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

Abstract

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 NO_x compounds. Attention has turned to the electrochemical ammonia oxidation to nitrite and nitrate ([NO_2/3]⁻) – a process that could enable distributed production of these important commodity chemicals. Studies of the ammonia oxidation reaction (AOR) for the synthesis of [NO_2/3]⁻ 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 CoO_xH_y and β-NiOOH on a Ni foam substrate as an electrocatalyst for the AOR that enables generation of [NO_2/3]⁻ under alkaline conditions over extended periods of operation. Specifically, the average [NO_2/3]⁻ 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.