Comparison of the Catalytic Properties of Pt and Co Cathodes for the Nitrite Reduction Reaction to Ammonia

Abstract

The authors study the electrochemical reduction of nitrites (NO\(_{2}^{ - }\)RR) in a neutral aqueous electrolyte. This reduction reaction has important applications both for future ammonia synthesis processes for effective treatment of industrial and agricultural wastewaters. Catalytic activity is compared (results on the Faradaic efficiency and yield rate of ammonia are presented) for noble (platinum) and non-noble (cobalt) metals. Metallic polycrystalline platinum and cobalt serve as electrocatalysts. The surfaces of the catalysts are analyzed via SEM and optical microscopy. Linear voltammetry is used to preliminarily identify the potential of ammonia synthesis and estimate the current density of synthesis. The Faradaic efficiency (FE) and yield rate of ammonia release are obtained for five selected values of current densities (J). It is found that a cobalt cathode is most efficient (FE ≈ 99%, yield rate (NH₃) = 2.4 mmol h⁻¹ cm⁻²), which exceeds the values for the platinum cathode (FE = 88.1%, yield rate (NH₃) = 0.4 mmol h⁻¹ cm⁻²). The electrochemically active surfaces (ECSAs) of the electrocatalysts are determined. This activity of catalysts is explained according to results in this work, and shows that a non-noble metal cathode can be more effective for NO\(_{2}^{ - }\)RR.