Comparison of the effects of cation and phosphorus doping in cobalt-based spinel oxides towards the oxygen evolution reaction

The sluggish kinetics of the oxygen evolution reaction (OER) has become a hindrance for the development of clean and sustainable energy technology and calls for highly efficient electrocatalysts. Recently, heteroatom doping has exhibited good prospects to boost the electrocatalytic performance of materials. Herein, we selected the typical MCo₂O₄(M = transition metal)-type spinel oxides to test the doping effects aroused by metal cations and non-metal phosphorus (P) towards the OER in alkaline media. Not surprisingly, both cation and P dopants improved the OER activity. Additionally, P doping gave a further decrease of overpotential (reduced 34-194 mV) and Tafel slope (reduced 9.59-207.55 mV dec⁻¹) compared to the oxide counterparts. Specifically, P-doped (Zn_0.33Ni_0.33Mn_0.33)Co₂O₄showed the best OER performance with the lowest overpotential of 0.349 V at 10 mA cm⁻²and Tafel slope of 69.68 mV dec⁻¹and good stability after 2000 cycles of cyclic voltammetry. Redox pairs, oxygen vacancies, crystallinity and electrochemical active surface area were greatly modulated by heteroatom doping and together influenced the OER performance. This work confirms the synergistic effect of both metal and non-metal doping and the larger contribution of P dopants towards the OER, which gives a hint to develop superior electrocatalysts.