A CoOxHy/β-NiOOH electrocatalyst for robust ammonia oxidation to nitrite and nitrate

As the global demand for fertilisers and other nitrogenous products increases, so does the demand for robust, cost-effective and sustainable alternatives to the Ostwald process for the oxidation of ammonia to NOx compounds. Attention has turned to the electrochemical ammonia oxidation to nitrite and nitrate ([NO2/3]−) – a process that could enable distributed production of these important commodity chemicals. Studies of the ammonia oxidation reaction (AOR) for the synthesis of [NO2/3]− are now trending towards more selective and cheaper catalytic materials, rather than the optimisation of Pt and other known noble metal-based catalysts that are subject to poisoning and/or corrosion. Towards this goal, we describe a composite of CoOxHy and β-NiOOH on a Ni foam substrate as an electrocatalyst for the AOR that enables generation of [NO2/3]− under alkaline conditions over extended periods of operation. Specifically, the average [NO2/3]− yield rate of 1.5 ± 0.5 nmol s−1 cm−2 with a faradaic efficiency of 79% ± 10% is demonstrated over 4 days of continuous operation. These results represent a step forward in the development of more robust, corrosion-resistant, and industrially practical materials for the sustainable production of nitrates and nitrites.