Solar driven photoelectrochemical water splitting represents a promising approach for a sustainable and environmentally friendly production of renewable energy vectors and fuel sources, such as H ₂ .

TiO₂ nanofibers, TiO₂ hollow nanofibers, and nitridated TiO₂ hollow nanofibers were synthesized using a simple electrospinning method and subsequent nitridation treatment. The nitridated TiO₂ hollow nanofibers showed twice higher rate capability compared to that of pristine TiO₂ nanofibers at 5 C. This improvement is mainly attributed to shorter lithium ion diffusion length and high electronic conductivity along the surface of nitridated hollow nanofibers.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-Fe₂O₃ nanoflakes branched on TiO₂ nanotubes. The novel α-Fe₂O₃/TiO₂ hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO₂ nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO₂ are efficiently collected at FTO, while holes are transferred to the α-Fe₂O₃ nanobranches that serve as charge mediators to the electrolyte. The morphology of α-Fe₂O₃ that varies from ultrathin nanoflakes to nanorod/nanofiber structures depending on the Fe precursor concentration was shown to have a significant impact on the photo-induced activity of the α-Fe₂O₃/TiO₂ composites. In particular, it is shown that for an optimized photo-electrochemical structure, a combination of critical factors should be achieved such as (i) TiO₂ light absorption and photo-activation vs. α-Fe₂O₃-induced shadowing effect and (ii) the availability of free TiO₂ surface vs. α-Fe₂O₃-coated surface. Finally, theoretical analysis, based on DFT calculations, confirmed the optical properties experimentally determined for the α-Fe₂O₃/TiO₂ hierarchical nanostructures. We anticipate that this new multi-step hydrothermal process can be a blueprint for the design and development of other hierarchical heterogeneous metal oxide electrodes suitable for photo-electrochemical applications.

Germanium holds great potential as an anode material for lithium ion batteries due to its large theoretical energy density and excellent intrinsic properties related to its kinetics associated with lithium and electrons. However, the problem related to the tremendous volume change of Ge during cycling is the dominant obstacle for its practical use. The previous research has focused on the improvement in mechanics associated with lithium without consideration of the kinetics. In this study, we demonstrate that the configuration engineering of the Ge electrode enables the improvement in kinetics as well as favorable mechanics. Two types of Ge inverse opal structures with porous walls and dense walls were prepared using a confined convective assembly method and by adjusting Ge deposition parameters in a chemical vapor deposition system. The Ge inverse opal electrode with porous walls shows much improved electrochemical performances, especially cycle performance and rate capability, than the electrode with dense walls. These improvements are attributed to a large free surface, which offers a facile strain relaxation pathway and a large lithium flux from the electrolyte to the active material.