Invited Paper VT-TuA9
Enabling Hydrogen as an Energy Carrier through Analytical Electron Microscopy

Tuesday, October 22, 2019, 5:00 pm, Room A213

Hydrogen is an important energy carrier which can be produced from renewable or intermittent energy sources for use in markets ranging from metal refining to transportation. Polymer electrolyte membrane fuel cells (PEMFCs) are a key technology for converting the chemical potential energy of hydrogen in electrical energy and driving down the cost of these systems is important towards enabling a hydrogen economy. At the heart of the matter is the membrane electron assembly (MEA), which consists of an anode and cathode separated by a proton-conducting membrane. Pt-based catalysts are typically used to drive the sluggish oxygen reduction reaction (ORR) at the cathode and are responsible for much of the cost of the MEA. Near term approaches to reduce Pt loading and hence cost involve the development of Pt-alloy catalysts which show exceptionally high mass activity but require improvements in durability. Long-term solutions will require the development of stable platinum group metal-free (PGM-free) catalysts, with current best-in-class candidates being derived from transition metal doped metal organic frameworks (MOFs). In both approaches, accelerated materials discovery and development is required to keep pace with increasing market and performance demands.

To this end, scanning transmission electron microscopy (STEM) has been employed to study MEAs from the atomic to micron scale. The application of atomic-resolution spectroscopic techniques to assess the quality and durability of Pt-alloy and PGM-free electrocatalysts will be presented. At a wider scale, the impact of particle dispersion, hierarchal porosity and proton-conducting ionomer distribution will be linked to electrochemical performance limitations through quantitative STEM imaging and energy dispersive X-ray spectroscopy (EDS). Finally, the movement of dissolved species across the membrane and gaseous diffusion layer will be explored to explain durability losses during fuel cell cycling. The synergy between electron microscopy and other characterization techniques such as X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and Mossbauer spectroscopy will also be discussed

Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE), as part of the FC-PAD and ElectroCat Consortia, which is part of the Energy Materials Network. Microscopy performed as part of a user project at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE Office of Science User Facility.