Investigation and Mitigation of Degradation in Hydrogen Fuel Cells
The ever increasing demand of petroleum in the transport sector has led to depletion of low cost/low risk reserves, increased levels of pollution, and greenhouse gas emissions that take a heavy toll on the environment as well as the national economy. There is an urgent need to use alternative energy resources along with an efficient and affordable energy conversion system to arrest environmental degradation. Polymer electrolyte fuel cells (PEFCs) show great promise in this regard - they use hydrogen gas as a fuel that electrochemically reacts with air to produce electrical energy and water as the by product. In a fuel cell electric vehicle (FCEV), these zero tail pipe emission systems offer high efficiency and power density for medium-heavy duty and long range transportation. However, PEFC technology is currently challenged by its limited durability when subjected to harsh and adverse operating conditions and transients that arises during the normal course of vehicle operation. The hydrogen-based fuel cell power train for electric vehicles must achieve high durability while maintaining high power efficiency and fuel economy in order to equal the range and lifetime of an internal-combustion-engine vehicle. The technology also needs to meet the cost targets to make FCEVs a commercial success. In this dissertation, one of the degradation phenomena that severely impede the durability of the system has been investigated. In scenarios where the cell becomes locally starved of hydrogen fuel, “cell reversal” occurs, which causes the cell to consume itself through carbon corrosion and eventually fail. Carbon corrosion in the anode disrupts the original structure of the electrode and can cause undesirable outcomes like catalyst particle migration, aggregation, loss of structural and chemical integrity. A comprehensive study using advanced electrochemical diagnostics and high resolution 3D imaging was performed and a new understanding to extend PEFC life time and robustness, by implementing engineered materials solutions, has been achieved. This will eventually help in making fuel cell systems more efficient, durable and economically viable, in order to better harness clean energy resources.