Two-step fabrication of hierarchical Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle array for highly efficient decoupled water splitting

The temporal and spatial segregation of the hydrogen and oxygen evolution reactions (HER and OER) are essential for advancing membrane-free electrolysis technology in H 2 production through water splitting. This investigation employed a two-step fabrication approach to craft a three-dimensional self-supporting buffered electrode. This method involved utilizing a Ni(OH) 2 @NiCo 2 O 4 core-shell nanoneedle array as the active material and nickel foam (NF) as the substrate. Remarkably, the H 2 production at the cathode displayed remarkable efficiency, maintaining an uninterrupted operation duration of 1500 s at a current of 100 mA. Simultaneously, the Ni(OH) 2 @NiCo 2 O 4 mediator on the anodic electrode underwent oxidation during this process, leading to the generation of its respective oxidized state, accompanied by a noteworthy operating voltage of 1.50 V. Afterwards, the second step of the OER involved the recovery of the buffered electrode and the generation of O 2 at an operational voltage of 0.46 V, with the O 2 -production duration being equivalent to that of the first step in the HER process. Interestingly, the revival process of the buffered electrode in the second step can also be coupled with zinc sheets, thereby constructing a battery. During the discharge process of the battery, the regeneration of the buffered electrode was achieved, and this discharge process could also provide a power supply for the first step of H 2 -evolution. Therefore, this decoupled water electrolysis system presents a promising avenue for facilitating the effective transformation of renewable sources into hydrogen.