Enhanced oxygen evolution reaction in hierarchical NiFe/NiO electrocatalysts: Effects of electrodeposition condition on electrode

This study fabricated an OER electrocatalyst with a hierarchical structure by electrodepositing Ni-Fe on NiO. The prepared electrocatalyst exhibited high activity and stability. Furthermore, the OER characteristics of the NiFe/ NiO electrode were investigated by changing the metal (Ni and Fe) concentration and Ni:Fe ratio in the plating bath. As the plating bath concentration decreased, NiFe-layered double hydroxide was prominently formed due to an increase in local pH. The electrode obtained using a relatively low plating bath concentration of 130 mM demonstrated high activity with an overpotential of 245 mV and Tafel slope of 27.6 mV dec(-1) at a current density of 10 mA/cm(2). When the Ni:Fe ratio in the plating bath was adjusted, OER activity increased as the Fe content of the electrode increased to approximately 20.9 at.%, and as the Fe content increased beyond that, the activity gradually decreased. Fe inhibits Ni oxidation and acts as an active site owing to Fe3+ substitution in the gamma-NiOOH structure, resulting in increased OER activity. However, when the Fe content was > 29 at.%, the inactive phase gamma-FeOOH predominantly grew and the OER activity decreased.