Fe(III)-cycle enhanced carbon oxidation reaction for low-energy hydrogen production via water electrolysis

Integrating the hydrogen evolution reaction (HER) with the carbon oxidation reaction (COR) is a promising method for producing H₂ with lower energy consumption. However, due to the passivation effect of oxygen functional groups (OFGs) for COR and Fe³⁺, achieving efficient and sustainable carbon oxidation to assist water electrolysis for hydrogen production remains a challenge over the past decades. This study introduced [EDTA·Fe(III)]^– as a mediator to promote COR. [EDTA·Fe(III)]^– effectively prevented the oxidation layer on the carbon surface from anchoring Fe (III) and reactivated the carbon that had been passivated by the oxidation layer. Density functional theory calculations indicated that the notable COR activity resulted from [EDTA·Fe(III)]^– effectively lowering the vertical ionization potential of carbon, without being affected by OFGs. Notably, in the HER||COR-[EDTA·Fe(III)]^– system, a cell voltage of merely 0.74 V is sufficient to reach a current density of 10 mA cm⁻², with the corresponding energy consumption being 1.76 kWh Nm⁻³ (H₂). This strategy offers new insights into achieving stable, low-energy hydrogen production via water electrolysis.