Unbiased solar energy storage: Photoelectrochemical redox flow battery

Electricity from renewable energy sources is craving for efficient storage technologies, in particularsolar industry, to enable practical small-scale solutions for residential and offices use. The beststationary technology is probably the redox flow batteries. This article proposes the directconversion of sunlight into electrochemical energy stored in a redox flow battery. A photoelectrochemicalcell is used to charge a vanadium redox flow cell (CdS(s)|V3+, VO2+||V3+, V2+|CarbonFelt(s), E0=0.6 VNHE). A CdS thin film photoelectrode is prepared to directly charge the cell, pairsV3+/VO2+. CdS photoanode exhibits competitive photocurrents, when compared to other photoelectrochemicaldevices, and yields enough photovoltage to charge the vanadium battery up to 75%with no external bias. An overlayer of CdSe improves the performance of CdS with current densitiesup to ca. 1.4 mA cm2. Finally, a tandem configuration is tested using a dye-sensitized solar cell anda CdS photoanoade creating 1.3 V of photovoltage. This tandem arrangement proves to chargeconventional all vanadium redox cell (DSC/CdS(s)|VO2+, VO2+||V3+, V2+|Carbon Felt(s), E0=1.2 VNHE)without external bias

Unbiased, complete solar charging of a neutral flow battery by a single Si photocathode

Solar redox flow batteries have attracted attention as a possible integrated technology for simultaneous conversion and storage of solar energy. In this work, we review current efforts to design aqueous solar flow batteries in terms of battery electrolyte capacity, solar conversion efficiency and depth of solar charge. From a materials cost and design perspective, a simple, cost-efficient, aqueous solar redox flow battery will most likely incorporate only one semiconductor, and we demonstrate here a system where a single photocathode is accurately matched to the redox couples to allow for a complete solar charge. The single TiO(2) protected Si photocathode with a catalytic Pt layer can fully solar charge a neutral TEMPO-sulfate/ferricyanide battery with a cell voltage of 0.35 V. An unbiased solar conversion efficiency of 1.6% is obtained and this system represents a new strategy in solar RFBs where a single silicon photocathode is paired with energetically suitable redox couples to build an integrated solar energy conversion and storage device with full realization of the energy storage capacity

Quinone-mediated extracellular electron transfer processes in ex situ biomethanation reactors

Redox mediators are used in a wide diversity of systems including biological ones. We investigated the effect of adding an artificial quinone (2,7-AQDS) as external redox molecule to an anaerobic digester system dominated by hydrogenotrophic methanogens. When oxidized AQDS was present, the methanogens diverted electrons from H2 to reduce AQDS instead of CO2. The AQDS reduction process was accompanied by a temporary CH4 inhibition, which was re-established several days after the full reduction of AQDS to AH2QDS. The presence of AQDS furthermore resulted in a community shift from Methanobacterium as the dominant methanogen to a more diverse community of methanogens. Protein expression profiles showed a shift in cofactor preference of the adapted community, as a potential response mechanism to AQDS inhibition. AH2QDS was only used as electron donor to a limited extent. Stable isotope incorporation experiments here indicated that the acetogen Acetoanaerobium used AH2QDS to reduce CO2 into acetate.</p

Thermoelectric Properties of YMn4+xAl8-x, -2 ≤ x ≤ 2.5

Seven samples within the series YMn 4+x Al 8 - x (-2.0 ≤ x ≤ 2.5) were synthesized using direct reaction of the elements. The thermoelectric properties of the samples were characterized by measurements of resistivity, thermal conductivity and thermopower. According to transport measurements, slight Mn-deficiency influences the electronic conductivity of the YMn 4+x Al 8 - x system, implying that the electronic structure is marginal to the metal-semiconductor boundary. Furthermore, the ZT values of the samples prepared in this study were low. Experimental results indicated that structurally ordered YMn 4 Al 8 shows metallic conductivity, whereas off-stoichiometric compounds displayed semiconductor-like behavior, at low temperatures. \ua9 2008 Elsevier B.V. All rights reserved

Thermoelectric Properties of YMn4+xAl8-x, -2 ≤ x ≤ 2.5

Seven samples within the series YMn 4+x Al 8 - x (-2.0 ≤ x ≤ 2.5) were synthesized using direct reaction of the elements. The thermoelectric properties of the samples were characterized by measurements of resistivity, thermal conductivity and thermopower. According to transport measurements, slight Mn-deficiency influences the electronic conductivity of the YMn 4+x Al 8 - x system, implying that the electronic structure is marginal to the metal-semiconductor boundary. Furthermore, the ZT values of the samples prepared in this study were low. Experimental results indicated that structurally ordered YMn 4 Al 8 shows metallic conductivity, whereas off-stoichiometric compounds displayed semiconductor-like behavior, at low temperatures. \ua9 2008 Elsevier B.V. All rights reserved

The 3-Omega Method for the Measurement of Fouling Thickness, the Liquid Flow Rate, and Surface Contact

The 3-omega method is conventionally used for the measurement of thermal conductivity in solid samples. The present work includes the experimental characterization and proof-of-concept measurements of sensor concepts, based on the 3-omega method. It is shown that this method can be used to measure fouling layers with a thickness of 10 to 400 μm, to conduct the measurement of flow rates with a high precision, and finally, as a simple on-off contact sensor with a fast response time

Steady State and Dynamic Response of Voltage-Operated Membrane Gates

An electrochemical flow cell with Nafion 212, aqueous LiI/I 2 redox solution, and carbon paper electrode was operated as an electro-osmotic gate based on the Electrokinetic Energy Conversion (EKEC) principle. The gate was operated in different modes. (i) In normal DC pump operation it is shown to follow the predictions from the phenomenological transport equations. (ii) Furthermore, it was also demonstrated to operate as a normally open, voltage-gated valve for microfluidic purposes. For both pump and valve operations low energy requirements (mW range) were estimated for precise control of small flows ( μ L range). (iii) Finally, the dynamic response of the pump was investigated by using alternating currents at a range of different frequencies