Novel direct liquid fuel cell - membraneless architecture and simple power and fuel crossover control

The convergence of multiple functions in portable electronics is resulting in greater power requirements and a reduced operation time. The incumbent battery technology is not projected to accommodate these requirements. An attractive alternative is the direct liquid fuel cell, in particular the polymer electrolyte membrane (PEM) based direct methanol fuel cell (DMFC), as it does not suffer from the disadvantages associated with conventional battery technology and has the potential for extended and continuous operation. However, the wide spread adoption of the DMFC is prevented by a significant number of barriers that include: fuel crossover, catalyst and fuel utilization, efficiency, overall cost and size. The research presented in this thesis aims to address these areas through the development of simplified cell architectures and operational methods. In a conventional membrane electrode assembly (MEA), a PEM is compressed between an anode and cathode electrode. In this research a new branch of simplified architectures that is unique from those that have been reported in literature has been developed by eliminating and/or integrating key components of a conventional MEA. The membraneless 3D anode approach was shown to be fuel independent and scaleable to a conventional bipolar fuel cell arrangement and exhibits comparable performance to a conventional passive DMFC at ambient conditions (25C, 1 atm). The single electrode supported DMFC was fabricated through a sequential deposition of an anode catalyst layer, an electrically insulating layer and a cathode catalyst layer onto a single carbon fibre paper substrate. This resulted in a 42% reduction in thickness and a 104% improvement in volumetric specific power density over a two electrode DMFC configuration. In addition, simple methods to control fuel crossover and power output were developed and characterized. A perforated graphitic diffusion barrier with engineered properties reduced fuel crossover in the range of ~73% to ~94%. The power output of the membraneless DMFC was controlled through a selective activation/deactivation of triple phase boundary regions on the electrode assembly with a physical guard. This method enabled the DMFC to operate at a single optimized condition where the voltage, current density, crossover and overall efficiency were constant at any power level.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat