The cathodic material plays an essential role in oxygen reduction reaction for energy conversion and storage systems. Titanium dioxide, as a semiconductor material, is usually not recognized as an efficient oxygen reduction electrocatalyst owning to its low conductivity and poor reactivity. Here we demonstrate that nano-structured titanium dioxide, self-doped by oxygen vacancies and selectively exposed with the high-energy {001} facets, exhibits a surprisingly competitive oxygen reduction activity, excellent durability and superior tolerance to methanol. Combining the electrochemical tests with density-functional calculations, we elucidate the defect-centred oxygen reduction reaction mechanism for the superiority of the reductive {001}-TiO_2−x nanocrystals. Our findings may provide an opportunity to develop a simple, efficient, cost-effective and promising catalyst for oxygen reduction reaction in energy conversion and storage technologies.

Developing eco-friendly catalysts for effective water purification with minimal oxidant use is imperative. Herein, we present a metal-free and nitrogen/fluorine dual-site catalyst, enhancing the selectivity and utilization of singlet oxygen (¹O₂) for water decontamination. Advanced theoretical simulations reveal that synergistic fluorine-nitrogen interactions modulate electron distribution and polarization, creating asymmetric surface electron configurations and electron-deficient nitrogen vacancies. These properties trigger the selective generation of ¹O₂ from peroxymonosulfate (PMS) and improve the utilization of neighboring reactive oxygen species, facilitated by contaminant enrichment at the fluorine-carbon Lewis-acid adsorption sites. Utilizing these insights, we synthesize the catalyst through montmorillonite (MMT)-assisted pyrolysis (NFC/M). This method leverages the role of MMT as an in-situ layer-stacked template, enabling controlled decomposition of carbon, nitrogen, and fluorine precursors and resulting in a catalyst with enhanced structural adaptability, reactive site accessibility, and mass-transfer capacity. The NFC/M demonstrates an impressive 290.5-fold increase in phenol degradation efficiency than the single-site analogs, outperforming most of metal-based catalysts. This work not only underscores the potential of precise electronic and structural manipulations in catalyst design but also advances the development of efficient and sustainable solutions for water purification.

Metal oxide semiconductors with surface homojunctions characteristic of continuous band bending and well-defined epitaxial interfaces show amazing potential for photocatalytic applications. Herein, a new concept of facet junctions is proposed and validated according to the synergy between the co-exposed crystal facets of shape-tailored anatase TiO₂ single crystals. By considering the atomic and electronic interactions between the co-exposed facets, our density functional theory calculations reveal the existence of type-II band alignment between the co-exposed {001} and {101} facets. This band alignment results in in situ construction of a facet junction to allow built-in facet-mediated carrier transfer. The self-constructed {101}/{001} facet junction, due to the effective carrier separation between different exposed facets, exhibits a significantly enhanced quantum efficiency and catalytic performance in photochemical hydrogen generation compared to TiO₂ poly-crystals. These findings open a new horizon of facet junction-engineered nano-catalysts for more robust and efficient energy and environmental applications.

Metal sulfide semiconductors, such as molybdenum disulfide (MoS₂) and bismuth trisulphide (Bi₂S₃), are of considerable interest for their excellent applications in photocatalysis and in many other fields. However, the controllable synthesis of MoS₂/Bi₂S₃ hybrid nanostructures remains a challenge. In this study, we report a unique sacrificial templating strategy for preparing layer-controlled MoS₂ on three-dimensional (3D) Bi₂S₃ micro-flowers. For this approach, Bi₂S₃ was utilized as a sacrificial template to regulate the ion exchange, and the dosage of molybdenum was adjusted to tune the dynamic formation, thus converting the MoS₂ nanosheets on the Bi₂S₃ micro-flowers from monolayer to multilayer. Such a 3D flower-like hybrid nanostructure enables MoS₂/Bi₂S₃ to exhibit adsorption-promoted photocatalysis under visible light irradiation, especially for the excellent photodegradation of low-concentration organic pollutants, for example, azo dye and atrazine. The observed superiority of the 3D MoS₂/Bi₂S₃ was mainly attributed to the increased mass transfer, robust light-harvesting capacity, improved charge separation, lower oxygen-activation barrier and enhanced active oxygen yield. Our findings are of interest for the development of novel S-based photocatalysts and provide a new opportunity to efficiently remove low-concentration refractory pollutants.