Metal nitride nanosheets enable highly efficient electrochemical oxidation of ammonia

Ammonia has been recognized as a promising hydrogen mediator as it reduces the expense of the long-range transportation of hydrogen. However, methods to extract hydrogen from ammonia require improvements to decrease the overall cost. Ammonia electrolysis provides a convenient method to attain a low-cost hydrogen production. Here, we report that nickel-cobalt nitride nanosheets can achieve high electrocatalytic activity for the ammonia oxidation reaction (AOR) in non-aqueous solutions. The AOR onset overpotential of NiCo2N nanosheets is 0.55 V, which is about 0.25 V lower than that of the Pt/C electrocatalyst. Our ultraviolet–visible and mass spectroscopy studies reveal that NiCo2N nanosheets bypass the formation of the soluble metal-amine complex and preferentially oxidize ammonia to environmentally friendly diatomic nitrogen with a Faradic efficiency of over 90%. Theoretical simulation further indicates that the downshift of metal d-band on NiCo2N nanosheets surface helps retain a long-lasting electrocatalytic activity. Overall, this work introduces a new family of active and stable electrocatalysts for AOR that is based on earth-abundant transition metals, heralding the feasibility of using ammonia as a hydrogen mediator in hydrogen-based applications.