Abstract:
Proton Exchange Membrane (PEM) fuel cells are attractive alternatives for powering automotive applications via direct conversion of chemical energy stored in H¬2 fuel to electricity. They are widely considered as the primary power source for heavy-duty truck applications due to high-efficiency and zero-local emission. PEM fuel cell consists of anode and cathode electrodes sandwiched between a proton-conducting solid electrolyte, typically a perfluorosulfonic acid (PFSA) membrane. Anode reaction features the kinetically rapid H2 oxidation reaction (HOR) to protons and electrons. Protons travel across the membrane while the electrons travel across the external circuit generating current. They both recombine with O2 on the cathode to yield H2O. While anode electrode utilizes Pt electrocatalyst for HOR, Pt or Pt-based alloys such Pt3Co is utilized on the cathode for O2 reduction reaction (ORR).
The current state of the art carbon-supported platinum (Pt/C) or platinum-cobalt (Pt3Co/C) nanoparticle-based catalyst used for ORR are the most active and industrially relevant materials, but they face major durability challenges in fuel cell operating conditions. Pt/Pt3Co electrocatalysts at the fuel cell cathode operate at a low pH (~0 to 1), high temperature (~80 to 105 °C), and high potential (~0.65 to 1 V) all of which present a fertile condition for Pt and Co corrosion. Major degradation mechanisms include a) dissolution-redeposition of Pt nanoparticles, b) migration-coalescence of Pt nanoparticles and b) Co dissolution and contamination of the fuel cell membrane. In this presentation, a few strategies for mitigating these aspects of durability challenges will be discussed. These include a) system level operational strategies such as the use of lower relative humidity (RH) to mitigate Pt/Co dissolution, b) materials strategies such as the use of Pt-rich alloys (Pt5Co, Pt7Co) to mitigate Co dissolution, or c) the use of anchoring agents such as ZrO2 on the carbon support to mitigate Pt migration/coalescence. Recent successes in developing catalyst nanoparticles with a combination of better system-level and materials-level strategies will be discussed.
Speaker Bio:
Dr. Nagappan Ramaswamy is currently a Senior Research Engineer at the Global Fuel Cell Activities Division, General Motors Corporation located at Pontiac, Michigan USA. He received his Bachelor of Chemical & Electrochemical Engineering degree from Central Electrochemical Research Institute, India in 2005 and a Ph.D. degree in Chemistry from Northeastern University, USA in 2011. He is currently leading a U.S. Department of Energy funded research effort to develop durable catalysts and membranes for fuel cell applications geared towards heavy-duty truck applications.