Modulating the coadsoption of hydroxyl and nitrogenous groups induced by Ni and Cu doping on FeOOH for accelerating dehydrogenation in the ammonia oxidation reaction

Owing to its high hydrogen content and carbonfree nature, ammonia is a promising energy carrier used in powering fuel cells and an alternative oxidation substrate to water in electrolytic hydrogen production devices. However, the insufficient mechanistic understanding and the lack of inexpensive and efficient catalysts for the ammonia electrooxidation reaction (AOR) have hampered the development of the ammonia-based energy system. In this work, novel Ni and Cu co-doped porous FeOOH nanorods (NiCu-FeOOH) synthesized by a light-induced chemical precipitation method can serve as the AOR catalyst with efficient catalytic activity (1.41 V at an anodic current density of 10 mA cm(-2)) and enhanced stability in an aqueous ammonia solution. According to the experimental data and theoretical calculation results, the synergistic effect of heterogeneous Ni and Cu atoms makes Ni and Fe sites on the surface of NiCu-FeOOH exhibit a suitable electronic structure to coadsorb nitrogenous intermediates and hydroxyl groups at the top of the volcano plot and thereby accelerate dehydrogenation in the AOR. The backward shift of the rate-determining step (RDS) ((NH2)-N-star + (OH)-O-star formation step shifts to (N2H3)-N-star + (OH)-O-star formation step) and the lower energy barrier of the RDS (0.86 eV) reveal that the Ni and Cu co-doping makes FeOOH crystals active for the AOR. The coadsorption reaction pathway involved in nitrogenous intermediates and hydroxyl groups has been innovatively proposed to effectively describe and simulate the AOR process, which opens a new horizon to design low-cost and stable AOR catalysts.

Automated summary

This study synthesized Ni and Cu co-doped porous FeOOH nanorods (NiCu-FeOOH) using a light-induced chemical precipitation method as a catalyst for the ammonia electrooxidation reaction (AOR). The NiCu-FeOOH showed efficient catalytic activity and enhanced stability in an aqueous ammonia solution. The synergistic effect of Ni and Cu atoms on the surface of NiCu-FeOOH promoted the coadsorption of nitrogenous intermediates and hydroxyl groups, accelerating the AOR dehydrogenation reaction.