Accelerating N2H4(ads) formation by frustrated Lewis pairs in oxyhydroxide for electrocatalytic ammonia oxidation into N2

Abstract

Conventional catalysts based on individual Oswin and Salomon (O-S) or Gerischer and Mauerer (G-M) mechanism cannot achieve direct electrocatalytic ammonia (NH3) oxidation into nitrogen (N2) with high activity and selectivity. Herein, a bimetallic nickel-cobalt oxyhydroxide (Ni0.5-Co0.5-OOH) with frustrated Lewis pairs was developed through an elaborate analysis of the binding types of NH3 with metal-oxide anode, efficiently integrating O-S and G-M mechanisms for converting NH3 into N2 with high activity (94%) and selectivity (63%), which is much superior to the anodes in the previous reports. The evidence of batch experiments, in-situ characterizations, and theoretical calculations confirms that two NH3 molecules bind to Co3+ sites (Lewis acid) in CoOOH and hydroxy sites (Lewis base) in NiOOH, respectively. Then, the NH2(ads) generated on the Lewis acid sites can quickly recombine with the NH2(ads) desorbed from the Lewis base sites, accelerating the formation of N2H4(ads) and preventing the peroxidation of NH3. The electrocatalytic system assembled with Ni0.5-Co0.5-OOH anode shows excellent performance for NH3 elimination in secondary aerobic process effluent. Our work provides precious guidance for the design of novel anodes and sheds light on further promoting the performance of ammonia conversion.