Oxygen‐Containing Anions Promote the Electrocatalytic Activity of Ni(OH)2/NiOOH for The Urea Oxidation

Abstract

AbstractThe electrocatalytic oxidation of urea (EOU) is an important half‐reaction in water splitting, urea fuel cells, and urea wastewater treatment. The anions of nickel‐based catalysts can be leached severely in the oxidation potential range. Therefore, the influence of anion on the electrocatalytic performance of Ni(OH)2/NiOOH for urea oxidation has not been systematically studied. The present experimental results show that the structure reconstruction of catalyst is a complicated process, specifically including deep penetration by alkaline electrolyte, leaching‐induced oxidation by phosphorus or sulfur anions, transformation or cracking of the original structure, and formation of an amorphous layer on the surface. The reconstructed NF‐NiPx‐R or NF‐NiSx‐R has a three‐layer core‐shell structure, with a nickel foam skeleton in the innermost layer, an amorphous NiPx or NiSx layer in the middle layer, the outermost layer of oxygen‐containing anion (POx or SOx) coordinated Ni(OH)2. In the prepared catalyst, the Ni(OH)2/NiOOH redox is the real catalytic species for the urea oxidation. It is found that the oxygen‐containing anion can enhance the catalytic performance of the Ni(OH)2/NiOOH redox, and POx anion has the best enhancing effect. It is found that the urea molecules are oxidized on the electrocatalyst surface mainly through an indirect pathway.