Atomically dispersed asymmetric U-O-Ti enhanced photoelectrochemical oxygen evolution reaction

In pursuit of carbon neutrality goals, nuclear energy, as a stable low-carbon baseload power source, constitutes a critical component of the global energy structure transition. Concurrently, photoelectrochemical (PEC) water splitting for green hydrogen production represents a pivotal technology for renewable energy conversion and the practical realization of carbon neutrality. In PEC water splitting systems, the OER occurring at the photoanode involves a sluggish four-electron transfer process with high overpotential, constituting the primary bottleneck limiting overall energy conversion efficiency. As a classic n-type semiconductor photoanode material, TiO₂ has been extensively studied owing to its excellent chemical stability and low cost. However, its practical large-scale application is severely constrained by a wide bandgap, severe photogenerated carrier recombination, and insufficient intrinsic OER activity. Meanwhile, the substantial quantities of depleted uranium and uranium-containing wastewater generated by the nuclear industry chain pose urgent environmental and resource challenges requiring resolution. Although uranium's unique 5f orbital hybridization characteristics and multivalent redox capabilities endow it with significant potential for catalytic applications, research on the application and underlying mechanisms of uranium-based materials in the field of PEC water splitting remains scarce.

Photo-assisted catalysis technology can accelerate reaction kinetics through photogenerated carriers. However, traditional powdered nanocatalysts suffer from insufficient exposure of active sites and difficulties in recovery and reuse, while depleted uranium resources lack safe, high-value-added utilization pathways. Addressing these industrial challenges, Professor Wenkun Zhu and Professor Tao Chen’s research group innovatively proposed a catalytic design strategy based on the covalent regulation of actinide 5f orbitals. Employing a photodeposition method with uranium-containing wastewater directly as the uranium source, the team successfully anchored uranium single atoms in situ onto TiO₂ nanorod arrays rich in oxygen vacancies, constructing atomically asymmetric U−O−Ti bimetallic active sites. This approach simultaneously achieves the resource recovery of uranium from uranium-containing wastewater and the realization of high-efficiency PEC OER catalysis.

The research results demonstrate that under simulated solar illumination (AM 1.5G) in 1 mg L⁻¹ NaOH electrolyte, the as-fabricated U/TiO₂ NRA photoanode achieves a photocurrent density of 3.25 mA cm⁻² at 1.23 V vs. RHE, representing a 3.82-fold enhancement compared to the pristine TiO₂ photoanode. This performance substantially exceeds that of most previously reported TiO₂-based PEC photoanode materials. The material exhibits an incident photon-to-electron conversion efficiency (IPCE) of 54.5% at 380 nm and achieves a maximum applied bias photon-to-current efficiency (ABPE) of 1.35% at 0.63 V vs. RHE. During continuous stability testing over 50 h, the photocurrent density shows negligible decay, and the uranium leaching concentration after reaction remains well below the United States drinking water standard, demonstrating excellent structural stability and operational safety.

Through in situ FTIR, X-ray absorption fine structure characterization, and theoretical calculations, the research team systematically elucidated the catalytic enhancement mechanism of the U−O−Ti bimetallic sites. In situ FTIR real-time tracking confirmed that the U−O−Ti bimetallic sites significantly promote the adsorption and enrichment of the key OER intermediate *OOH on the material surface, providing a highly active interface for the reaction. Density functional theory (DFT) calculations revealed that the strong oxophilic nature of U renders the 2O_ads−U−3O_latt configuration the central reaction core for H₂O activation. Through electronic transfer, this configuration synergistically enhances the capability of adjacent Ti sites to capture reaction intermediates, creating a spatial synergistic effect. The effective hybridization of U 5f orbitals with O 2p and Ti 3d orbitals not only narrows the material bandgap, broadens the light response range, and promotes photogenerated carrier separation, but also reduces the energy barrier of the OER rate-determining step (*OOH formation) to 1.04 eV, substantially lower than that of pristine TiO₂ (1.16 eV), thereby significantly accelerating OER reaction kinetics.

This research not only opens a new avenue for the high-value resource utilization of depleted uranium and uranium-containing wastewater but also fully exploits the catalytic potential of actinide 5f orbitals, thereby expanding the application boundaries of actinide materials in the field of energy catalysis. This work provides a novel theoretical foundation and technological strategy for the design and development of high-performance PEC photoanode materials.

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