Design and fabrication of photoelectrochemical membranes for integrated, solar-driven hydrogen fuel generation

• Main Author: McDonald, Michael Blaine
• Other Authors: Freund, Michael S. (Chemistry)
• Published: 2015
• Subjects: hydrogen; membrane; energy
• Online Access: http://hdl.handle.net/1993/30205

Arguably the greatest confrontation for humanity and the Arguably the greatest confrontation for humanity and the natural world is addressing the shortfalls of our current energy sources and the threat that intensive consumption has on the environment. By harvesting the immense energy of the sun and converting it into clean fuels such as H2, these issues may be resolved. Inefficiencies of current technology have made the realization of an energy changeover extremely challenging. A viable solution would be an integrated system of the absorbing and conversion components embedded in a membrane. The membrane must house the electrode assembly, block product crossover, and manage ionic and electronic charges generated while remaining passive to the photoelectrochemical process. The first approach to developing such a membrane involves the formation of a composite of the electrically conducting polymer PEDOT and the inorganic acid PMA. It was found that the material possessed excellent electrical conductivity as a function of pH and oxidation state, and stability against overoxidation, while the ionic conductivity remained insufficient. This was combatted with the addition of the proton conductor Nafion®, which was combined in the desired ratio to optimize the material conductivities. Membranes capable of maintaining steady-state pH gradients, with the motivation to operate the oxygen- and hydrogen-generating sides in their optimal pH, were also investigated. It is herein confirmed that these membranes are able to maintain a pH gradient of 14 units indefinitely while adding no additional thermodynamic perturbance to the system. Membranes were constructed by combining ion exchange layers with interchangeable materials in an interfacial layer to develop a photoelectrochemically-adapted membrane. A transparent conducting oxide, conducting polymer, and graphene materials were selected, with the former two exhibiting inadequate activity. However, it was found that graphene oxide demonstrates activity that is comparable or better than commercially available membranes. Its presence also stabilized the membrane. The shortfall of graphene oxide is that it is an insulator. Chemical reduction was used to introduce electrical conductivity by removing the functional groups, which was controlled by the exposure conditions. It is shown that a reduced graphene oxide membrane can meet the figures of merit outlined for these integrated energy systems.