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

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.