Electrocatalytic N2 Reduction on Three-Phase Interface Coupled in a Three-Compartment Flow Reactor for the Ambient NH3 Synthesis

The electrochemical N₂ reduction reaction (eNRR) represents a carbon-free alternative to the Haber-Bosch process for a sustainable NH₃ synthesis powered by renewable energy under ambient conditions. Despite significant efforts to develop catalyst activity and selectivity toward eNRR, an appropriate electrochemical system to obstruct the drawback of low N₂ solubility remains broadly unexplored. Here, we demonstrate an electrocatalytic system combining a ruthenium/carbon black gas diffusion electrode (Ru/CB GDE) with a three-compartment flow cell, enabling solid-liquid-gas catalytic interfaces for the highly efficient Ru-catalyzed eNRR. The electrolyte optimization and the Ru/CB GDE development through the hydrophobicity, the Ru/CB loading, and the post-treatment have revealed the crucial contribution of interfacial N₂ transportation and local pH environment. The optimized hydrophobic Ru/CB GDE generated excellent eNRR performance, achieving a high NH₃ yield rate of 9.9 × 10^-10 mol/cm² s at -0.1 V vs RHE, corresponding to the highest faradaic efficiency of 64.8% and a specific energy efficiency of 40.7%, exceeding the most reported system. This work highlights the critical role of design and optimization of the GDE-flow cell combination and provides a valuable practicable solution to enhance the electrochemical reaction involving gas-phase reactants with low solubility.

Electrochemical nitrogen reduction: recent progress and prospects

Ammonia is one of the most useful chemicals for the fertilizer industry and is also promising as an important energy carrier for fuel cell application, and is currently mostly produced by the traditional Haber-Bosch process under high temperature and pressure conditions. This energy-intensive process is detrimental to the environment due to the dependence on fossil fuels and the emission of significant greenhouse gases (such as CO2). Ammonia production via the electrochemical nitrogen reduction reaction (ENRR) has been recognized as a green sustainable alternative to the Haber-Bosch process in recent years. Current ENRR research mainly focuses on the catalyst for ammonia selective production and the enhancement of faradaic efficiency at high current density; however, these have not been explored well due to the unavailability of highly efficient and cheap catalysts. Herein, this review provides information on the ENRR process along with (i) theoretical background, (ii) experimental methodology of the electrocatalytic process and (iii) computational screening of promising catalysts. The impact of active sites and defects on the activity, selectivity, and stability of the catalysts is deeply understood. Furthermore, we demonstrate the mechanistic understanding of the ENRR process on the surface of catalysts, with the aim of boosting the improvement of the ENRR activities. The ammonia detection methods are also summarized along with thorough discussion of control experiments. Finally, this review highlights prevailing problems in existing ENRR methods of ammonia production along with technical advancements proposed to address these issues and concludes with comments on opportunities and future directions of the ENRR process.

An amorphous WC thin film enabled high-efficiency N2 reduction electrocatalysis under ambient conditions

Ambient electrochemical N2 reduction offers a promising alternative to the energy-intensive Haber-Bosch process towards renewable NH3 synthesis in aqueous media but needs efficient electrocatalysts to enable the N2 reduction reaction (NRR). Herein, we propose that an amorphous WC thin film magnetron sputtered onto a graphite foil behaves as a superb NRR electrocatalyst for ambient NH3 production with excellent selectivity. In 0.5 M LiClO4, it attains a large NH3 yield of 43.37 μg h-1 mg-1cat. and a high faradaic efficiency of 21.65% at -0.10 V vs. reversible hydrogen electrode. Impressively, this catalyst also shows excellent selectivity and strong durability for NH3 formation.

YF3: a nanoflower-like catalyst for efficient nitrogen fixation to ammonia under ambient conditions

Ammonia as a vital chemical is not only indispensable to agriculture but also crucial to some energy devices like fuel cells.

CuS concave polyhedral superstructures enabled efficient N2 electroreduction to NH3 at ambient conditions

CuS concave polyhedral superstructures with high symmetry offer an appealing V_NH3 of 18.18 μg h⁻¹ mg⁻¹_cat. and a faradaic efficiency of 5.63% at −0.15 V vs. RHE in 0.1 M HCl.