Cobalt oxide micro flowers derived from hydrothermal synthesised cobalt sulphide pre-catalyst for enhanced water oxidation

The rational design and development of the low-cost and efficient electrocatalysts towards oxygen evolution reaction (OER) are greatly influenced by the exposed surface area and structure of the electrocatalyst. Herein, we show a flower-like cobalt oxide/cobalt sulphide nanosheet electrocatalyst via a simple and cheap one-step hydrothermal synthesis for electrochemical water oxidation. Tuning the sulphur concentration influences the crystal formation and structural direction to achieve flower-like morphologies that greatly improves the surface area to benefit the OER. The best OER electrocatalysts were achieved on the CoS (1:0.5) electrode, which can deliver a current density of 10 mA cm−2 at a small overpotential of 383 mV, a low Tafel slope (38 mV dec−1) and remains constant for over 24 h. Mechanism study shows that during OER, the cobalt sulphide acts as a pre-catalyst and produces more active cobalt oxide phases with higher Co valence state when undergoing oxidation. This innovative design demonstrates the catalytic activity and overall efficiency which can be applied as an efficient non-noble metal electrocatalyst for OER.