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The present work describes a self-assembling photocatalytic system that is observed when illuminating grey titania nanoparticles in suspension with a plain aqueous Ni2+ solution. Such a suspension (in contrast to white titania), under UV illumination, increasingly produces H2 from neutral water. We show that the origin of this self-activation is not the light-induced deposition of Ni0 or another Ni-catalyst compound on the titania surface. Rather, in-situ electron paramagnetic resonance (EPR) clearly indicates that the activation is due to a light-induced formation of a suitable defect structure (Ti3+-OV) on grey titania, combined with the formation of an intermediate monovalent nickel (Ni(I)) electron transfer relay. Remarkably, the resulting Ni+/TiO2/Ti3+ photocatalyst operates in absence of any noble metal or sacrificial agent.

Titanium oxide (TiO2) and iron oxide (α-Fe2O3) hematite films have potential applications as photoanodes in electrochemical water splitting. In the present work TiO2 and α-Fe2O3 thin films were prepared by two methods, e.g., sol-gel and High Power Impulse Magnetron Sputtering (HiPIMS) and judged on the basis of physical properties such as crystalline structure and surface topography and functional properties such as simulated photoelectrochemical (PEC) water splitting conditions. It was revealed that the HiPIMS method already provides crystalline structures of anatase TiO2 and hematite Fe2O3 during the deposition, whereas to finalize the sol-gel route the as-deposited films must always be annealed to obtain the crystalline phase. Regarding the PEC activity, both TiO2 films show similar photocurrent density, but only when illuminated by UV light. A different situation was observed for hematite films where plasmatic films showed a tenfold enhancement of the stable photocurrent density over the sol-gel hematite films for both UV and visible irradiation. The superior properties of plasmatic films could be explained by ability to address some of the hematite drawbacks by the deposition of very thin films (25 nm) consisting of small densely packed particles and by doping with Sn.

Potassium‐ion batteries (KIBs) have attracted enormous attention as a next‐generation energy storage system due to their low cost, fast ionic conductivity within electrolytes, and high operating voltage. However, developing suitable electrode materials to guarantee high‐energy output and structural stability to ensure long cycling performance remains a critical challenge. Herein, anatase TiO2 nanoparticles are encapsulated in nitrogen‐rich graphitic carbon (TiO2@NGC) with hierarchical pores and high surface area (250 m2 g−1) using the Ti‐based metal–organic framework NH2‐MIL‐125 (Ti8O8(OH)4(NH2‐bdc)6 with NH2‐bdc2− = 2‐amino‐1,4‐benzenedicarboxylate) as a sacrificial template. Serving as the anode material in a K‐ion half‐cell, TiO2@NGC delivers a high capacity of 228 mA h g−1 with remarkable cycling performance (negligible loss over 2000 cycles with more than 98% Coulombic efficiency). The charge‐storing mechanism is underpinned using ex situ characterization techniques such as ex situ X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. It is revealed that the original TiO2 phase gets transformed to the anorthic Ti7O13 and monoclinic K2Ti4O9 phase after the first charge/discharge cycle, which further initiates the charge storage process via the conversion reactions.

Summary: Here, we evaluate three different noble metal co-catalysts (Pd, Pt, and Au) that are present as single atoms (SAs) on the classic benchmark photocatalyst, TiO2. To trap the single atoms on the surface, we introduced controlled surface vacancies (Ti3+-Ov) on anatase TiO2 nanosheets by a thermal reduction treatment. After anchoring identical loadings of single atoms of Pd, Pt, and Au, we measure the photocatalytic H2 generation rate and compare it to the classic nanoparticle co-catalysts on the nanosheets. While nanoparticles yield the well-established the hydrogen evolution reaction activity sequence (Pt > Pd > Au), for the single atom form, Pd radically outperforms Pt and Au. Based on density functional theory (DFT), we ascribe this unusual photocatalytic co-catalyst sequence to the nature of the charge localization on the noble metal SAs embedded in the TiO2 surface.