MnO2 regulated potential window and storage capacity of CoxNi1-x(OH)2@MnO2 freestanding electrode for promoted membrane-less and decoupled water splitting

The realization of membrane-less and decoupled water splitting holds immense significance in facilitating cost-efficient and substantial H2 supply. In this study, a two-step hydrothermal reaction was employed to synthesize a CoxNi1-x(OH)2@MnO2 freestanding electrode, utilizing nickel foam (NF) as the substrate, MnO2 as the seed layer, and CoxNi1-x(OH)2 nanofiber as the surface layer. This fabrication approach resulted in a buffer electrode with an expanded potential window and enhanced charge storage capacity. Notably, the optimized CoxNi1-x(OH)2@MnO2@NF electrode functioned as an effective charge mediator, successfully decoupling the synchronous oxygen and hydrogen evolution reactions (OER and HER). Consequently, the need for separators was eliminated, introducing a novel two-step water electrolysis hydrogen production technology. Remarkably, the initial HER process at the cathode exhibited robust performance, sustaining a current of 100 mA for an impressive duration of 1500 s. Simultaneously, the CoxNi1-x(OH)2@MnO2 mediator underwent oxidation, attaining its corresponding oxidation state and yielding a commendable applied potential of 1.564 V. Subsequently, the OER step entailed the revival of the buffer electrode, enabling the facilitated production of anodic O2 at an operating potential of 0.392 V. Beyond that, the integration of an oxidizing buffer medium and a zinc foil enabled the development of a battery configuration, effectively replacing the second step of OER. This pioneering integration facilitated the concurrent realization of persistent H2 generation and battery discharging, presenting an innovative approach to hydrogen production that circumvents reliance on an external power supply. Thus, this decoupled HER-OER apparatus offers a propitious strategy for effectively converting renewable resources into hydrogen.