Highly efficient water oxidation utilizing visible photons of up to 600 nm is a crucial step in artificial photosynthesis. Here we present a highly active photocatalyst for visible-light-driven water oxidation, consisting of single-crystalline meso- and macroporous LaTiO(2)N (LTON) with a band gap of 2.1 eV, and earth-abundasnt cobalt oxide (CoO(x)) as a cocatalyst. The optimized CoO(x)/LTON had a high quantum efficiency of 27.1 ± 2.6% at 440 nm, which substantially exceeds the values reported for previous particulate photocatalysts with a 600-nm absorption edge.

Oxynitride photocatalysts hold promise for renewable solar hydrogen production via water splitting owing to their intense visible light absorption. Cocatalyst loading is essential for activation of such oxynitride photocatalysts. However, cocatalyst nanoparticles form aggregates and exhibit weak interaction with photocatalysts, which prevents eliciting their intrinsic photocatalytic performance. Here, we demonstrate efficient utilization of photoexcited electrons in a single-crystalline particulate BaTaO2N photocatalyst prepared with the assistance of RbCl flux for H2 evolution reactions via sequential decoration of Pt cocatalyst by impregnation-reduction followed by site-selective photodeposition. The Pt-loaded BaTaO2N photocatalyst evolves H2 over 100 times more efficiently than before, with an apparent quantum yield of 6.8% at the wavelength of 420 nm, from a methanol aqueous solution, and a solar-to-hydrogen energy conversion efficiency of 0.24% in Z-scheme water splitting. Enabling uniform dispersion and intimate contact of cocatalyst nanoparticles on single-crystalline narrow-bandgap particulate photocatalysts is a key to efficient solar-to-chemical energy conversion.

Ta N is a very promising photocatalyst for solar water splitting because of its wide spectrum solar energy utilization up to 600 nm and suitable energy band position straddling the water splitting redox reactions. However, its development has long been impeded by poor compatibility with electrolytes. Herein, we demonstrate a simple sputtering-nitridation process to fabricate high-performance Ta N film photoanodes owing to successful synthesis of the vital TaO precursors. An effective GaN coating strategy is developed to remarkably stabilize Ta N by forming a crystalline nitride-on-nitride structure with an improved nitride/electrolyte interface. A stable, high photocurrent density of 8 mA cm was obtained with a CoPi/GaN/Ta N photoanode at 1.2 V under simulated sunlight, with O and H generated at a Faraday efficiency of unity over 12 h. Our vapor-phase deposition method can be used to fabricate high-performance (oxy)nitrides for practical photoelectrochemical applications.

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As the 600 nm-class photocatalyst, BaTaO 2 N is one of the promising candidates of the perovskite-type oxynitride family for photocatalytic water splitting under visible light. The oxynitrides are routinely synthesized by nitriding corresponding oxide precursors under a high-temperature NH 3 atmosphere, causing an increase in the defect density and a decrease in photocatalytic activity. To improve the photocatalytic activity by reducing the defect density and improving the crystallinity, we here demonstrate an NH 3 -assisted KCl flux growth approach for the direct synthesis of the BaTaO 2 N crystals. The effects of various fluxes, solute concentration, and reaction time and temperature on the phase evolution and morphology transformation of the BaTaO 2 N crystals were systematically investigated. By changing the solute concentration from 10 to 50 mol %, it was found that phase-pure BaTaO 2 N crystals could only be grown with the solute concentrations of ≥ 10 mol % using the KCl flux, and the solute concentration of 10 mol % was solely favorable to directly grow cube-like BaTaO 2 N crystals with an average size of about 125 nm and exposed {100} and {110} faces at 950 °C for 10 h. The time-and temperature-dependent experiments were also performed to postulate the direct growth mechanisms of cube-like BaTaO 2 N submicron crystals. The BaTaO 2 N crystals modified with Pt and CoO x nanoparticles showed a reasonable H 2 and O 2 evolution, respectively, due to a lower defect density and higher crystallinity achieved by an NH 3 -assisted KCl flux method.

Highly dispersed primary Li(Ni1/3Co1/3Mn1/3)O2 crystals, which showed high discharge capacity at a high C-rate, were grown from a Li2MoO4 flux.

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Low charge separation efficiencies are regarded as obstacles that limit the improvement in the photocatalytic performance of BaTaO2N. In this study, we demonstrated that the anisotropic facets ({100} and {110} facets) of BaTaO2N for efficient spatial charge separation were successfully constructed using the one-pot flux-assisted nitridation approach. As a result, the photocatalytic activity for H2 production on BaTaO2N with coexposed {100} and {110} facets was nearly 10-fold over that of BaTaO2N with only {100} facets and that of the conventional irregularly shaped sample. This finding provides an innovative approach to the development of efficient (oxy)­nitride photocatalysts for solar energy conversion.