Heterojunction electrodes were fabricated by layer-by-layer deposition of WO 3 and BiVO 4 on a conducting glass, and investigated for photoelectrochemical water oxidation under simulated solar light. The electrode with the optimal composition of four layers of WO 3 covered by a single layer of BiVO 4 showed enhanced photoactivity by 74% relative to bare WO 3 and 730% relative to bare BiVO 4 .According to the flat band potential and optical band gap measurements, both semiconductors can absorb visible light and have band edge positions that allow the transfer of photoelectrons from BiVO 4 to WO 3 . The electrochemical impedance spectroscopy revealed poor charge transfer characteristics of BiVO 4 , which accounts for the low photoactivity of bare BiVO 4 . The measurements of the incident photon-to-current conversion efficiency spectra showed that the heterojunction electrode utilized effectively light up to 540 nm covering absorption by both WO 3 and BiVO 4 layers. Thus, in heterojunction electrodes, the photogenerated electrons in BiVO 4 are transferred to WO 3 layers with good charge transport characteristics and contribute to the high photoactivity. They combine merits of the two semiconductors, i.e. excellent charge transport characteristics of WO 3 and good light absorption capability of BiVO 4 for enhanced photoactivity.

To investigate the formation of one-dimensional CdS nanowires, we synthesized them by a solvothermal method in ethylenediamine as a single solvent at different temperatures and times. The sample synthesized at 160 °C for 72 h had an average diameter of ca. 50 nm and a length of ca. 3−4 μm and hexagonal phase with high crystallinity. It was revealed that the formation of CdS nanowires followed three-step processes during the solvothermal synthesis; the seed formation process yielded nanosheets emanating from a mirosphere followed by the nanorod formation and growth of nanorods to nanowires. The CdS nanowires with higher crystallinity showed a higher rate of photocatalytic hydrogen production from water containing 0.1 M Na2S and 0.0 2M Na2SO3 as sacrificial reagents under visible light irradiation (λ ≥ 420 nm). A high and stable photocurrent generation was also observed from the CdS nanowire film under visible light.

The visible-light-induced water oxidation ability of metal-ion-doped BiVO(4) was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO(4); Mo had the highest improvement by a factor of about six. Thus, BiVO(4) and W- or Mo-doped (2 atom %) BiVO(4) photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal-organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm(-2)) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (J(PH)) of about 2.38 mA cm(-2) was achieved for Mo doping followed by W doping (J(PH) ≈ 1.98 mA cm(-2)), whereas undoped BiVO(4) gave a J(PH) value of about 0.42 mA cm(-2). The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO(4) photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott-Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6-2 times higher, and a charge-transfer resistance reduced by 3-4-fold for W- or Mo-doped BiVO(4) relative to undoped BiVO(4). Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO(4) photoanodes (undoped

A picoliter solution dispenser was used to fabricate various n-type BiVO4 based photocatalyst arrays having different compositions and a scanning electrochemical microscopy (SECM) technique modified by replacing a normal ultramicroelectrode with an optical fiber was used for fast screening of the effective photocatalysts for Na2SO3 (as a sacrificial reductant) and water oxidation. Bi/V/W oxide with a ratio of 4.5:5:0.5 showed ∼4.6× higher photocurrent than Bi/V oxide without W and this result was confirmed with bulk film studies. Preliminary characterization (XRD, XPS, and EIS) was also performed for these catalysts. This material was tested for photoelectrochemical water oxidation with a Pt ring optical fiber to detect the product (O2) of photoelectrochemical oxidation reaction.

The electrocatalytic properties of individual single Pt nanoparticles (NPs) can be studied electrochemically by measuring the current−time (i−t) responses during single NP collisions with a noncatalytic ultramicroelectrode (UME). The Pt NPs are capped with citrate ions or a self-assembled monolayer (SAM) of alkane thiols terminated with carboxylic acid that affect the observed i−t responses. By varying the length of the SAMs or the composition of a mixed monolayer, we have studied the effect of adsorbed molecules on the catalytic activity of Pt NPs at the single particle level through electrocatalytic amplification of single NP collisions. Collisions of single NPs were triggered and recorded as individual current steps whose amplitude represents the reactivity of single Pt NPs for the reaction of interest, here hydrazine oxidation, at a given electrode potential. The catalytic properties of Pt NPs are dependent not only on the nature of the interaction between the adsorbed monolayer and the catalytic NP surface, but also on the rate of electron transfer through the SAMs, governed by their length.