Waxberry-like hydrophilic Co-doped ZnFe₂O₄ as bifunctional electrocatalysts for water splitting

Water splitting is a promising technique for clean hydrogen production. To improve the sluggish hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the development of efficient bifunctional electrocatalysts for both HER and OER is urgent to approach the scale-up applications of water splitting. Nowadays transition metal oxides (TMOs) are considered as the promising electrocatalysts due to their low cost, structural flexibility and stability, however, their electrocatalytic activities are eager to be improved. Here, we synthesized waxberry-like hydrophilic Co-doped ZnFe₂O₄ electrocatalysts as bifunctional electrocatalysts for water splitting. Due to the enhanced active sites by electronic structure tuning and modified super-hydrophilic characteristics, the spinel ZFO-Co_0.5 electrocatalyst exhibits excellent catalytic activities for both OER and HER. It exhibits a remarkable low OER overpotential of 220 mV at a current density of 10 mA cm^-2 and a Tafel slope of 28.2 mV dec^-1. Meanwhile, it achieves a low overpotential of 73 mV at a current density of 10 mA cm^-2 with the Tafel slope of 87 mV dec^-1 for HER. In addition, for water electrolysis device, the electrocatalytic performance of ZFO-Co_0.5||ZFO-Co_0.5 surpasses that of commercial IrO₂||Pt/C. Our work reveals that the hydrophilic morphology regulation combined with metallic doping strategy is a facile and effective approach to synthesize spinel TMOs as excellent bifunctional electrocatalyst for water splitting.