A transparent CdS@TiO2 nanotextile photoanode with boosted photoelectrocatalytic efficiency and stability

Recent Progress in Interface Engineering of Nanostructures for Photoelectrochemical Energy Harvesting Applications

With rapid and continuous consumption of nonrenewable energy, solar energy can be utilized to meet the energy requirement and mitigate environmental issues in the future. To attain a sustainable society with an energy mix predominately dependent on solar energy, photoelectrochemical (PEC) device, in which semiconductor nanostructure-based photocatalysts play important roles, is considered to be one of the most promising candidates to realize the sufficient utilization of solar energy in a low-cost, green, and environmentally friendly manner. Interface engineering of semiconductor nanostructures has been qualified in the efficient improvement of PEC performances including three basic steps, i.e., light absorption, charge transfer/separation, and surface catalytic reaction. In this review, recently developed interface engineering of semiconductor nanostructures for direct and high-efficiency conversion of sunlight into available forms (e.g., chemical fuels and electric power) are summarized in terms of their atomic constitution and morphology, electronic structure and promising potential for PEC applications. Extensive efforts toward the development of high-performance PEC applications (e.g., PEC water splitting, PEC photodetection, PEC catalysis, PEC degradation and PEC biosensors) are also presented and appraised. Last but not least, a brief summary and personal insights on the challenges and future directions in the community of next-generation PEC devices are also provided.

A coating strategy to achieve effective local charge separation for photocatalytic coevolution

Semiconductors of narrow bandgaps and high quantum efficiency have not been broadly utilized for photocatalytic coevolution of H₂ and O₂ via water splitting. One prominent issue is to develop effective protection strategies, which not only mitigate photocorrosion in an aqueous environment but also facilitate charge separation. Achieving local charge separation is especially challenging when these reductive and oxidative sites are placed only nanometers apart compared to two macroscopically separated electrodes in a photoelectrochemical cell. Additionally, the driving force of charge separation, namely the energetic difference in the barrier heights across the two type of sites, is small. Herein, we used conformal coatings attached by nanoscale cocatalysts to transform two classes of tunable bandgap semiconductors, i.e., CdS and GaInP₂, into stable and efficient photocatalysts. We used hydrogen evolution and redox-mediator oxidation for model study, and further constructed a two-compartment solar fuel generator that separated stoichiometric H₂ and O₂ products. Distinct from the single charge-transfer direction reported for conventional protective coatings, the coating herein allows for concurrent injection of photoexcited electrons and holes through the coating. The energetic difference between reductive and oxidative catalytic sites was regulated by selectivity and local kinetics. Accordingly, the charge separation behavior was validated using numerical simulations. Following this design principle, the CdS/TiO₂/Rh@CrO_x photocatalysts evolved H₂ while oxidizing reversible polysulfide redox mediators at a maximum rate of 90.6 μmol⋅h^-1⋅cm^-2 by stacking three panels. Powered by a solar cell, the redox-mediated solar water-splitting reactor regenerated the polysulfide repeatedly and achieved solar-to-hydrogen efficiency of 1.7%.

Amorphous inorganic semiconductors for the development of solar cell, photoelectrocatalytic and photocatalytic applications

Amorphous inorganic semiconductors have attracted growing interest due to their unique electrical and optical properties that arise from their intrinsic disordered structure and thermodynamic metastability. Recently, amorphous inorganic semiconductors have been applied in a variety of new technologies, including solar cells, photoelectrocatalysis, and photocatalysis. It has been reported that amorphous phases can improve both efficiency and stability in these applications. While these phenomena are well established, their mechanisms have long remained unclear. This review first introduces the general background of amorphous inorganic semiconductor properties and synthesis. Then, the recent successes and current challenges of amorphous inorganic semiconductor-based materials for applications in solar cells, photoelectrocatalysis, and photocatalysis are addressed. In particular, we discuss the mechanisms behind the remarkable performances of amorphous inorganic semiconductors in these fields. Finally, we provide insightful perspectives into further developments for applications of amorphous inorganic semiconductors.

