Bias-free photoelectrochemical system mediates hydrogen production and biomass conversion at high current density

Abstract

The construction of a bias-free photoelectrochemical (PEC) system is a promising approach to producing renewable fuels and chemicals from solar energy. However, the conventional anodic reaction of oxygen evolution reaction (OER) possesses slow kinetics and a large overpotential. In this study, 5-Hydroxymethylfurfural (HMF) oxidation on a Cu-based anode is introduced to be paired with a cathodic HER on p-Si/CdS/Pt photocathode. Due to the semi-oxidized structure of Cu+, the anode Cu2O-CF achieves an onset potential of 0.05 V vs RHE and ∼100% FEHMFCA under ∼80 mA/cm2, which reduces the anodic potential by ∼1.6 V compared with OER. The p-Si based heterojunction photocathode exhibits an onset potential of 0.45 V vs RHE and a photocurrent of ∼30 mA/cm2 (0 V vs RHE), providing a large photovoltage of 450 mV. As a result, the tandem configuration can achieve bias-free anodic FEHMFCA of 84% and cathodic FEH2 of 95% at 15 mA/cm2 after optimizing the compatibility of the cathode and anode. This strategy provides a new possibility for the construction of an unbiased photo-assisted solar-to-chemical system.