Unraveling the formation of optimum point in NiCo-based electrocatalysts for urea oxidation reaction

The urea oxidation reaction (UOR) has been recognized as a potential replacement for the hydrogen oxidation reaction in anion exchange membrane fuel cells, as well as the oxygen evolution reaction in water electrolyzers. For the successful application of this technology, advanced electrocatalysts for UOR must be developed to overcome the high overpotential. This can be achieved by introducing Co into Ni-based catalysts. Normally, an optimum ratio of Ni:Co would show the highest activity; however, a higher content of Co adversely affects the catalyst performance. In this study, we provide an explanation for the optimum point in NiCo-based catalysts. In addition to the positive effect of reducing the UOR onset potential, electrochemical analyses suggested that an electro-inactive species for UOR was formed by doping with Co, and this species exerted its influence more strongly as the content of Co increased. Thus, the performance was maximized at an optimum ratio of Ni:Co, at which the advantages and disadvantages of Co-doping were balanced. The results of our study indicated that Co-doping at 10 at% showed the highest UOR catalytic activity as proven by the electrochemical measurements.