Self-enhanced localized alkalinity at the S-rich MoS2+x cathode for superb photovoltaic-driven electrocatalytic uranium extraction.

Reducing soluble U(VI) to insoluble U(IV) is an efficient uranium extraction strategy. However, the two axial oxygen atoms in uranyl (UO22 +) create a kinetic barrier to electron transfer, hindering U(VI) reduction. Here, we present an innovative strategy that leverages the hydrogen evolution reaction (HER) to generate a localized alkaline microenvironment at the catalyst surface; OH⁻ accumulation rapidly precipitates UO22⁺ as insoluble UO2(OH)2, enabling efficient uranium extraction from water. In this process, the S-rich hollow MoS2+x with high HER activity, which was derived from the Mo-MOF grown on carbon felt (CF), was used as the cathode (MoS2+x/CF) in a photovoltaic-driven electrocatalytic system. The anode consists of a TiO2 nanorod array on FTO glass, coupled with a rear-mounted silicon solar cell. Due to the localized alkaline microenvironment formed by the HER on the MoS2+x/CF cathode surface, this electrocatalytic system achieves 99.8% uranium removal from uranium-containing wastewater within 30 min of illumination. Density functional theory (DFT) calculations and experimental results confirm that unsaturated edge S atoms in MoS2+x significantly enhance HER activity. Additionally, the electron transfer between uranium and edge S enhances uranium adsorption and promotes its interfacial reaction with OH*. This work opens new perspectives for uranium extraction from aqueous solutions.