Light-Induced Formation of MoOxSy Clusters on CdS Nanorods as Cocatalyst for Enhanced Hydrogen Evolution

Metal and metal-oxide particles are commonly photodeposited on photocatalysts by reduction and oxidation reactions, respectively, consuming charges that are generated under illumination. This study reveals that amorphous MoO_xS_y clusters can be easily photodeposited at the tips of CdS nanorods (NRs) by in situ photodeposition for the first time. The as-prepared MoO_xS_y-decorated CdS samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP) to determine the composition and the possible formation pathways of the amorphous MoO_xS_y clusters. The MoO_xS_y-tipped CdS samples exhibited better hydrogen evolution performance than pure CdS under visible-light illumination. The enhanced activity is attributed to the formation of intimate interfacial contact between CdS and the amorphous MoO_xS_y clusters, which facilitates the charge separation and transfer. Through time-resolved photoluminescence (TRPL) measurements, it was clearly observed that all MoO_xS_y-decorated CdS samples with different loadings of MoO_xS_y showed a faster PL decay when compared to pure CdS, resulting from the effective trapping of photogenerated electrons by the MoO_xS_y clusters. Kelvin probe force microscopy (KPFM) was further used to study the surface potentials of pure CdS NRs and MoO_xS_y-decorated CdS NRs. A higher surface potential on MoO_xS_y-decorated CdS NRs was observed in the dark, indicating that the loading of MoO_xS_y resulted in a lower surface work function compared to pure CdS NRs. This contributed to the effective electron trapping and separation, which was also reflected by the increased photoelectrochemical response. Thus, this study demonstrates the design and facile synthesis of MoO_xS_y-tipped CdS NRs photocatalysts for efficient solar hydrogen production.

Highly enhanced photocatalytic H2 evolution of Cu2O microcube by coupling with TiO2 nanoparticles

A Cu₂O/TiO₂ p-n heterojunction composite was created via a facile, controllable, one-pot hydrothermal method based on cubic Cu₂O and TiO₂ nanoparticles in the presence of dioctyl sulfosuccinate sodium salt (AOT) surfactant. The TiO₂ nanoparticles with an average edge length of ∼10.1 nm were uniformly distributed on the crystal surface of a Cu₂O cube {100}. The photocatalytic performance of the composite was effectively tuned by controlling the amount of TiO₂. The Cu₂O/TiO₂ (60 wt%, labeled as CT-60) exhibits the highest enhanced photocatalytic activity in hydrogen production with H₂ evolution of 3002.5 μmol g^-1. The yield remained around 92.6% after three cycles. Hydrogen production of the CT-60 is 103 and 8.5 fold higher than the cubic Cu₂O and TiO₂ nanoparticles, respectively. The improvement in photocatalytic performance could be attributed to the formation of p-n heterojunction. Furthermore, the interface effect of Cu₂O and TiO₂ caused a broader absorbance in the visible-light region and the lower recombination of photogenerated electron-hole pairs. It is believed that the Cu₂O/TiO₂ p-n heterojunction composites could provide an alternative method to design highly efficient photocatalysts for solar energy.

Amorphous TiO2 nanostructures: synthesis, fundamental properties and photocatalytic applications

In this review, we mainly highlight the advances made in the development of amorphous TiO₂ nanostructures for photocatalysts. Some perspectives on the challenges and new direction are also discussed.

Copper–nickel embedded into a nitrogen-doped carbon octahedron as an effective bifunctional electrocatalyst

The CuNi-NC serves as an efficient bifunctional catalyst for HER and OER, in which the role of Ni is investigated in detail.

Enhanced visible-light photocatalytic degradation by Mn3O4/CeO2 heterojunction: a Z-scheme system photocatalyst

A novel 1-D Mn₃O₄/CeO₂ heterojunction exhibited enhanced photocatalytic degradation via a Z-scheme system.