Electrochemical Nitrogen Reduction Reaction Research Articles

Paradox of thiourea: A false-positive and promoter for electrochemical nitrogen reduction on nickel sulfide catalysts

Electrochemical nitrogen reduction reaction (NRR) is an environmentally friendly process for ammonia synthesis. An unusually high NH3 production rate (86.91 ± 9.29 μg h−1 cm−2) and Faradaic efficiency (F.E.) (57.17 ± 4.14 %) was observed in electrochemical tests on NiS catalysts synthesized using thiourea (TU). Through joint experiment-theory work, we demonstrate the paradoxical catalytic effect of TU as a false positive from TU-derived thiocyanate reduction and a promoter via the generation of catalytically active carbon sites after TU reduction on the NiS surface (with an effective NH3 rate of 52 ± 5.57 μg h−1 cm−2). TU reduction leads to the substitution of an S atom to a reactive C atom with fewer valence electrons, facilitating a more facile NRR pathway. This study presents a new possibility for NRR catalysts based on metal-nonmetal compounds (e.g., sulfides, chalcogenides, or nitrides) by nonmetal dopants with fewer valence electrons to create new catalytically active sites.

A High-Throughput Screening toward Efficient Nitrogen Fixation: Transition Metal Single-Atom Catalysts Anchored on an Emerging π-π Conjugated Graphitic Carbon Nitride (g-C10N3) Substrate with Dirac Dispersion.

TM-Nx is becoming a comforting catalytic center for sustainable and green ammonia synthesis under ambient conditions, resulting in increasing interest in single-atom catalysts (SACs) for the electrochemical nitrogen reduction reaction (NRR). However, given the poor activity and unsatisfactory selectivity of existing catalysts, it remains a long-standing challenge to design efficient catalysts for nitrogen fixation. Currently, the two-dimensional (2D) graphitic carbon-nitride substrate provides abundant and evenly distributed holes for stably supporting transition-metal atoms, which presents a fascinating prospect for overcoming this challenge and promoting single-atom NRR. An emerging holey graphitic carbon-nitride skeleton with a C10N3 stoichiometric ratio (g-C10N3) from a supercell of graphene is constructed, which provides outstanding electric conductivity for achieving high-efficiency NRR due to the Dirac band dispersion. Herein, a high-throughput first-principles calculation is carried out to evaluate the feasibility of π-d conjugated SACs resulting from a single TM atom anchored on g-C10N3 (TM = Sc-Au) for NRR. We find that W metal embedded in g-C10N3 (W@g-C10N3) can compromise the ability to adsorb the key target reaction species (N2H and NH2), hence acquiring an optimal NRR behavior among 27 TM-candidates. Our calculations demonstrate that W@g-C10N3 shows a well-suppressed HER ability and, impressively, a low energy cost of -0.46 V. Additionally, all-around descriptors are proposed to uncover the fundamental mechanism of NRR activity, among which a 3D volcano plot (limiting potential, screening strategy, and electron origin) uncovers the NRR activity trend, achieving a quick and high-efficiency prescreening for numerous candidates. Overall, the strategy of the structure- and activity-based TM-Nx-containing unit design will offer useful insight for further theoretical and experimental attempts.

Newly designed photocatalyst of Fe4 single clusters on g-C6N6 for nitrogen reduction reaction

The current industrial synthesis of ammonia proceeds through Haber–Bosch process, in which the adsorbed N2 are directly dissociated, and the reaction is limited by Brønsted–Evans–Polanyi (BEP) relation. In this work, the catalytic properties of Fe4 clusters fixed on g-C6N6 for nitrogen reduction reaction (NRR) are explored by first-principle calculations. The studies on the structural stability, adsorption capacity for N2 and the change of Gibbs free energy proves that Fe4 cluster catalyst exhibits excellent catalytic activity and high selectivity for NRR. The “acceptance-donation” interaction between Fe4@g-C6N6 and N atoms presented by PDOS and Bader charge analysis will facilitate the breaking of NN bonds. The 100 % Faraday efficiency further proves the high NRR selectivity. The results provide an effective strategy for designing high-performance electrochemical NRR catalysts.

Disordered Au Nanoclusters for Efficient Ammonia Electrosynthesis.

The electrochemical nitrogen (N2 ) reduction reaction (N2 RR) under mild conditions is a promising and environmentally friendly alternative to the traditional Haber-Bosch process with high energy consumption and greenhouse emission for the synthesis of ammonia (NH3 ), but high-yielding production is rendered challenging by the strong nonpolar N≡N bond in N2 molecules, which hinders their dissociation or activation. In this study, disordered Au nanoclusters anchored on two-dimensional ultrathin Ti3 C2 Tx MXene nanosheets are explored as highly active and selective electrocatalysts for efficient N2 -to-NH3 conversion, exhibiting exceptional activity with an NH3 yield rate of 88.3±1.7 μg h-1 mgcat. -1 and a faradaic efficiency of 9.3±0.4 %. A combination of in situ near-ambient pressure X-ray photoelectron spectroscopy and operando X-ray absorption fine structure spectroscopy is employed to unveil the uniqueness of this catalyst for N2 RR. The disordered structure is found to serve as the active site for N2 chemisorption and activation during the N2 RR process.

