High-efficiency ammonia electrosynthesis on self-supported Co2AlO4 nanoarray in neutral media by selective reduction of nitrate

A Co2AlO4 nanosheet array on carbon cloth (Co2AlO4/CC) is proposed as a superb electrocatalyst for converting nitrate (NO3−) to ammonia (NH3). In 0.1 M PBS solution with 0.1 M NO3−, it attains an NH3 yield of 7.9 mg h−1 cm−2 with a Faradaic efficiency of 92.6%, with high durability. A Zn-NO3− battery with such Co2AlO4/CC as cathode offers a power density of 3.43 mW cm−2 with an NH3 yield of 750 μg h−1 cm−2. Theoretical calculations reveal that Al ions reduce the electron cloud density on the surface of Co, making it highly conducive to NO3− adsorption at Co sites. Additionally, Co2AlO4 (2 2 0) surface inhibits hydrogen evolution reaction but is highly active for NO3− reduction with a low energetically uphill pathway (ΔG of 0.42 eV) for the potential-determining step (*NO3 to *NO3H), much smaller than that of Co3O4 (2 2 0) (ΔG of 0.83 eV).