Electrochemical construction of S-doped MnOx/Mn integrated film on carbon paper in a choline chloride based deep eutectic solvent for enhanced electrochemical water oxidation

Abstract

The rational design and synthesis of highly efficient, precious metal-free electrocatalysts in the promotion of electrochemical water oxidation is essential for the sustainable use of renewable energy. Herein, an integrated, S-doped MnOx/Mn film developed on carbon paper (CP) formed by a two-step transformation approach that includes template-free electrodeposition and in-situ electrochemical oxidation is employed as an efficient oxygen evolution reaction (OER) electrocatalyst. The doping of S and in-situ electro-oxidation lead to a tailored electronic structure and phase composition, which endow the composite electrode with a significantly enhanced OER catalytic performance. This S-doped integrated electrode perfectly combines highly active MnOx outer layers with conductive metallic Mn inner layers to offer abundant catalytic interfaces and electronic paths, leading to favorable reaction kinetics. As a result, the optimal S-doped MnOx/Mn/CP offers a low overpotential of 435 mV at 10 mA cm−2 with a Tafel slope of 89.97 mV dec−1 as well as improved stability. Impressively, a highly intrinsic catalytic activity with a turnover frequency of 0.0112 s−1 is obtained for S-doped MnOx/Mn/CP, which is 4.2-fold higher than that of MnOx/Mn/CP. S doping plays a critical role in stabilizing the MnIIIOx active phase and is ultimately responsible for the enhanced catalytic performance. This work provides an integrated design concept and S doping approach suitable for boosting the OER catalytic performance of MnOx.