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The disproportionation of H₂O into solar fuels H₂and O₂, or water splitting, is a promising strategy for clean energy harvesting and storage but requires the concerted action of absorption of photons, separation of excitons, charge diffusion to catalytic sites and catalysis of redox processes. It is increasingly evident that the rational design of photocatalysts for efficient water splitting must employ hybrid systems, where the different components perform light harvesting, charge separation and catalysis in tandem. In this topical review, we report on the recent development of a new class of hybrid photocatalysts that employs M_xV₂O₅(M = p-block cation) nanowires in order to engineer efficient charge transfer from the photoactive chalcogenide quantum dots (QDs) to the water-splitting and hydrogen evolving catalysts. Herein, we summarize the oxygen-mediated lone pair mechanism used to modulate the energy level and orbital character of mid-gap states in the M_xV₂O₅nanowires. The electronic structure of M_xV₂O₅is discussed in terms of density functional theory and hard x-ray photoelectron spectroscopy (HAXPES) measurements. The principles of HAXPES are explained within the context of its unique sensitivity to metal 5(6)s orbitals and ability to non-destructively study buried interface alignments of quantum dot decorated nanowires i.e., M_xV₂O₅/CdX (X = S, Se, Te). We illustrate with examples how the M_xV₂O₅/CdX band alignments can be rationally engineered for ultra-fast charge-transfer of photogenerated holes from the quantum dot to the nanowires; thereby suppressing anodic photo-corrosion in the CdX QDs and enabling efficacious hydrogen evolution.

Straining the vanadium dimers along the rutilec‐axis can be used to tune the metal‐to‐insulator transition (MIT) of VO₂but has thus far been limited to TiO₂substrates. In this work VO₂/MgF₂epitaxial films are grown via molecular beam epitaxy (MBE) to strain engineer the transition temperature (T_MIT). First, growth parameters are optimized by varying the synthesis temperature of the MgF₂(001) substrate (T_S) using a combination of X‐ray diffraction techniques, temperature dependent transport, and soft X‐ray photoelectron spectroscopy. It is determined thatT_Svalues greater than 350 °C induce Mg and F interdiffusion and ultimately the relaxation of the VO₂layer. Using the optimized growth temperature, VO₂/MgF₂(101) and (110) films are then synthesized. The three film orientations display MITs with transition temperatures in the range of 15–60 °C through precise strain engineering.

Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi‐electron cathode material, KVOPO₄, for sodium ion batteries. Due to the unique polyhedral framework, the V³⁺↔ V⁴⁺↔ V⁵⁺redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO₄based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na⁺per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg⁻¹. Combining an average voltage of 2.56 V vs. Na/Na⁺, a high practical energy density of over 600 Wh kg⁻¹was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO₄framework is a 3D ionic conductor with a reasonably, low Na⁺migration energy barrier of ≈450 meV, in line with the good rate capability obtained.