Coupling furfural oxidation for bias-free hydrogen production using crystalline silicon photoelectrodes.

To commercialize the technology of photoelectrochemical hydrogen production, it is essential to surpass the US. Department of Energy target of 0.36 mmol h^-1 cm^-2 for 1-sun hydrogen production rate. In this study, we utilize crystalline silicon, which can exhibit the highest photocurrent density (43.37 mA cm^-2), as the photoelectrode material. However, achieving bias-free water splitting (>1.6 V) remains challenging due to the intrinsic low photovoltage of crystalline silicon (0.6 V). To address this limitation, we replace water oxidation with low-potential furfural oxidation, enabling not only bias-free hydrogen production but also dual hydrogen production at both the cathodic and anodic sides. This approach results in a record 1-sun hydrogen production rate of 1.40 mmol h^-1 cm^-2, exceeding the Department of Energy target by more than fourfold.