CoMn2O4/Co(OH)2 anchored on a MoS2/MWCNT scaffold: a robust electrocatalyst for low overpotential and high current density water electrolysis

Abstract

Electrochemical water splitting using earth-abundant materials is often hindered by slow oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) kinetics, as well as instability at practical current densities. In this study, we developed a hierarchically structured CoMn₂O₄/Co(OH)₂/MoS₂/MWCNT (CDMC) nanocomposite designed to integrate redox-active Co-based oxide/hydroxide domains, edge-rich MoS₂, and a highly conductive MWCNT scaffold within a single architecture characterized by multiple heterointerfaces. The CDMC electrode demonstrates impressively low overpotentials of 164 mV for the oxygen evolution reaction and 198 mV for the hydrogen evolution reaction at a current density of 50 mA cm⁻², achieving Tafel slopes of 56 and 130 mV dec⁻¹, respectively. These results surpass those of all control compositions and many state-of-the-art non-noble catalysts. In a two-electrode configuration, overall water splitting in 1 M KOH is realized at 1.75 V while sustaining 50 mA cm⁻², paired with high turnover frequencies for both half-reactions, robust long-term stability, and a faradaic efficiency of approximately 88.5%. The electrochemical performance of the composite is discussed by correlating the electrochemically active surface area (ECSA), double-layer capacitance, and impedance analysis, and the boosted activity is attributed to the augmented charge transport mechanism and efficient usage of the active sites, rather than the geometrical surface area. These results make the CDMC composite a good bifunctional material for alkaline electrolyzers and help in achieving sustainable hydrogen production.