Complementary Design in Multicomponent Electrocatalysts for Electrochemical Nitrogen Reduction: Beyond the Leverage in Activity and Selectivity.

Electrochemical nitrogen reduction reaction (eNRR) is promising in place of the Haber-Bosch process for artificial N2 fixation. However, the high activity and selectivity of eNRR are challenging to achieve simultaneously due to the scaling relations. Such "leverage" between activity and selectivity has severely restricted eNRR. To overcome this bottleneck, the complementary design of electronic structures in multicomponent electrocatalysts has been recently pursued, aiming to maximize the advantages of each component and optimize the multistep reactions, which has stood at the cutting edge in this aspect. Here, we present a minireview of the design, performance, and mechanism of multicomponent electrocatalysts with complementary electronic structures. We particularly emphasize the interactions between N2 and elements from d-, p-, and s-blocks, which are essential for understanding how these electrocatalysts are beyond the "leverage" between activity and selectivity.

TiO2/CeO2 Frame with Enriched Oxygen Vacancies and Hetero‐Interfaces for Efficient Electrochemical N2 Reduction

AbstractElectrochemical nitrogen reduction reaction (NRR) under ambient conditions offers an environmentally benign and sustainable alternative for NH3 synthesis. Exploring highly active and robust NRR electrocatalysts is one of the prerequisites for developing sustainable N2/NH3 cycle systems. In this work, a surface chemistry rich TiO2/CeO2 frame is developed for electrochemical NRR, which is composed of ultrathin TiO2 nanosheets supported with CeO2 nanoparticles. Its unique porous framework as well as formed plentiful oxygen vacancies (OVs) and hetero‐interfaces collectively facilitate the adsorption/activation of N2 and transfer of electrons and protons. The catalyst can attain a high NH3 yield rate of 8.8 μg h−1 mg−1cat. and a Faradaic efficiency of 6.8 % at −0.25 V versus reversible hydrogen electrode, comparable with other reported Ti‐based and OVs‐contained catalysts. Moreover, the TiO2/CeO2 can maintain high durability over repeated 20 cycles. Therefore, this work heralds a new paradigm of fabricating framework‐structured catalyst with enriched hetero‐interfaces and defects toward effective and sustainable NH3 synthesis.

Electrocatalytic nitrogen fixation performance of two-dimensional Metal-Organic Frameworks Cu3(C6O6) and TM/Cu3(C6O6) from first-principle study

Electrochemical nitrogen reduction reaction can convert N2 into NH3 under ambient conditions, which is a friendly method of ammonia synthesis. Many studies have shown that two-dimensional Metal-Organic Framework (2D-MOF) materials have potential applications in the field of catalysis. In this paper, we systematically studied different single-atom catalysts (SACs) TM/Cu3(C6O6) by the density functional theory (DFT), and screened out two suitable candidate catalysts. Fe/Cu3(C6O6) and Co/Cu3(C6O6) catalysts have the excellent catalytic activity with the limiting potentials of −0.92 V and −0.97 V respectively. And it reveals that doping transition metal atoms can effectively improve the catalytic activity of Cu3(C6O6). Interestingly, we analyzed the electronic band structures and the density of state (DOS) of the catalysts, the results show that they have metallic properties and have good electrical conductivity. Therefore, Fe/Cu3(C6O6) and Co/Cu3(C6O6) are promising catalysts for NRR. Our study provides a new idea for the design of high-efficiency nitrogen reduction catalysts.

Screening of single-atom catalysts of transition metal supported on MoSe2 for high-efficiency nitrogen reduction reaction

Two-dimensional single-atom catalysts (2D SACs) have attracted much more attention in the field of ammonia synthesis via electrochemical nitrogen reduction reaction (NRR). In this work, we comprehensively study the NRR performance of 28 transition metals SACs loaded on 2D MoSe2 using density functional theory calculations. In view of thermodynamics and electrochemical stability, adsorption of N2, selectivity and activity of NRR, Mn, Os, V@MoSe2 exhibit outstanding performances with the most favorable potentials of -0.39 V, -0.36 V and -0.36 V, respectively. The excellent NRR performances are comprehensively related to the electronic states, kinetics, and NN bond length. Furthermore, aiming at three vital processes of NRR (adsorption and activation of N2, adsorption strength of intermediates, and the limiting potential), three independent descriptors (φ, ICOHP, ΔG*N) are adopted to make the activity trend clear. The results are of guiding significance to the design of high-efficiency NRR using SAC.

