Facet-engineered Fe- and Co-decorated Cu2O (111) for highly efficient concurrent electrocatalytic ammonia synthesis and methanol oxidation

Abstract

Ammonia (NH₃) plays an important role in modern industry and agriculture. The electrocatalytic nitrogen reduction reaction (NRR) establishes a greener and more energy-efficient pathway compared to the traditional Haber–Bosch process. However, the intrinsic correlation mechanism between the high ammonia yield of the catalyst and NRR kinetics has not yet been fully elucidated. In this work, we developed a new crystal facet engineering strategy involving Fe and Co doping on Cu₂O with exposed (111) facets to enhance the catalyst's ammonia synthesis rate, achieving a high ammonia yield of 140 μg h⁻¹ cm⁻² with a faradaic efficiency (FE) of 23% at −0.5 V vs. RHE. Through in situ Raman experiments and DFT calculations, the high catalytic performance of FeCo–Cu₂O (111) is attributed to the well-matched and optimized tandem catalysis of N₂ hydrogenation steps and NH₃ desorption, whereby Fe/Co dopants promote the conversion of N₂ into *NNH (the rate-determining step, RDS), while the exposed Cu₂O (111) plane facilitates NH₃ desorption and enhances electron transfer during the NRR process. Furthermore, in order to explore its potential for industrial applications, FeCo–Cu₂O (111) was used as the cathode in a Zn–N₂ battery, delivering a power density of 14.17 mW cm⁻² and exhibiting excellent cycling stability, which enables simultaneous ammonia production and energy supply. Notably, when paired with methanol oxidation at the anode, the system enables concurrent production of green ammonia and value-added products. The overall cell voltage required for the NRR is decreased by 111 and 216 mV at 50 mA cm⁻², compared to NRR/OER co-electrolysis and HER/OER co-electrolysis, respectively, which significantly reduces the overall energy consumption for ammonia synthesis. This integrated approach presents a sustainable pathway for coupling energy conversion with chemical synthesis. This work introduces an effective methodology for enhancing the selectivity and activity of electrocatalytic nitrogen reduction through crystal facet and dopant engineering, which plays a pivotal role in tackling the energy crisis and driving the shift towards a low-carbon economy.