• Energy Research

AbstractElectricity from renewable energy sources is craving for efficient storage technologies, in particular solar industry, to enable practical small-scale solutions for residential and offices use. The best stationary technology is probably the redox flow batteries. This article proposes the direct conversion of sunlight into electrochemical energy stored in a redox flow battery. A photoelectrochemical cell is used to charge a vanadium redox flow cell (CdS(s)|V3+, VO2+||V3+, V2+|Carbon Felt(s), E0=0.6 VNHE). A CdS thin film photoelectrode is prepared to directly charge the cell, pairs V3+/VO2+. CdS photoanode exhibits competitive photocurrents, when compared to other photoelectrochemical devices, 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 densities up to ca. 1.4mAcm−2. Finally, a tandem configuration is tested using a dye-sensitized solar cell and a CdS photoanoade creating ~1.3V of photovoltage. This tandem arrangement proves to charge conventional all vanadium redox cell (DSC/CdS(s)|VO2+, VO2+||V3+, V2+|Carbon Felt(s), E0=1.2 VNHE) without external bias.

Abstract A Bioelectrochemical System (BES) is used for charging an electrochemical fuel to be used in a Redox Flow Cell (RFC), demonstrating the first proof of concept of a microbially-charged electrochemical fuel. Geobacter sulfurreducens, electroactive bacteria, was used to charge anthraquinone-2,6-disulfonate (2,6-AQDS) producing current densities of ca. 200–500 mA m−2 and maximum power densities of ca. 33 mW m−2. The microbially-charged electrochemical fuel and potassium ferricyanide, K3[Fe(CN)6] were introduced in a RFC producing a potential difference of 0.62 V, with a ca. 80% energy conversion efficiency. The use of a BES for charging the posilyte of a RFC is now envisioned. The bio-conversion of waste biomass energy into electrochemical fuels (microbially-charged electrochemical fuel for negalyte and posilyte) for later use in a RFC to produce electricity is a promising approach of converting biomass into storable and easy to use energy.

AbstractThe intermittent nature of the sunlight and its increasing contribution to electricity generation is fostering the energy storage research. Direct solar charging of an auspicious type of redox flow battery could make solar energy directly and efficiently dispatchable. The first solar aqueous alkaline redox flow battery using low cost and environmentally safe materials is demonstrated. The electrolytes consist of the redox couples ferrocyanide and anthraquinone‐2,7‐disulphonate in sodium hydroxide solution, yielding a standard cell potential of 0.74 V. Photovoltage enhancement strategies are demonstrated for the ferrocyanide‐hematite junction by employing an annealing treatment and growing a layer of a conductive polyaniline polymer on the electrode surface, which decreases electron–hole recombination.

Given the intermittent nature of solar radiation, the large-scale use of solar energy requires an efficient energy storage solution. So far, the only practical way to store such large amounts of energy is in the form of a chemical energy carrier, i.e., a fuel. Photoelectrochemical (PEC) cells offer the ability to convert solar energy directly into chemical energy in the form of hydrogen. Cuprous oxide (Cu2O) is being investigated for photoelectrochemical solar water splitting since it has a band gap of 2.0 eV with favorable energy band positions for water cleavage; it is abundant and environmentally friendly. A major challenge with Cu2O is its limited chemical stability in aqueous environments. We present a simple and low-cost treatment to create a highly stable photocathode configuration for H2 production, consisting of steam treatment of the multilayer structures. The role of this treatment was investigated and the optimized electrodes have shown photocurrents over −5 mA cm−2 with 90% stability over more than 50 h of light chopping (biased at 0 VRHE in pH 5 electrolyte).