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

Hydrogen has been touted as an energy carrier of the future because it combines with oxygen to produce only water with no greenhouse gases or other pollutants. For hydrogen to play the role, it must be produced in a sustainable manner from a renewable energy source, such as solar energy. [1] Unlike the electricity produced from the most common photovoltaic cells, hydrogen could store the solar energy in the form of chemical energy. One of the most attractive solar energy conversion reactions is the photoelectrochemical (PEC) or photocatalytic water splitting directly to H 2 and O 2 . Since its initial demonstration by Fujishima and Honda with a TiO 2 electrode under ultraviolet light, [2] there has been steady progress in this field in search of semiconductor photocatalytic electrode materials that work under visible light irradiation for ample solar light absorption. However, the photocatalysts with high efficiency, durability, and economic feasibility are still elusive. [3,4] Scheelite-monoclinic BiVO 4 (mBiVO 4 ) is a well-known photocatalyst, which absorbs visible light owing to a suitable band-gap energy (E g % 2.4 eV). [5,6] It is also nontoxic and chemically stable in aqueous solution under irradiation. However, pristine mBiVO 4 usually shows a low photocatalytic activity owing to poor charge-transport characteristics [7] and the weak surface adsorption properties. [8] Numerous attempts have been made to improve the photocatalytic activity of BiVO 4 , including heterojunction structure formation, [7,9,10] loading co-catalysts, [11][12][13] and impurity doping. [8,14,15] Impurity doping, that is, the addition of a small percentage of foreign atoms in the regular crystal lattice of semiconductors, produces dramatic changes in their electrical properties by increasing their electron or hole densities. In photocatalysis by BiVO 4 , for example, doping with molybdenum to replace a small fraction of vanadium was found to improve the photocatalytic activity for water oxidation. [8,14,15] Phosphorus is a typical dopant for silicon or germanium to make it an n-type semiconductor. However, it has been rarely used as dopant for semiconductor photocatalysts. This is rather surprising because other non-metallic elements, such as N, C, and S, have been widely used as anionic dopants for photocatalysts to reduce their band-gap energies. [16] In the present work, for the first time we doped phosphorous into the vanadium sites in the host lattice of BiVO 4 , replacing some of the VO 4 oxoanions in BiVO 4 with PO 4 oxoanions. Oxoanion doping into the photocatalyst is to the best of our knowledge also a new concept. Herein we report effects of PO 4 oxoanion doping on the photoelectrochemical or photocatalytic behavior of mBiVO 4 under visiblelight illumination. The PO 4 oxoanion doping did not bring about significant changes in the optical absorption behavior and crystal structure of mBiVO 4 . When an appropriate amount PO 4 oxoanion was doped, however, the activity of photoelectrochemical water oxidation increased very sign...

We have studied the effect of an external direct current (DC) electric field ( approximately 1 kV/mm) on the rheological properties of colloidal suspensions consisting of aggregates of laponite particles in a silicone oil. Microscopy observations show that, under application of an electric field greater than a triggering electric field Ec approximately 0.6 kV/mm, laponite aggregates assemble into chain- and/or columnlike structures in the oil. Without an applied electric field, the steady-state shear behavior of such suspensions is Newtonian-like. Under application of an electric field larger than Ec, it changes dramatically as a result of the changes in the microstructure: a significant yield stress is measured, and under continuous shear the fluid is shear-thinning. The rheological properties, in particular the dynamic and static shear stress, were studied as a function of particle volume fraction for various strengths (including null) of the applied electric field. The flow curves at constant shear rate can be scaled with respect to both the particle fraction and electric field strength onto a master curve. This scaling is consistent with simple scaling arguments. The shape of the master curve accounts for the system's complexity; it approaches a standard power-law model at high Mason numbers. Both dynamic and static yield stresses are observed to depend on the particle fraction Phi and electric field E as PhibetaEalpha, with alpha approximately 1.85 and beta approximately 1 and 1.70 for the dynamic and static yield stresses, respectively. The yield stress was also determined as the critical stress at which there occurs a bifurcation in the rheological behavior of suspensions that are submitted to a constant shear stress; a scaling law with alpha approximately 1.84 and beta approximately 1.70 was obtained. The effectiveness of the latter technique confirms that such electrorheological (ER) fluids can be studied in the framework of thixotropic fluids. The method is very reproducible; we suggest that it could be used routinely for studying ER fluids. The measured overall yield stress behavior of the suspensions may be explained in terms of standard conduction models for electrorheological systems. Interesting prospects include using such systems for guided self-assembly of clay nanoparticles.