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

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 H-2 crossover could induce an increased H-2 content in O-2 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 H-2 generation and an H-cell for low-pressure O-2 generation was designed. The flowed electrolyte containing the VO2+/VO2+ redox couple was employed as the mediator. The DWE system could output H-2 at a pressure of 35 MPa without H-2-O-2 mixing. At various current densities and cathodic pressures, the H-2 crossover rate (r(c)) was evaluated. The r(c) 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 H-2 production by PEM water electrolysis.