Scalable and sustainable solar hydrogen production through photocatalytic water splitting requires highly active and stable earth-abundant co-catalysts to replace expensive and rare platinum. Here we employ density functional theory calculations to direct atomic-level exploration, design and fabrication of a MXene material, Ti3C2 nanoparticles, as a highly efficient co-catalyst. Ti3C2 nanoparticles are rationally integrated with cadmium sulfide via a hydrothermal strategy to induce a super high visible-light photocatalytic hydrogen production activity of 14,342 μmol h−1 g−1 and an apparent quantum efficiency of 40.1% at 420 nm. This high performance arises from the favourable Fermi level position, electrical conductivity and hydrogen evolution capacity of Ti3C2 nanoparticles. Furthermore, Ti3C2 nanoparticles also serve as an efficient co-catalyst on ZnS or ZnxCd1−xS. This work demonstrates the potential of earth-abundant MXene family materials to construct numerous high performance and low-cost photocatalysts/photoelectrodes.

The design and synthesis of metal oxide nanomaterials is one of the key steps for achieving highly efficient energy conversion and storage on an industrial scale. Solution combustion synthesis (SCS) is a time- and energy-saving method as compared with other routes, especially for the preparation of complex oxides which can be easily adapted for scale-up applications. This review summarizes the synthesis of various metal oxide nanomaterials and their applications for energy conversion and storage, including lithium-ion batteries, supercapacitors, hydrogen and methane production, fuel cells and solar cells. In particular, some novel concepts such as reverse support combustion, self-combustion of ionic liquids, and creation of oxygen vacancies are presented. SCS has some unique advantages such as its capability for in situ doping of oxides and construction of heterojunctions. The well-developed porosity and large specific surface area caused by gas evolution during the combustion process endow the resulting materials with exceptional properties. The relationship between the structural properties of the metal oxides studied and their performance is discussed. Finally, the conclusions and perspectives are briefly presented.

Piezocatalysis,converting mechanical vibration into chemical energy,h as emerged as ap romising candidate for water-splitting technology.H owever,t he efficiency of the hydrogen production is quite limited. We herein report welldefined 10 nm BaTiO 3 nanoparticles (NPs) characterized by al arge electro-mechanical coefficient which induces ah igh piezoelectric effect. Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM) and scanning probe microscopy(SPM) suggests that piezoelectric BaTiO 3 NPs displayac oexistence of multiple phases with lowe nergy barriers and polarization anisotropy which results in ahigh electro-mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropyf acilitates polarization rotation. Employing the high piezoelectric properties of BaTiO 3 NPs,w e demonstrate an overall water-splitting process with the highest hydrogen production efficiency hitherto reported, with aH 2 production rate of 655 mmol g À1 h À1 ,whichcould rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting.

As emerging noble metal-free co-catalysts, transition metal phosphides have been employed to improve photocatalytic H2 production activity. Herein, the metallicity of CoP, as a representative phosphide, and the Schottky effect between CoP and g-C3N4 are confirmed via theoretical calculations. Then, a 2D/2D structure is designed to enlarge the Schottky effect between the interfaces, for which the apparent quantum efficiency of the photocatalytic H2 evolution is 2.1 times that of corresponding 0D/2D heterojunctions. The morphology, microstructure, chemical composition, and physical nature of pristine CoP, g-C3N4, and the composites are characterized in order to investigate the dynamic behavior of photo-induced charge carriers between CoP and g-C3N4. Based on the measurements, it is proposed that the efficient electron collecting effect of CoP can be attributed to the superior interfacial contact and Schottky junction between the CoP and g-C3N4 interfaces. Furthermore, the excellent electrical conductivity and low overpotential of CoP make water reduction easier. This work demonstrates that the construction of a 2D/2D structure based on a suitable Fermi level is crucial for enhancing the Schottky effect of transition metal phosphides.

Heterostructured BiOBr/Bi24O31Br10 nanocomposites with surface oxygen vacancies are constructed by a facile in situ route of one-step self-combustion of ionic liquids. The compositions can be easily controlled by simply adjusting the fuel ratio of urea and 2-bromoethylamine hydrobromide (BTH). BTH serves not only as a fuel, but also as a complexing agent for ionic liquids and a reactant to supply the Br element. The heterojunctions show remarkable adsorptive ability for both the cationic dye of rhodamine B (RhB) and the anionic dye of methylene orange (MO) at high concentrations, which is attributed to the abundant surface oxygen vacancies. The sample containing 75.2% BiOBr and 24.8% Bi24O31Br10 exhibits the highest photocatalytic activity. Its reaction rate constant is 4.0 and 9.0 times that of pure BiOBr in degrading 50 mg L(-1) of RhB and 30 mg L(-1) of MO under visible-light (λ > 400 nm) irradiation, respectively, which is attributed to the narrow band gap and highly efficient transfer efficiency of charge carriers. Different photocatalytic reaction processes and mechanisms over pure BiOBr and heterojunctions are proposed.

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Piezocatalysis,converting mechanical vibration into chemical energy,h as emerged as ap romising candidate for water-splitting technology.H owever,t he efficiency of the hydrogen production is quite limited. We herein report welldefined 10 nm BaTiO 3 nanoparticles (NPs) characterized by al arge electro-mechanical coefficient which induces ah igh piezoelectric effect. Atomic-resolution high angle annular dark field scanning transmission electron microscopy(HAADF-STEM) and scanning probe microscopy(SPM) suggests that piezoelectric BaTiO 3 NPs displayac oexistence of multiple phases with lowe nergy barriers and polarization anisotropy which results in ahigh electro-mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropyf acilitates polarization rotation. Employing the high piezoelectric properties of BaTiO 3 NPs,w e demonstrate an overall water-splitting process with the highest hydrogen production efficiency hitherto reported, with aH 2 production rate of 655 mmol g À1 h À1 ,whichcould rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting.