Seon Woo Hwang

Propylene oxide (PO) is a key industrial chemical, often produced by epoxidizing propylene with H₂O₂ over titanium silicalite-1. However, current H₂O₂ production via the anthraquinone process relies on fossil-derived hydrogen, leading to substantial CO₂ emissions. Sustainable PO synthesis requires green H₂O₂ production. Here, we present a fully unassisted, solar- and bias-free system that generates H₂O₂. This platform enables modular, eco-friendly on-site PO synthesis by coupling formaldehyde oxidation with two-electron O₂ reduction under alkaline conditions. Efficient propylene epoxidation under these conditions is achieved using titanium silicalite-1 modified by introducing dinuclear titanium sites with Ti–O–Ti bonds, as revealed by density functional theory and instrumental analyses. The unassisted H₂O₂ production system is integrated with the modified titanium silicalite-1 to realize continuous PO production (1657 μmol_PO cm⁻² over 24 h), without electric or solar energy input. This unassisted PO production method can thus be energy-independent, offering a sustainable alternative to conventional processes.

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.