MXene-Coupled Sulfurization Strategy for MnCo2O4/MnCo2S4 Heterojunctions for Enhanced Overall Water Splitting

Abstract Developing low-cost and durable electrocatalysts with engineered heterogeneous interfaces to accelerate reaction kinetics remains a critical yet challenging path for advancing efficient water electrolysis. In this study, we present a facile two-step hydrothermal strategy for the fabrication of MnCo2O4/MnCo2S4 nanoarrays integrated with MXene nanosheets. Comprehensive experimental characterizations reveal that the incorporation of MXene significantly enhances the electronic conductivity and interfacial charge-transfer capability of the hybrid architecture, thereby facilitating water dissociation kinetics and boosting intrinsic electrocatalytic activity. Benefiting from the synergistic coupling among MnCo2O4, MnCo2S4, and MXene, the optimized MnCo2O4/MnCo2S4@MXene exhibits outstanding bifunctional electrocatalytic performance in 1.0 M KOH. The catalyst requires ultralow overpotentials of only 155.2 mV for HER and 216.6 mV for OER to achieve 10 mA cm–2. Remarkably, an overpotential of 288.4 mV is needed to deliver 50 mA cm–2 for the OER process. When the MnCo2O4/MnCo2S4@MXene heterostructure is employed as the cathode and anode as a noble metal-free overall water-splitting system, the assembled electrolyzer delivers a low cell voltage of 1.56 V at 10 mA cm–2, closely comparable to that of the benchmark RuO2//Pt/C device (1.53 V). In addition, the electrolyzer demonstrates excellent operational durability over 100 h of continuous electrolysis. The DFT results demonstrate that charge transfer from MCO/MCS to MXene modulates the electronic structure of the heterostructure, leading to enhanced electronic conductivity and accelerated charge-transport kinetics. These findings highlight the significant potential of interfacial MXene-engineered spinel/sulfide heterostructures as efficient and economically viable electrocatalysts for sustainable hydrogen production.