MgCo₂O₄@NiCo layered double hydroxide core-shell composite as a high-capacity redox mediator for sustainable...

The spatiotemporal decoupling of the hydrogen and oxygen evolution reactions (HER and OER) is essential for membrane-free, decoupled water electrolysis. However, the advancement of this technology faces persistent challenges due to the scarcity of reliable redox mediator (RM) electrodes. Herein, using a three-step hydrothermal-annealing-electrodeposition strategy, we developed a three-dimensional self-supported core-shell heterostructure of MgCo₂O₄@NiCo layered double hydroxide (LDH) on nickel foam (NF) as a high-performance RM electrode. The MgCo₂O₄ nanoneedle substrate enhances electrical conductivity and structural robustness, while the NiCo-LDH nanosheets provide abundant electroactive sites. Synergistic interactions between these components enable the electrode to achieve a high specific capacitance of 2091 ± 12 F g^-1 under 5 mA cm^-2. In the decoupled electrolysis system, this RM electrode separates water splitting into two distinct stages: HER at 1.39 V and OER at 0.33 V. Moreover, the electrode demonstrates excellent redox reversibility and maintains robust structural integrity over extended cycling. This study proposes a feasible approach for engineering high-performance RM electrodes, paving the way for secure generation of hydrogen from intermittent renewable energy sources.