Hetero-type dual photoanodes for unbiased solar water splitting with extended light harvesting

Metal oxide semiconductors are promising photoelectrode materials for solar water splitting due to their robustness in aqueous solutions and low cost. Yet, their solar-to-hydrogen conversion efficiencies are still not high enough for practical applications. Here we present a strategy to enhance the efficiency of metal oxides, hetero-type dual photoelectrodes, in which two photoanodes of different bandgaps are connected in parallel for extended light harvesting. Thus, a photoelectrochemical device made of modified BiVO4 and alpha-Fe2O3 as dual photoanodes utilizes visible light up to 610nm for water splitting, and shows stable photocurrents of 7.0 +/- 0.2 mA cm(-2) at 1.23 V-RHE under 1 sun irradiation. A tandem cell composed with the dual photoanodes-silicon solar cell demonstrates unbiased water splitting efficiency of 7.7%. These results and concept represent a significant step forward en route to the goal of >10% efficiency required for practical solar hydrogen production.ope

A simple method for producing mesoporous anatase TiO2 nanocrystals with elevated photovoltaic performance

Mesoporous anatase TiO2 nanocrystals with high crystallinity and large surface area were synthesized by an easy one-step method, combining hydrolysis and alcothemal processes, without the use of a templating agent. The photovoltaic performance of photoanodes for dye-sensitized solar cell under 1 sun (AM 1.5G) illumination gave a solar conversion efficiency as high as 6.06%, an enhancement of similar to 20% with respect to that of a reference photoanode made of a commercial TiO2 (Degussa, P25) powder. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X112727sciescopu

Photocatalytic and Photoelectrochemical Water Oxidation over Metal-Doped Monoclinic BiVO4 Photoanodes

The visible-light-induced water oxidation ability of metal-ion-doped BiVO4 was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO4; Mo had the highest improvement by a factor of about six. Thus, BiVO4 and W- or Mo-doped (2 atom?%) BiVO4 photoanodes about 1 mu m thick were fabricated onto transparent conducting substrate by a metalorganic 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 (JPH) of about 2.38 mA?cm-2 was achieved for Mo doping followed by W doping (JPH approximate to 1.98 mA?cm-2), whereas undoped BiVO4 gave a JPH value of about 0.42 mA?cm-2. The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO4 photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40?% respectively. Electrochemical impedance spectroscopy and MottSchottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.62 times higher, and a charge-transfer resistance reduced by 34-fold for W- or Mo-doped BiVO4 relative to undoped BiVO4. 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 BiVO4 photoanodes (undoped<W doped<Mo doped) was in accordance with the results from electrochemical impedance spectroscopy, MottSchottky analysis, and theoretical electronic structural calculations. Thus, Mo or W doping enhanced the photocatalytic and photoelectrochemical water oxidation activity of monoclinic BiVO4 by drastically reducing its charge-transfer resistance and thereby minimizing photoexcited electronhole pair recombination.X11147119sciescopu

TLBO algorithm optimized fractional-order PID controller for AGC of interconnected power system

The present study focuses on the problem of automatic generation control (AGC) by employing the design of fractional-order proportional–integral– derivative controller (FOPID). A hydrothermal power system with governor dead band (GDB) and generation rate constraint (GRC) is considered for investigation. FOPID controller optimal values are obtained by using teacher learning-based optimization (TLBO) technique, and the employed objective function is integral time-multiplied absolute error (ITAE). The supremacy of the proposed controller is also shown by comparing with PID controller. Further, the performance of the system is analyzed by varying parameter values of the system. From the simulation results, it reveals that TLBO optimized FOPID controller minimizes the errors in frequency of the control areas and tie-line power effectively