Three-in-one strategy for boosted charge transport in Ag/Co-Ni(OH)2 @nickel foam capacitive electrodes toward membrane-free electrocatalytic H2 production

Abstract

The cost-effective and scalable provision of H2 energy necessitates the development of a membrane-less electrolyzed water technique. In this study, we implemented a comprehensive three-in-one strategy to fabricate Ag/Co-Ni(OH)2 @nickel foam charge storage media, which were successfully employed to decouple the tightly coupled hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) steps, leading to efficient and membrane-less two-step water electrolysis. During the cathodic HER, we observed the concurrent oxidation of the Ni(OH)2 capacitive electrode to NiOOH while maintaining a consistent HER at a sustained current of 100 mA for 1800 s, together with a favorable operating potential of 1.43 V. Subsequently, the anodic OER encompassed the regenerations of Ni(OH)2 component, wherein NiOOH was specifically transformed back to Ni(OH)2, facilitating the O2-generation under a predetermined operating voltage of 0.31 V. In-situ Raman spectroscopy verified the reversible interconversion between the divalent nickel and trivalent nickel during step-1 of HER and step-2 of OER. Moreover, a Ni-Zn battery was conceived and constructed through the amalgamation of NiOOH and Zn sheets, effectively supplanting step-2 of the OER. This configuration enabled the uninterrupted integration of the H2-production and battery discharging step, presenting a novel and self-sustained approach for H2 production without the requirement of an external power supply.