Two-Dimensional Ordered Double-Transition Metal Carbides for the Electrochemical Nitrogen Reduction Reaction

The electrochemical nitrogen reduction reaction (NRR) provides a green and sustainable strategy as an alternative to the Haber-Bosch process. The development of electrocatalysts with low overpotential, high selectivity, and fast reaction kinetics remains a significant challenge. Here, density functional theory computations are carried out to systematically predict the prospect of 18 two-dimensional (2D) ordered double-transition metal carbides (MXenes) as NRR electrocatalysts. Our results revealed that the basal plane of Mo2Nb2C3 MXene exhibited the most outstanding catalytic activity while effectively suppressed the hydrogen evolution reaction with an overpotential of 0.48 V. The exposed Mo3 moiety moderately regulating the electron transfer between reaction intermediates is answerable for the high activity. Finally, our finding broadens the horizon of 2D materials as NRR electrocatalysts.

Recent Progress in Electrochemical Nitrogen Reduction on Transition Metal Nitrides.

Distributed electrochemical nitrogen reduction reaction (ENRR) powered by renewable energy for the on-site production of ammonia is an attractive alternative to the industrial Haber-Bosch process, which is responsible for roughly 2 % of global energy consumption. In this Review, we summarize recent progress in the ENRR catalyzed by transition metal nitrides (TMNs). The unique electronic structures of TMNs make them promising ENRR catalysts for active and selective ammonia production, which have been predicted theoretically and demonstrated experimentally. Reaction pathways and deactivation mechanisms of the ENRR on different TMNs are surveyed, and current understanding of structure-activity relations is discussed. To develop highly active, selective, and stable TMN catalysts for industrial-scale ENRR, membrane electrode assembly configuration is recommended in catalyst evaluation. Furthermore, we highlight the importance of developing mechanistic understanding on ENRR with different operando spectroscopic techniques.

First-principles study of noble metal atom doped Fe(100) as electrocatalysts for nitrogen reduction reaction

NH3 is one of the most important chemicals on earth and can be used as a chemical feedstock, agricultural fertilizer and hydrogen-rich carrier. Recently, the technology of NH3 synthesis by electrochemical nitrogen reduction reaction (NRR) has attracted extensive attention. The core problem of the NRR is the development of electrocatalysts with high activity, selectivity and stability. Fe is not only a constituent element of biological nitrogenase, but also a widely used catalyst material in industrial NH3 synthesis. Due to the presence of unoccupied orbitals, it shows some potential in the process of N2 adsorption and desorption. Therefore, the catalytic activity of Fe(100) for the NRR was studied based on density functional theory, and the electronic properties of Fe(100) were regulated by doping noble metal (NM= Ru, Rh, Pd, Os, Ir, Pt) atoms to reduce the energy barrier and enhance the activity and selectivity of the catalyst. Through the screening of three important processes including N2 adsorption and activation, N2H formation and NH3 desorption, the catalytic activity of Ir atom doped Fe(100) (Ir@Fe(100)) was the highest, and the energy barrier of first hydrogenation step was 0.342 eV. More importantly, Ir@Fe(100) can significantly inhibit the hydrogen evolution reaction. This study can provide some theoretical reference and guidance for the design and preparation of Fe-based catalysts.

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview.

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH3 ) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH3 . The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N2 adsorption and activation by donating p electrons. In this work,wesystematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.

Electrochemical nitrogen reduction reaction over gallium - a computational and experimental study.

Ga was identified earlier as one of the "overlooked" metals for catalyzing the electrochemical nitrogen reduction reaction (ENRR). We investigate here the electrocatalytic activity of Ga towards the nitrogen reduction reaction. We used a combination of molecular modelling and simulations using periodic density functional theory calculations (DFT), and experimental ENRR measurements. The ENRR was found to proceed via an associative mechanism where the first PCET to dinitrogen forming the surface adsorbed N2H* species is the overpotential limiting step. The bare Ga cathode has a high overpotential (>2 V (SHE)) for the ENRR. We also investigated the effect of a water-in-salt electrolyte (WISE) on the rate of ammonia formation. The addition of an Li salt lowers the overpotential to 1.88 V (SHE). DFT calculations revealed that the H-adatom was more favorably bound than the N-adatom, and the hydrogen evolution reaction (HER) is expected to dominate at high cathodic potentials. Experimental ENRR tests corroborate our results wherein no significant NH3 formation was detected. The low electrochemical activity of Ga is attributed to poor binding and activation of N2 which originates from an electropositive surface charge distribution.

