Modulation of the Lattice Structure of CuFe/Copper Foam Catalysts by Doping with Bi to Improve the Efficiency of Electrocatalytic Ammonia Synthesis

Nitrogen reduction reaction (NRR) offers a sustainable alternative to the energy-intensive Haber-Bosch process for ammonia synthesis under ambient conditions while also mitigating the serious global warming impact of fossil fuels. However, the competing hydrogen evolution reaction remains a significant challenge in NRR systems. In this work, we propose Bi-doped CuFe nanoclusters loaded on 3D copper foams (CFs) as an enhanced N₂ electrocatalyst for NRR. The Bi-doped catalyst exhibited superior NRR activity compared to the undoped counterpart, achieving a high ammonia yield of 216.1 μg h^-1 cm^-2 with a Faradaic efficiency of 46.8% at −0.4 V vs reversible hydrogen electrode. Importantly, the catalyst also showed good selectivity with minimal N₂H₄ byproduct generation and excellent stability. Bismuth incorporation induced lattice expansion and electronic defects, which in turn created structural defects and oxygen vacancies. These changes effectively promoted the adsorption and activation of N₂ molecules. Comprehensive characterization revealed that Bi doping decreased the oxygen vacancy density in the bulk phase but increased the density on the surface. This phenomenon expanded the lattice spacing, inhibiting H* combination to produce H₂, while the surface oxygen vacancies regulated the adsorption strength of N₂ and N_xH_y intermediates during the electrocatalytic process. Density functional theory calculations further confirmed that Bi doping enhanced N₂ adsorption and activation on the active sites, as well as the subsequent hydrogenation steps, leading to a lower energy barrier for the distal pathway to NH₃ formation. Moreover, the Zn-N₂ battery assembled with Bi-CuFe/CF shows an excellent power density of 14.01 mW cm^-2, which enables simultaneous ammonia production and energy supply, which gives it significant potential in the field of sustainable energy. This work demonstrates a promising approach to developing efficient ammonia synthesis electrocatalysts by lattice structure modulation, contributing to the transition toward a low-carbon economy.