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Photoelectrocatalytic seawater splitting is a promising low-cost method to produce green hydrogen in a large scale. The effects of Cl− ions in seawater on the performance of a photoanode have been reported in previous studies. However, few researches have been done on the roles of Cl− ions in a photocathode. Herein, for the first time, we find that Cl− ions in the electrolyte improve the photocurrent of a Si/In2S3 photocathode by 50% at −0.6 VRHE. An in-situ X-ray photoelectron spectroscopy (XPS) characterization combined with the time-of-flight secondary-ion mass spectrometry by simulating photoelectrochemical conditions was used to investigate the interface charge transfer mechanism. The results suggest that there is an In2+3S3−x(OH)2x layer on the surface of In2S3 in the phosphate buffer solution (PBS) electrolyte, which plays a role as an interface charge transfer mediator in the Si/In2S3 photocathode. The In2+3S3−x(OH)2x surface layer becomes In2+3S3−x(Cl)2x in the PBS electrolyte with NaCl and accelerates the charge transfer rate at the In2S3/electrolyte interface. These results offer a new concept of regulating interface charge transfer mediator to enhance the performance of photoelectrocatalytic seawater splitting for hydrogen production. [ABSTRACT FROM AUTHOR]

Interface charge transfer plays a key role in a photoelectrochemical cell. Recently, a faradaic junction transfer model was proposed that describes the interface charge transfer process. Electrochemical potential is introduced as a thermodynamic descriptor for the structure and composition of the surface faradaic layer of a semiconductor. However, the kinetic process in the faradaic junction model remains unclear. Herein, we introduce a descriptor, the density of storable charge (DOSC), to describe the number of charges that can be stored in a surface faradaic layer at different applied potentials. Moreover, the DOSC of the faradaic layer on the surface of Fe2O3 was modified by Ti doping, and the results suggest that a larger DOSC leads to higher transient photocurrent in a solar rechargeable device, which is helpful for designing other high-performance devices for solar conversion and storage. [ABSTRACT FROM AUTHOR]

A two-electrode solar rechargeable device is a potential low-cost method for solar energy conversion and storage. However, a low working voltage limits its practical application. It is significant to develop a solar rechargeable device with a high voltage. Herein, we report a device of BiVO4/CoPi/KPi(aq)/C with a working voltage of about 0.9 V, which is the highest value among all previously reported two-electrode devices. The high voltage comes from the positive onset potential of CoPi, which is used as the energy storage material for the first time. Moreover, we also investigate the reasons for the positive onset potential of CoPi by comparing with other conventional Co-based materials. The results suggest that CoPi has fewer tetrahedral Co(II), which leads to higher oxidation potential than the materials with more octahedral Co(II). This study highlights the importance of choosing energy storage materials with suitable potential windows in a solar rechargeable device and offers guidance to improve the performance. [ABSTRACT FROM AUTHOR]

Interface charge transfer plays a key role in the performance of semiconductors for different kinds of solar energy utilization, such as photocatalysis, photoelectrocatalysis, photochromism and photo-induced superhydrophilicity. In previous studies, different mechanisms have been used to understand interface charge transfer processes. However, the charge transfer mechanism at the solid/liquid interface remains a controversial topic. Here, taking TiO 2 as a model, we find and prove, via experiments, the new characteristic of photo-induced bipolarity of the surface layer (reduction faradaic layer and oxidation faradaic layer) on a semiconductor for the first time. Different from energy level positions in the classic surface states transfer mechanism, the potential window of a surface faradaic layer is located out of the forbidden band. Moreover, we find that the reduction faradaic layer and oxidation faradaic layer serve as electron and hole transfer mediators in photocatalysis, while the bipolarity or mono-polarity of the surface layer on a semiconductor depends on the applied potential in photoelectrocatalysis. The new characteristic of bipolarity can also offer new insights into the charge transfer process at the semiconductor/liquid interface for solar energy utilization., (© The Author(s) 2022. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd.)

Interfacial heterostructuring has appeared to be an efficient strategy to address the efficiency and applicability of the photocatalysts in solar energy conversion. Herein, we developed one-dimensional (1D) α-Fe 2 O 3 /TiO 2 nanoheterojunction arrays for enhanced photoelectrochemical (PEC) activity. α-Fe 2 O 3 nanotubes were firstly prepared via anodization under controlled hydrodynamic conditions to increase the efficiency. 1D α-Fe 2 O 3 /TiO 2 nanoheterojunction arrays were then prepared through a hydrothermal treatment and a subsequent annealing process. A controlled anodization by modulating the hydrodynamic conditions, added a fine coating of TiO 2 overlayer, to finally give an optimized composition and geometry for improved light absorption and spatial charge separation efficiency. Consequently, the optimized α-Fe 2 O 3 generated a photocurrent of 0.07 mA cm -2 (3.5 times higher than that of pristine α-Fe 2 O 3 ), and the as-obtained α-Fe 2 O 3 /TiO 2 nanoheterojunction exhibited a photocurrent intensity of 0.12 mA cm -2 (about 6 times higher than that of pristine α-Fe 2 O 3 ). A long-term stability can also be ensured. The well-controlled architectures provides a guideline for synthesis of advanced nanomaterials.