Reactivity of nitrogen atoms from Zif-8 structure deposited over Ti3C2 MXene in the electrochemical nitrogen reduction reaction.

The electrochemical nitrogen reduction reaction (NRR) to produce NH3 is the most efficient, eco-friendly and cost-effective alternative to the Haber-Bosch process. It is crucial to investigate and develop electrocatalysts selective for NH3 synthesis. In recent studies, the Ti3C2 MXene has emerged as a highly promising electrocatalyst for the NRR process. In this work, we explore the effect of Zif-8 addition over MXene sheets in order to control the rate of hydrogen evolution reaction (HER). Despite the better result obtained for Zif-8@Ti3C2 (3.0 μg NH3 gcat-1 h-1 at -0.55 V/RHE), the ammonia produced when using Zif-8@Ti3C2 as cathode material is shown to be originated from nitrogen atoms contained in the Zif-8 structure instead of those of N2. The results shed light to the need to fully understand the N2 electroreduction process over N-containing electrocatalysts.

High-throughput design of bimetallic core–shell catalysts for the electrochemical nitrogen reduction reaction

Design strategies for core–shell or multilayered electrochemical NRR catalysts are suggested based on high-throughput DFT calculations of transition-metal core–shell catalysts.

Engineering hydrophobic-aerophilic interfaces to boost N2 diffusion and reduction through functionalization of fluorine in second coordination spheres.

Ammonia is a crucial biochemical raw material for nitrogen containing fertilizers and a hydrogen energy carrier obtained from renewable energy sources. Electrocatalytic ammonia synthesis is a renewable and less-energy intensive way as compared to the conventional Haber-Bosch process. The electrochemical nitrogen reduction reaction (eNRR) is sluggish, primarily due to the deceleration by slow N2 diffusion, giving rise to competitive hydrogen evolution reaction (HER). Herein, we have engineered a catalyst to have hydrophobic and aerophilic nature via fluorinated copper phthalocyanine (F-CuPc) grafted with graphene to form a hybrid electrocatalyst, F-CuPc-G. The chemically functionalized fluorine moieties are present in the second coordination sphere, where it forms a three-phase interface. The hydrophobic layer of the catalyst fosters the diffusion of N2 molecules and the aerophilic characteristic helps N2 adsorption, which can effectively suppress the HER. The active metal center is present in the primary sphere available for the NRR with a viable amount of H+ to achieve a substantially high faradaic efficiency (FE) of 49.3% at -0.3 V vs. RHE. DFT calculations were performed to find out the rate determining step and to explore the full energy pathway. A DFT study indicates that the NRR process follows an alternating pathway, which was further supported by an in situ FTIR study by isolating the intermediates. This work provides insights into designing a catalyst with hydrophobic moieties in the second coordination sphere together with the aerophilic nature of the catalyst that helps to improve the overall FE of the NRR by eliminating the HER.

One-step synthesized Nb2O5−y-decorated spinel-type (Ni,V,Mn)3O4−x nanoflowers for boosting electrocatalytic reduction of nitrogen into ammonia

Two renewable methods for reducing greenhouse gas emissions associated with ammonia (NH3) production are the renewable H2-combined Haber–Bosch process and the electrochemical nitrogen reduction reaction (eNRR).

Electrochemical ammonia synthesis under ambient conditions using TM-embedded porphine-fused sheets as single-atom catalysts.

In this research, we systematically investigated the reaction mechanism and electrocatalytic properties of transition metal anchored two-dimensional (2D) porphine-fused sheets (TM-Por) as novel single-atom catalysts (SACs) for the electrochemical nitrogen reduction reaction (eNRR) under ambient conditions. Using high-throughput screening and first-principles calculations based on the density functional theory (DFT) method, three eNRR catalyst candidates, i.e. Mo-Por, Tc-Por, and Nb-Por, were screened out, with the eNRR onset potentials on them being -0.36, -0.53, and -0.74 V, respectively. Furthermore, these catalyst candidates all have good stability and selectivity. Analyzing the band structures found that these catalyst candidates all are metallic, which is needed for good electrocatalysts. Ab initio molecular dynamics (AIMD) simulations show that these catalyst candidates have good stability at 500 K. It is hoped that our work will open up new possibilities for the experimental synthesis of electrochemical ammonia catalysts.

Paradigm in single-atom electrocatalysts for dinitrogen reduction to ammonia

Single-atom catalysts (SACs) are a new class of electrocatalysts for the electrochemical nitrogen reduction reaction.

MIL-101(Fe)@Nb2C MXene for efficient electrocatalytic ammonia production: an experimental and theoretical study

The environment-friendly electrochemical nitrogen reduction reaction (NRR) is considered to be a promising alternative to the traditional Haber–Bosch process for ammonia production.