Advanced Research on Fiber and Powder Electrodes for Fuel Cells and Redox Flow Batteries

Abstract

When fuel cell electrodes are prepared by coating or spraying a mixture of catalyst particles and polymer binder, there is little or no control of the multi-scale electrode morphology. Electrode structural features such as particle and binder interconnectivity, macro-porosity, and micro-porosity are difficult to control but are critically important when high-performance nanocatalysts are used. Nanofiber electrospinning is an electrode fabrication technique that can address these issues for next-generation high-performance fuel cells. Conventional powder catalyst fuel cell electrodes also suffer from poor durability (carbon corrosion and metal dissolution) which limits their operational lifetime. The use of chemical additives has shown some promise, but an improvement in electrode lifetime was usually accompanied by a loss in fuel cell power output. The use of fluoropolymer binders in fuel cells is also problematic, given the recent healthcare concerns regarding fluorinated “forever compounds.” This dissertation seeks to address deficiencies in nanofiber electrodes and sprayed powder electrodes for H2/air proton exchange membrane fuel cells, and H2/Br2 redox flow batteries. For sprayed powder electrodes, a hydrophobic additive was found that stopped carbon corrosion of a Pt/C catalyst cathode without sacrificing fuel cell power output, and a new hydrocarbon electrode binder was investigated which worked very well in a fuel cell cathode when mixed with a water-soluble pore former. To improve the compatibility of nanofiber electrospinning with commercial roll-to-roll fuel cell electrode manufacturing lines, a new fabrication method was developed where electrodes were prepared by spraying inks containing pre-formed electrospun fibers. Fiber electrodes were also used for the hydrogen electrode in a H2/Br2 redox flow battery, where a hydrophobic coating on the fibers prevented Pt dissolution by bromine species. In this talk, for each electrode system, the method for preparing the electrodes will be presented, experiments to evaluate the electrodes will be described, and experimental results will be discussed.