Accelerating N₂H_4(ads) formation by frustrated Lewis pairs in an oxyhydroxide for electrocatalytic ammonia oxidation...

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.