Decoupled Water Electrolysis via VO₂⁺/VO²⁺ Redox Mediator for 35 MPa High-Pressure Hydrogen Production

Abstract

Proton exchange membrane electrolysis cell (PEMEC) is highly anticipated for high-pressure hydrogen production, which can eliminate the mechanical gas compression process and thereby cut the capital expenditure cost. However, under high-pressure conditions, the H2 crossover could induce an increased H2 content in O2 to the explosion limits, which has hindered the development of high-pressure PEMEC. Herein, a decoupled water electrolysis (DWE) system consisting of a PEMEC for high-pressure H2 generation and an H-cell for low-pressure O2 generation was designed. The flowed electrolyte containing the VO2+/VO2+ redox couple was employed as the mediator. The DWE system could output H2 at a pressure of 35 MPa without H2–O2 mixing. At various current densities and cathodic pressures, the H2 crossover rate (rc) was evaluated. The rc was increased with the elevated pressure and decreased current densities and could reach nearly 1 mL min–1 cm–2 at 35 MPa when the circuit was disconnected. This work demonstrated the feasibility of the DWE system, which could offer a new horizon for high-pressure H2 production by PEM water electrolysis.