Sulfur-doped cobalt molybdenum oxide with a hydrangea-like structure for bi-functionally efficient overall water splitting

Abstract

Developing an efficient bi-functional water-splitting catalyst is crucial for advancing sustainable hydrogen energy applications. A novel sulfur-doped cobalt molybdenum oxide (CoMoO) catalyst with a hydrangea-like structure was synthesized in situ on a carbon fiber paper substrate using a simple one-step hydrothermal process. The optimized sample exhibits excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity with an overpotential of 105 and 205 mV at a current density of 10 mA cm⁻² under alkaline conditions, respectively. Experimental characterization shows that the introduction of sulfur efficiently modifies the composition and morphology of the CoMoO electrocatalyst, which increases the electrochemically active surface area and improves the electrocatalytic kinetics. The improved electrocatalytic performance can be attributed to the synergistic effects of the various metal ion constituents. Mo⁴⁺ enhances water adsorption and accelerates the reaction kinetics of H₂ generation from Co²⁺ or S_n²⁻. Meanwhile, S_n²⁻ can accelerate the charge transfer, facilitating the OER process. Additionally, the presence of Mo⁴⁺ contributes to the stabilization of OER intermediates, thereby enhancing the efficiency of the OER process on CoOOH active sites. The hydrangea-like structure also offers plentiful active sites and efficient mass transfer. Besides, this electrolyzer obtains a current density of 10 mA cm⁻² at a cell voltage of 1.61 V.