Influence of cobalt dopant in NiFe2-xCoxO4 (0≤x≤2) on electrochemical catalytic properties

Environmental pollution has increased owing to the excessive consumption of fossil fuels. Thus, the combustion of which does not emit pollutants, has attracted attention for as an alternative fuel in various energy application systems. Using hydrogen energy has considered as an environmentally friendly solution to significantly reduce the dependency on fossil fuels and it can be produced by electrochemical water splitting. However, the sluggish kinetic reaction of the oxygen evolution reaction (OER) during electrochemical water splitting reduces the efficiency of hydrogen energy. Therefore, an excellent electrochemical catalyst with superior electrochemical activity in OER is required to increase the energy conversion efficiency. In this study, a NiFe_2-xCo_xO₄ (0 ≤ x ≤ 2) electrochemical catalyst was prepared by hydrothermal synthesis by controlling the amount of Co dopant. The influence of Co doping on the electrochemical catalytic activity of the prepared sample was evaluated by comparing the oxygen vacancies, bandgap, macroporosity and active surface area. Previous research have reported that abundant oxygen vacancies can improve the electrochemical catalytic activity. However, NiCo₂O₄ with the least number of oxygen vacancies exhibited excellent bifunctional catalytic activity for OER/oxygen reduction reaction (ORR) owing to the development of macropore, large active surface areas, and lower bandgap. Therefore, the bandgap and porosity such as macroporosity, large surface area, are an important factor that exert a greater influence than oxygen vacancies in electrochemical catalysts.