Scalable and energy-efficient synthesis of CoxP for overall water splitting in alkaline media by high energy ball milling

Abstract

Earth-abundant catalysts based on transition metal phosphides (TMPs) such as Co_xP have recently gained a lot of attention in the field of electrocatalysis and are usually acquired by chemical synthesis. Herein, we present a mechanical synthesis method (high energy ball milling) for preparing a bifunctional Co_xP electrocatalyst at room temperature (25 °C) using black phosphorus (BP) and cobalt(III) oxide (Co₂O₃) as raw materials. This safe, energy-efficient and scalable method yields a durable catalyst material, which achieves a current density of 10 mA cm⁻² at low overpotentials of 69 mV and 266 mV in 1 M KOH for the HER and OER, respectively, as well as low Tafel-slopes of 50.6 mV dec⁻¹ and 62.1 mV dec⁻¹. When the Co_xP electrocatalyst was employed for overall water splitting, current densities of 10 mA cm⁻² and 100 mA cm⁻² were achieved at 1.59 V and 1.97 V surpassing those of the state-of-the-art Pt/C‖RuO₂ setup. Moreover, the outlined synthesis route could potentially be applied to other transition metals allowing for the facile production of other catalysts.