Enhanced Photoelectrochemical Water Splitting through Bismuth Vanadate with a Photon Upconversion Luminescent Reflector

As the performance of photoanodes for solar water splitting steadily improves, the extension of the absorption wavelength in the photoanodes is highly necessary to substantially improve the water splitting. We use a luminescent back reflector (LBR) capable of photon upconversion (UC) to improve the light harvesting capabilities of Mo:BiVO₄ photoelectrodes. The LBR is prepared by dispersing the organic dye pair meso‐tetraphenyltetrabenzoporphine palladium and perylene capable of triplet–triplet annhilation‐based UC in a polymer film. The LBR converts the wavelengths of 600–650 nm corresponding to the sub‐band gap of Mo:BiVO₄ and the wavelengths of 350–450 nm that are not sufficiently absorbed in Mo:BiVO₄ to a wavelength that can be absorbed by a Mo:BiVO₄ photoelectrode. The LBR improves the water splitting reaction of Mo:BiVO₄ photoelectrodes by 17 %, and consequently, the Mo:BiVO₄/LBR exhibits a photocurrent density of 5.25 mA cm^?2 at 1.23 V versus the reversible hydrogen electrode. The Mo:BiVO₄/LBR exhibits hydrogen/oxygen evolution corresponding to the increased photocurrent density and long‐term operational stability for the water splitting reaction.     

Artificial Mn4Ca Clusters with Exchangeable Solvent Molecules Mimicking the Oxygen‐Evolving Center in Photosynthesis

The natural Mn₄Ca cluster in photosystem II serves as a blueprint to develop artificial water‐splitting catalysts for the generation of solar fuel in artificial photosynthesis. Although significant advances have recently been achieved, it remains a great challenge to prepare robust artificial Mn₄Ca clusters that precisely mimic the structure and function of the biological catalyst. Herein, we report the isolation and structural characterization of two Mn₄CaO₄ complexes with polar solvent molecules, acetonitrile or N,N‐dimethylformamide, which closely mimics the two water molecules on the calcium ion, as well as the oxidation states of the four manganese ions and the main geometric structure of the natural Mn₄Ca cluster. These new artificial Mn₄Ca complexes provide important chemical clues to understand the structure and mechanism of the biological system.     

Boosting Visible‐Light‐Driven Photocatalytic Hydrogen Evolution with an Integrated Nickel Phosphide–Carbon Nitride System

Solar light harvesting by photocatalytic H₂ evolution from water could solve the problem of greenhouse gas emission from fossil fuels with alternative clean energy. However, the development of more efficient and robust catalytic systems remains a great challenge for the technological use on a large scale. Here we report the synthesis of a sol–gel prepared mesoporous graphitic carbon nitride (sg‐CN) combined with nickel phosphide (Ni₂P) which acts as a superior co‐catalyst for efficient photocatalytic H₂ evolution by visible light. This integrated system shows a much higher catalytic activity than the physical mixture of Ni₂P and sg‐CN or metallic nickel on sg‐CN under similar conditions. Time‐resolved photoluminescence and electron paramagnetic resonance (EPR) spectroscopic studies revealed that the enhanced carrier transfer at the Ni₂P–sg‐CN heterojunction is the prime source for improved activity.     

Freeing the Polarons to Facilitate Charge Transport in BiVO4 from Oxygen Vacancies with an Oxidative 2D Precursor

The BiVO₄ photoelectrochemical (PEC) electrode in tandem with a photovoltaic (PV) cell has shown great potential to become a compact and cost‐efficient device for solar hydrogen generation. However, the PEC part is still facing problems such as the poor charge transport efficiency owing to the drag of oxygen vacancy bound polarons. In the present work, to effectively suppress oxygen vacancy formation, a new route has been developed to synthesize BiVO₄ photoanodes by using a highly oxidative two‐dimensional (2D) precursor, bismuth oxyiodate (BiOIO₃), as an internal oxidant. With the reduced defects, namely the oxygen vacancies, the bound polarons were released, enabling a fast charge transport inside BiVO₄ and doubling the performance in tandem devices based on the oxygen vacancy eliminated BiVO₄. This work is a new avenue for elaborately designing the precursor and breaking the limitation of charge transport for highly efficient PEC‐PV solar fuel devices.     

Constructing SrTiO3–TiO2 Heterogeneous Hollow Multi‐shelled Structures for Enhanced Solar Water Splitting

Constructing hollow multi‐shelled structures (HoMSs) has a significant effect on promoting light absorption property of catalysts and enhancing their performance in solar energy conversion applications. A facile hydrothermal method is used to design the SrTiO₃?TiO₂ heterogeneous HoMSs by hydrothermal crystallization of SrTiO₃ on the surface of the TiO₂ HoMSs, which will realize a full coverage of SrTiO₃ on the TiO₂ surface and construct the SrTiO₃/TiO₂ junctions. The broccoli‐like SrTiO₃?TiO₂ heterogeneous HoMSs exhibited a fourfold higher overall water splitting performance of 10.6 μmol h^?1 for H₂ production and 5.1 μmol h^?1 for O₂ evolution than that of SrTiO₃ nanoparticles and the apparent quantum efficiency (AQE) of 8.6 % at 365 nm, which can be mainly attributed to 1) HoMS increased the light absorption ability of the constructed photocatalysts and 2) the SrTiO₃?TiO₂ junctions boosted the separation efficiency of the photogenerated charge carriers.