Charging Galvanic Cell for Rapid H2 Production in Neutral and/or Acidic Seawater

Abstract

The hydrogen evolution reaction (HER) in existing electrochemical processes is often coupled with thermodynamically forbidden anodic processes (e.g., water or organic electrooxidation), requiring high theoretical cell voltage to initialize the reaction. Besides, there exists a severe kinetic-mismatch issue. For instance, neutral or acidic conditions favor the kinetics of HER but are unfavorable for the kinetics of water oxidation, causing a high overpotential. Herein, we demonstrate that the thermodynamically spontaneous galvanic cell which involves the anodic electrooxidation of a metallic iron sheet (FeOR) and HER can be charged to enable low voltage and convenient hydrogen production in acidic or neutral seawater. At a pH of zero, the iR-compensated anodic potential needed to achieve a current density of 400 mA cm–2 is as low as −0.05 V (vs RHE), while in NaCl-saturated neutral water, the anodic potential needed to achieve a current density of 350 mA cm–2 is as low as 0.15 V (vs RHE). Additionally, the side products from the anodic FeOR are functional nanomaterials that could be separated easily, and their composition and structure can be flexibly manipulated by adjusting the formula of the electrolyte. Moreover, as no separator or anodic electrocatalyst is required, the setup for such FeOR-coupled hydrogen production can be greatly simplified. This work has demonstrated the workability and advantages of charging the thermodynamically spontaneous galvanic replacement reaction for efficient hydrogen production from acidic or neutral seawater.