Combining water reduction and liquid fuel oxidization by nickel hydroxide for flexible hydrogen production

Abstract

Electrochemical water splitting, which depends on the simultaneous hydrogen and oxygen evolution, is being considered as a sustainable hydrogen production approach, but where oxygen is generally an unconsidered by-product because of its rich existence in ambient (except some specific applications). The oxygen evolution related issues, including gas separation, sluggish kinetics, over-potential and noble catalyst, also limit the application of this technology. Herein, using nickel hydroxide as a solid-state redox mediator, we combine the water reduction and the oxidization of liquid fuel (e.g. ethanol, methanol, formate, isopropanol or hypophosphite solution) to form a new electrolysis architecture for hydrogen production without above issues. The hydrogen production involves the cathodic water reduction and the anodic oxidization of Ni(OH)2 → NiOOH, and consequently the cathodic reduction of NiOOH → Ni(OH)2 is coupled with the anodic oxidization of liquid fuel to form a hybrid system for delivering stable electricity energy and recycling Ni(OH)2.