UBC Theses and Dissertations
Photocathodic composite conductive polymer-titania films for use in solar hydrogen generation Bruce, David R.
Green hydrogen generation can serve as a solution to energy storage needs of the 21st century if coupled with a renewable energy source such as solar power. There is an advantage to performing in-situ hydrogen generation at a photocatalytic surface in order to reduce system efficiency losses. Investigation into the limitations and benefits of coupled electrolytic and solar process are investigated in this dissertation. Of chief examination were polybithiophene-titania composite films used as a photocathode in a Nafion 117 membrane based H₂SO₄ electrolytic system. Titania content inclusion up to 0.35 mg/cm² with a range of film thicknesses between 1-20 μm, were investigated in several architectural configurations. The placement of the composite films was directed either towards or away from the proton conducing membrane in a 2-D or 3-D configuration. The results indicated that the electrochemical benefits to titania inclusion and film thickness increase were counter to photonic energy collection. With an increase in titania there was an increase in electrochemical performance, but it led to worse photonic efficiency as suspected due to an increase in recombination from defect trap states. With an increase in film thickness there was an increase in photonic efficiency with increased photon absorption, but this was accompanied by an increase in cell resistance leading to worse electrochemical performance. Electrochemical performance was also enhanced by placing the catalytic film directly against the membrane, although photonic stimulation in this configuration was impossible in our current cell configuration. Photonic stimulation was enhanced by the deposition of the composite films onto a distributed 3-D carbon fibre substrate. Doping of the 3-D composite films loaded on carbon fibre substrates with a Nafion ionomer interconnect was tested in an effort to enhance the triple phase connectivity of the cell. It was found that the doping resulted in a deactivation of the substrate (both electrochemical and photonic) due to the deposition method used, but increases in photonic performance at higher current densities showed that with less catalyst encapsulation this strategy may be a viable method to enhance PEM based photoelectrochemical cells.
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