Most transport fuels are derived from fossil fuels, generate greenhouse gases, and consume significant amounts of
water in the extraction, purification, and/or burning processes. The generation of hydrogen using solar energy to split
water, ideally from abundant water sources such as sea water or other non-potable sources, could potentially provide an
unlimited, clean fuel for the future. Solar, electrochemical water splitting typically combines a photoanode at which
water oxidation occurs, with a cathode for proton reduction to hydrogen. In recent work, we have found that a
bioinspired tetra-manganese cluster catalyzes water oxidation at relatively low overpotentials (0.38 V) when doped into
a Nafion proton conduction membrane deposited on a suitable electrode surface, and illuminated with visible light. We
report here that this assembly is active in aqueous and organic electrolyte solutions containing a range of different salts
in varying concentrations. Similar photocurrents were obtained using electrolytes containing 0.0 - 0.5 M sodium
sulfate, sodium perchlorate or sodium chloride. A slight decline in photocurrent was observed for sodium perchlorate
but only at and above 5.0 M concentration. In acetonitrile and acetone solutions containing 10% water, increasing the
electrolyte concentration was found to result in leaching of the catalytic species from the membrane and a decrease in
photocurrent. Leaching was not observed when the system was tested in an ionic liquid containing water, however, a
lower photocurrent was generated than observed in aqueous electrolyte. We conclude that immersion of the membrane
in an aqueous solution containing an electrolyte concentration of 0.05 - 0.5M represent good conditions for operation
for the cubium/Nafion catalytic system.
We discuss the preparation and performance of various electrochromic devices based on sol- gel deposited thin films. The films are deposited by dip-coating from alcohol-based sol-gel precursor solutions and the process is well suited to scaling up to large areas for window production. The coloration and bleaching performance of the devices is compared with the performance of individual films colored in liquid electrolytes, as well as with devices deposited using sputtered and evaporated films. Devices are based on sol-gel deposited tungsten oxide thin films which forms the active electrode. A range of counter-electrode materials have been tested, including sol-gel deposited vanadium pentoxide and titania films. Various ion conductors have been tested with these films, including simple, doped PEO and hartolyte, as well as a range of other polymers and inorganic ion conductors. Results will be presented showing the optical switching performance of the devices and comparing the performance of the devices with other device configurations. Initial results show that the sol- gel-based devices exhibit good switching performance, but the devices are sensitive to the details of the precursor solution used. Long term switching performance is an important issue in window applications, and the behavior of the sol-gel deposited films under repeated cycling will also be discussed, in particular a significant difference between the performance in liquid electrolytes and solid-state devices.
Electrochromic tungsten oxide thin films produced by dip-coating from a sol-gel solution are of interest for large area electrochromic window applications. The influence of the sol-gel formulation and the subsequent processing of the film required to produce uniform WO3 films are discussed together with the effects of the dipping and processing parameters on the structure, optical properties, and electrochemical behavior of the films. The electrochemical behavior of the films has been studied using cyclic voltammetry. Electrolyte solutions, with different cations for insertion into the WO3 layers, have been used in this work, and the resultant coloration of the films studied using spectrophotometry. Both colored and uncolored films have been studied using Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM). The sol-gel processing steps are shown to have a significant influence on the film microstructure and therefore the electrochemical coloration behavior of the films, as well as the lifetime of the film under repeated cycling. Results are shown illustrating the coloration behavior of the films, and the transmittance of the films over the visible and near-infrared spectra. WO3 films approximately 0.15 micrometers thick are highly transparent and color quite uniformly, although the process is not completely reversible. There is evidence from the auger electron spectroscopy (AES) and RBS data that there is residual carbon in the films after conventional processing. Some progress has been made toward examination of the effect of this carbon on both coloration efficiency and long-term switching life of prototype devices.