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The electrocatalyzed ammonia oxidation reaction (AOR) is a potential pathway toward waste ammonia remediation, energy generation, and the synthesis of value‐added products. To date, mechanistic studies have focused on elucidating the progress of AOR on Pt‐based catalysts with an established pathway for N2$\mathrm{N_2}$ only. In this work, density functional theory was applied to determine the lowest energy intermediates toward nitrogen gas, nitrite, and nitrate formation on β$\beta$‐Ni(OH)2$\mathrm{Ni(OH)_2}$, a promising electrocatalyst material for AOR. It was found that dinitrogen formation progresses via NH‐NH coupling, whereas nitrite and nitrate formation occurs via deprotonation of ammonia to form adsorbed N and subsequent hydroxylation to form oxygenated intermediates. This work is the first to report a mechanism for nitrite and nitrate formation and will also serve as a benchmark for future studies on Ni‐based materials. [ABSTRACT FROM AUTHOR]

We discuss the environmental and energetic benefits of coupling nitrogenous waste treatment with the electrochemical conversion of CO2 to value-added products via direct reduction or electrocarboxylation. In particular, we demonstrate that co-electrolysis of urea or ammonia with CO2 requires significantly lower cell voltages than CO2 electrolyzers relying on the oxygen evolution reaction as an anodic process. [ABSTRACT FROM AUTHOR]

The electrochemical urea oxidation reaction (UOR) to N 2 represents an efficient route to simultaneous nitrogen removal from N-enriched waste and production of renewable fuels at the cathode. However, the overoxidation of urea to NO x - usually dominates over its oxidation to N 2 at Ni(OH) 2 -based anodes. Furthermore, detailed reaction mechanisms of UOR remain unclear, hindering the rational catalyst design. We found that UOR to NO x - on Ni(OH) 2 is accompanied by the formation of near stoichiometric amount of cyanate (NCO - ), which enabled the elucidation of UOR mechanisms. Based on our experimental and computational findings, we show that the formation of NO x - and N 2 follows two distinct vacancy-dependent pathways. We also demonstrate that the reaction selectivity can be steered towards N 2 formation by altering the composition of the catalyst, e.g., doping the catalyst with copper (Ni 0.8 Cu 0.2 (OH) 2 ) increases the faradaic efficiency of N 2 from 30 % to 55 %., (© 2022 Wiley-VCH GmbH.)