Anatase and rutile mixed-phase TiO₂ with an ideal ratio has been proven to significantly enhance photoelectrochemical (PEC) activity in water-splitting applications due to suppressing the electron–hole recombination. However, the mechanism of this improvement has not been satisfactory described yet. The PEC water oxidation (oxygen evolution) at the interface of TiO₂ photoanode and electrolyte solution is determined by the fraction of the photogenerated holes that reach the solution and it is defined as the hole transfer efficiency. The surface and bulk recombination processes in semiconductor photoanodes majorly influence the hole transfer efficiency. In this work, we study the hole transfer process involved in mixed-phase TiO₂ nanotube arrays/solution junction using intensity-modulated photocurrent and photovoltage spectroscopy (IMPS and IMVS); then, we correlate the obtained hole transfer rate constants to (photo)electrochemical impedance spectroscopy (PEIS) measurements. The results suggest that the enhanced performance of the TiO₂ mixed-phase is due to the improved hole transfer rate across the TiO₂/liquid interface as well as to the decrease in the surface trap recombination of the holes.

Optimizing the reactivity and selectivity of single‐atom catalysts (SACs) remains a crucial yet challenging issue in heterogeneous catalysis. This study demonstrates selective catalysis facilitated by a polyoxometalates‐mediated electronic interaction (PMEI) in a Pt single‐atom catalyst supported on CeO ₂ modified with Keggin‐type phosphotungstate acid (HPW), labeled as Pt ₁ /CeO ₂ ‐HPW. The PMEI effect originates from the unique arrangement of isolated Pt atoms and HPW clusters on the CeO ₂ support. Electrons are transferred from the ceria support to the electrophilic tungsten in HPW clusters, and subsequently, Pt atoms donate electrons to the now electron‐deficient ceria. This phenomenon enhances the positive charge of Pt atoms, moderating O ₂ activation and limiting lattice oxygen mobility compared to the conventional Pt ₁ /CeO ₂ catalyst. The resulting electronic structure of Pt combined with the strong and local acidic environment of HPW on Pt ₁ /CeO ₂ ‐HPW leads to improved efficiency and N ₂ selectivity in the degradation of NH ₃ and NO, as well as increased CO ₂ yield when inputting volatile organic compounds. This study sheds the light on the design of SACs with balanced reactivity and selectivity for environmental catalysis.

Multi-leg TiO ₂ nanotubes have been synthesised by electrochemical anodisation of Ti foils with suitable optimisation of the electrolyte (containing NH ₄ F and HF) composition and concentration. As a result, multi-leg nanotube morphology shows a 4-fold enhancement in photocurrent density compared with that of compact tubes of comparable length under UV-VIS (320–500 nm) light illumination. We attribute this enhancement in photocurrent to efficient light scattering within the multi-leg morphology and the availability of a large contact area with the electrolyte compared to that of compact nanotubes. A model has been presented for light trapping and scattering ability on the basis of the graded refractive index behaviour associated with multi-leg nanotubes. Such graded refractive index behaviour is found to reduce specular reflectance, leading to a greater scattering of light into the nanotube structure. The diffused reflectance spectra confirm higher scattering in the multi-leg nanotube arrays, which indicates greater light harvesting by the multi-leg nanotube arrays.

Defects play a crucial role in shaping the efficiency and performance of semiconductor‐based technologies. Under illumination, the interaction between photo‐excited charge carriers and defect states in the semiconductor can significantly influence the response of devices and catalysts. Here, an X‐ray photoelectron spectroscopy study conducted under light excitation is presented to track exciton generation and its interaction with defects in CeO ₂ , a widely used metal‐oxide support in (photo) catalysis. The light intensity‐dependent measurements reveal that photo‐excited electrons in CeO ₂ can effectively reduce Ce ⁴⁺ to Ce ³⁺ . Surface‐enhanced Raman spectroscopy further highlights the critical role of Ce ³⁺ states in governing charge and energy transport across the CeO ₂ ‐molecule interface. Finally, how these photo‐induced states (Ce ³⁺ ) can be leveraged is demonstrated to control the selectivity in the photocatalytic CO ₂ reduction reaction, dramatically influencing the yields of CO, CH ₄ , and H ₂ .

Transfer of semiconductor thin films on transparent and or flexible substrates is a highly desirable process to enable photonic, catalytic, and sensing technologies. A promising approach to fabricate nanostructured TiO₂ films on transparent substrates is self-ordering by anodizing of thin metal films on fluorine-doped tin oxide (FTO). Here, we report pulsed direct current (DC) magnetron sputtering for the deposition of titanium thin films on conductive glass substrates at temperatures ranging from room temperature to 450 °C. We describe in detail the influence that deposition temperature has on mechanical, adhesion and microstructural properties of titanium film, as well as on the corresponding TiO₂ nanotube array obtained after anodization and annealing. Finally, we measure the photoelectrochemical water splitting activity of different TiO₂ nanotube samples showing that the film deposited at 150 °C has much higher activity correlating well with the lower crystallite size and the higher degree of self-organization observed in comparison with the nanotubes obtained at different temperatures. Importantly, the film showing higher water splitting activity does not have the best adhesion on glass substrate, highlighting an important trade-off for future optimization.