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

Abstract

Conventional catalysts based on the 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 (Ni_0.5–Co_0.5-OOH) with frustrated Lewis pairs was developed through an elaborate analysis of the binding types of NH₃ with the 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 characterization, 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 NH_2(ads) generated on the Lewis acid sites can quickly recombine with the NH_2(ads) desorbed from the Lewis base sites, accelerating the formation of N₂H_4(ads) and preventing the peroxidation of NH₃. The electrocatalytic system assembled with the Ni_0.5–Co_0.5-OOH anode shows excellent performance for NH₃ elimination in the 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.