Engineered Hematite Mesoporous Single Crystals Drive Drastic Enhancement in Solar Water Splitting.

Mesoporous single crystals (MSCs) rendering highly accessible surface area and long-range electron conductivity are extremely significant in many fields, including catalyst, solar fuel, and electrical energy storage technologies. Hematite semiconductor, whose performance has been crucially limited by its pristine poor charge separation efficiency in solar water splitting, should benefit from this strategy. Despite successful synthesis of many metal oxide MSCs, the fabrication of hematite MSCs remains to be a great challenge due to its quite slow hydrolysis rate in water. Herein, for the first time, we have developed a synthetic strategy to prepare hematite MSCs and systematically investigated their growth mechanism. The electrode fabricated with these crystals is able to achieve a photocurrent density of 0.61 mA/cm(2) at 1.23 V vs RHE under AM 1.5G simulated sunlight, which is 20 times higher than that of electrodes made of solid single crystals. The enhancement is ascribed to the superior light absorption and enhanced charges separation. Our results demonstrate the advantage of incorporation of nanopores into the large-sized hematite single crystals and provide a valuable insight for the development of high performance photoelectrodes in PEC application.

Fluorine-doped porous single-crystal rutile TiO2 nanorods for enhancing photoelectrochemical water splitting.

Fluorine-doped hierarchical porous single-crystal rutile TiO(2) nanorods have been synthesized through a silica template method, in which F(-) ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at -0.33 V vs. Ag/AgCl) under 100 mW cm(-2) of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO(2) single crystals.

Operando NMR spectroscopic analysis of proton transfer in heterogeneous photocatalytic reactions.

Proton transfer (PT) processes in solid-liquid phases play central roles throughout chemistry, biology and materials science. Identification of PT routes deep into the realistic catalytic process is experimentally challenging, thus leaving a gap in our understanding. Here we demonstrate an approach using operando nuclear magnetic resonance (NMR) spectroscopy that allows to quantitatively describe the complex species dynamics of generated H2/HD gases and liquid intermediates in pmol resolution during photocatalytic hydrogen evolution reaction (HER). In this system, the effective protons for HER are mainly from H2O, and CH3OH evidently serves as an outstanding sacrificial agent reacting with holes, further supported by our density functional theory calculations. This results rule out controversy about the complicated proton sources for HER. The operando NMR method provides a direct molecular-level insight with the methodology offering exciting possibilities for the quantitative studies of mechanisms of proton-involved catalytic reactions in solid-liquid phases.

Rational screening low-cost counter electrodes for dye-sensitized solar cells.

Dye-sensitized solar cells have attracted intense research attention owing to their ease of fabrication, cost-effectiveness and high efficiency in converting solar energy. Noble platinum is generally used as catalytic counter electrode for redox mediators in electrolyte solution. Unfortunately, platinum is expensive and non-sustainable for long-term applications. Therefore, researchers are facing with the challenge of developing low-cost and earth-abundant alternatives. So far, rational screening of non-platinum counter electrodes has been hamstrung by the lack of understanding about the electrocatalytic process of redox mediators on various counter electrodes. Here, using first-principle quantum chemical calculations, we studied the electrocatalytic process of redox mediators and predicted electrocatalytic activity of potential semiconductor counter electrodes. On the basis of theoretical predictions, we successfully used rust (α-Fe2O3) as a new counter electrode catalyst, which demonstrates promising electrocatalytic activity towards triiodide reduction at a rate comparable to platinum.

Inorganic photocatalysts for overall water splitting.

Photocatalytic water splitting using semiconductor photocatalysts has been considered as a "green" process for converting solar energy into hydrogen. The pioneering work on electrochemical photolysis of water at TiO(2) electrode, reported by Fujishima and Honda in 1972, ushered in the area of solar fuel. As the real ultimate solution for solar fuel-generation, overall water splitting has attracted interest from researchers for some time, and a variety of inorganic photocatalysts have been developed to meet the challenge of this dream reaction. To date, high-efficiency hydrogen production from pure water without the assistance of sacrificial reagents remains an open challenge. In this Focus Review, we aim to provide a whole picture of overall water splitting and give an outlook for future research.