Water Reduction Photocathodes Based on Ru Complex Dyes Covered with a Conjugated Polymer Nanosheet

Water-splitting dye-sensitized photoelectrochemical cells are promising devices for resolving energy and environmental problems by producing H-2, a clean energy source, from water and sunlight. However, their performance is still limited because of dye desorption from the electrode and their weak light-absorption efficiency. In this study, we fabricated two water-reducing photocathodes, NiO vertical bar RuCP/BQPy and NiO vertical bar RuCP-Zr-RuP/BQPy, by combining the layer-by-layer formation of mono(RuCP) and bi- (RuCP and RuP with Zr4+ cations) layer molecular films of Ru(II) dyes, respectively, on a p-type NiO substrate with the chemical vapor deposition of the nanosheet catalyst based on the BQPy organic polymer comprising benzoquinone and pyrrole moieties. These photocathodes produced H-2 under visible light irradiation and a small electrical bias in a 0.1 M Na2SO4 aqueous solution (lambda > 420 nm, 65 mW cm(-2), E = -0.254 V versus normal hydrogen electrode, and pH 3). Both the photocurrent value and amount of H-2 produced by double-dye-layered NiO vertical bar RuCP-Zr-RuP/BQPy were smaller than those of NiO vertical bar RuCP/BQPy, probably because of the energy transfer inactivation between the Ru(II) dyes, which competes with the reductive quenching (i.e., electron injection) by NiO. Ru(II) dye desorption from the NiO vertical bar RuCP/BQPy photocathode was significantly reduced to approximately a third of that of NiO vertical bar RuCP, indicating that the deposited BQPy polymer improved the durability of the photocathode. The deposition of the BQPy polymer can be easily performed under mild conditions (60 degrees C in air); therefore, this technique shows great potential application for the construction of various types of dye-sensitized water-reducing photocathodes

Monolayered Nanodots of Transition Metal Oxides

Monolayered nanodots of titanium, tungsten, and manganese oxides were obtained by exfoliation of the nanocrystals through aqueous solution processes at room temperature. The precursor nanocrystals of the layered compounds, such as sodium titanate (Na_0.80Ti_1.80□_0.2O₄·<i>x</i>H₂O, □: vacancy (<i>x</i> < 1.17)), cesium tungstate (Cs₄W₁₁O₃₅·<i>y</i>H₂O (<i>y</i> < 10.5)), and sodium manganate (Na_0.44MnO₂·<i>z</i>H₂O (<i>z</i> < 0.85)), were synthesized in an aqueous solution. These nanocrystals of the layered compounds were delaminated into the monolayered nanodots through introduction of a bulky organic cation in the interlayer space. The resultant monolayered nanodots of the titanate and tungstate 2–5 nm in lateral size showed a remarkable blueshift of the bandgap energies. The calculation studies supported the blueshifts of the bandgap energies. The results suggest that syntheses of monolayered nanodots can expand the tuning range of the properties based on size effect. The present approaches for generation of ultrathin tiny objects can be applied to a variety of nanomaterials