Improving Electrocatalytic Nitrogen Reduction Selectivity and Yield by Suppressing Hydrogen Evolution Reaction via Electronic Metal–Support Interaction

Abstract

the H 2 precursor. This energy-intensive process reportedly costs ≈1.5% of the annual global energy consumption. [1,2] The electrocatalytic N 2 reduction reaction (NRR), which uses a renewable energy source and N 2 and H 2 O as the reactants, presents a highly promising strategy for NH 3 production under ambient conditions. [3][4][5][6][7] However, two aspects: poor catalytic activity and low selectivity of the electrocatalyst, significantly restrict the NRR process. First, the inert nitrogen with high cleavage energy (940.95 kJ mol −1 ) has sluggish adsorption on the catalysts, owing to the lack of active sites on the catalyst to accept N 2 lone-pair electrons. [8,9] Second, the potentials needed to proceed with the electrochemical NRR are usually similar to that required for the hydrogen evolution reaction (HER). [10,11] During the conversion from N 2 to NH 3 , the attendant HER competes for the consumption of electrons reducing the Faraday efficiency. Therefore, it is highly desirable but still remains a challenge to design an electrocatalytic system that could efficiently and selectively electroreduction of N 2 to NH 3 .The general electrocatalytic NRR process involves the adsorption of N 2 on active sites and the subsequent combination of protons (and electrons for the hydrogenation of the bound N 2 . [12,13] To achieve these multiple H-coupled electrontransfer steps, various kinds of heterogeneous electrocatalysts have been examined for NRR, such as transition metals, metal oxides, nitrides, sulfides, carbides, and borides. [14][15][16][17][18][19] A few heterogeneous transition metal based catalysts have been proven effective for increasing the N 2 adsorption and alleviating the reaction barriers. However, since general metal catalysts are inherently more inclined to adsorb H, most active sites and electrons are occupied and consumed by unwanted hydrogen atoms, leading to a domination of the competing HER over the NRR and the impediment of the NRR catalytic activity and selectivity. [20,21] To improve the NRR selectivity, various methods like limiting the accessibility of H and electrons, changing the chemical equilibrium of the HER, and designing catalysts to reduce the HER activity have been employed to suppress the HER. [20][21][22][23][24][25][26][27] Among them, studies focusing on the investigation of supports for a stronger adsorption of N 2 than H to inhibit the HER and improve the overall conversion of N 2 to NH 3The electrochemical nitrogen reduction reaction (NRR) has the potential to replace the Haber-Bosch process for ammonia synthesis under ambient conditions. However, the selectivity and yield of the NRR are impractical, owing to the preferential binding of the electrocatalyst to H and the consequential coverage of active sites. In this study, VO 2 , with N 2 strongly adsorbed over H atoms, is used as a support to provide a N 2 source to avoid the hydrogen evolution reaction. Mo, with a high NRR activity, is introduced as the active site to promote the NRR. Meanwhile, the electronic metal-su...

NH3 Electrosynthesis from N2 Molecules: Progresses, Challenges, and Future Perspectives

“…At present, the development of NRR is still in its infancy stage and has encountered with several bottleneck issues. The FE (<60%), NH 3 partial current density ( j NH3 , < 1 mA cm –2 ), and NH 3 yield rate (at the level of 10 –9 mol s –1 cm –2 ) of NRR remain relatively low mainly due to the lack of efficient electrocatalysts. ,, Accordingly, developing efficient electrocatalysts and building the structure–activity relationship that can guide the design and optimization of electrocatalysts still should be the primarily tasks for the field. To achieve the goals, the advanced in situ spectroscopic techniques ( e.g.…”

Ambient Electrochemical Ammonia Synthesis: From Theoretical Guidance to Catalyst Design

“…The effect of electronic metal‐support interaction between metal Mo and VO 2 on NRR performance was evaluated (Figure 6c ), in which the electron‐defect‐rich Mo induced via electronic metal‐support interaction can effectively destabilize * N 2 and lower the energy barrier of the subsequent hydrogenation process. [ 85 ] Compared with VO 2 , the enhanced yield rate (10.8 times) and Faradic efficiency (2.8 times) were obtained by the addition of Mo. The ∆ G ( * N 2 ) − ∆ G ( * H) was chosen as the descriptor of NRR selectivity shown in Figure 6d,e , [ 86 ] where RuCu with more negative value (∆ G ( * N 2 ) − ∆ G ( * H)) achieved a higher Faradic efficiency compared with that of Ru.…”

“…Reproduced with permission. [ 85 ] Copyright 2023, Wiley VCH. d) Schematic illustration of the synthesis of Ru–Cu nanoparticles.…”

Metal-Based Electrocatalysts for Selective Electrochemical Nitrogen Reduction to Ammonia

“…However, apart from the difficulty of nitrogen activation, the e-NRR in aqueous solution is limited by the competition of HER [ 42 ]. Several processes at the electrode–electrolyte interface occur concurrently, involving the diffusion and adsorption of reactant species, transfer of electrons and protons, as well as desorption of species, where e-NRR and HER share some reaction species for basically electro-hydrogenation reactions [ 43 , 44 ].…”