Fuel cells (FC) are electrochemical devices that convert chemical energy into electricity and heat without a combustion process. The converting process is efficient and environmentally friendly. In addition, unlike batteries, which generate limited power because finite amounts of chemicals are stored inside, fuel cells can continue to produce electricity as long as the fuels (such as hydrogen) and oxygen/air are being supplied.
Among a variety of FC systems, Polymer electrolyte membrane (PEM) fuel cells - also called proton exchange membrane fuel cells is the most promising system for transportation as well as small scale stationary power generation applications. The advantages of PEMFC include low operating temperature (typically, > 85 C, allowing to start quickly because of less warm-up time), high power density, and immediate response for power demand change.
The proton exchange membrane (PEM) is the central part in a PEMFC system and has a major influence on the system's overall performance and operating conditions. Current PEMs (such as Dupont's Nafion) function well only under high humidity conditions. PEMFCs based on these membranes are limited to operating temperatures of 60-80 C and require external humidification to maintain optimum performance. Maintaining these temperatures under automotive conditions, especially at peak power, requires over-sized cooling equipment. In addition, the humidification requirements add increased volume, weight, and complexity to the system. These issues would be reduced or eliminated if a PEM could be operated at higher temperatures (approximately 120 C) and low humidity conditions. Additional benefits of operation at elevated temperatures and reduced humidity are a reduction in the occurrence of cathode flooding at peak power, a possible improvement in cell performance due to increased rate of the oxygen reduction reaction, and direct use of reformed fuel derived from an alcohol or hydrocarbon fuels (typically containing small amount of CO) by enhancing Pt catalyst tolerance to CO.
High temperature, low humidity membranes are expected to improve thermal management and ease or eliminate the need for membrane water management in automotive systems. Higher temperature operation will also aid in achieving success in combined heat and power applications for stationary fuel cells.
UTD Fuel Cell Research Group seeks novel polymer and organic/inorganic hybrid candidate materials for PEMs that conduct protons at low relative humidity (i.e., 25-50% RH) and temperatures ranging from room temperature to 120C.
How does a PEM Fuel Cell work?
A key part of a PEMFC system is a membrane electrode assembly (MEA), which consists of a proton exchange membrane (PEM) and two porous Pt catalyst layers coated onto either side of the membrane, working as cathode and anode (illuminated in the Figure below). Under operating conditions, hydrogen is fed into the anode side and oxidized into protons H+ (Equation 1), and oxygen (air) is fed into the cathode side and reduced into H2O (Equation 2). Protons formed on the anode pass through the membrane and combine with oxygen on the cathode to form H2O. Electrons generated at the anode pass through an external circuit to the cathode and supply power to the external circuit.