Hydrogen and Fuel Cell Materials
Argonne chemist Nancy Kariuki with a cell designed to probe the atomic structure, oxidation state, and size distribution of polymer electrolyte fuel cell catalysts during polarization in an aqueous electrochemical environment using X-ray absorption and X-ray scattering. These experiments elucidate the catalysts’ physical and chemical properties responsible for catalytic activity and the mechanisms behind the loss of activity. This atomic-level insight enables the design of more active, less expensive, and more durable catalysts.
Polymer electrolyte fuel cell (PEFC) systems are promising alternatives to conventional power systems for transportation, other portable, and stationary applications due to their high efficiency of converting fuel to electricity, low emissions, and low operating temperatures. The fuel of choice for many PEFC power applications is hydrogen, due to the high efficiency at which this fuel can be converted to electricity, its high energy density per mass of fuel, and non-carbon-containing emissions. Three major issues impeding widespread implementation of PEFC power systems based around hydrogen, especially for portable and transportation use, are cost, lifetime, and fuel storage. The Hydrogen and Fuel Cell Materials group has active research projects to develop new materials and enable existing materials to overcome the major barriers to enable the use of this promising technology in a variety of applications.
The research in the Hydrogen and Fuel Cell Materials group addresses the two main issues facing the widespread deployment of PEFC power systems: cost and durability. The group’s research also addresses one of the main issues facing the use of fuel cells for transportation applications: lack of suitable high capacity hydrogen storage materials.
A major cost contributor to PEFC power systems is the platinum-based fuel cell catalyst. To address this issue, the Hydrogen and Fuel Cell Materials group is developing platinum group metal-free (PGM-free) catalysts and enabling the use of lower loadings of platinum by enhancing platinum’s catalytic activity and maximizing its performance in the fuel cell. The group is developing PGM-free catalysts using approaches and materials that maximize the active site density and accessibility of these active sites, including nano-networks of electro-spun zeolitic imidazole frameworks (ZIFs) and porous organic polymers (POPs).
The group is also accelerating the development of PGM-free catalysts by developing and utilizing high-throughput materials synthesis, characterization, and performance evaluation equipment and methodologies. The foundation of this research are the capabilities within the Chemical Sciences and Engineering division’s high-throughput research laboratory. This activity is a cornerstone of the Department of Energy’s ElectroCat research consortium, which is co-led by Argonne and Los Alamos National Laboratory.
Another of the group’s research areas focuses on achieving high performance from advanced platinum alloy electrocatalysts by tuning the electrode layer composition and structure. The approach seeks to determine the performance-limiting properties of the platinum alloy catalysts and electrodes utilizing a combination of in-cell diagnostics and structural analyses of catalyst, electrode layer precursor solutions, and electrodes using X-ray scattering, X-ray spectroscopy, and X-ray tomography techniques at Argonne's Advanced Photon Source. The information from these characterizations and the impact of electrode layer composition and precursor solution solvent on the performance and structure are used to inform the design of electrodes with technology-enabling performance.
The group is addressing the limited durability of PEFCs by identifying the mechanisms of catalyst degradation and determining the catalyst, catalyst support properties, and operating conditions that limit catalyst lifetime. This research utilizes ex situ, in situ, and in operando X-ray absorption and scattering techniques at Argonne’s Advanced Photon Source, aqueous dissolution studies, modeling of platinum dissolution and de-alloying, and modeling of the effect of catalyst degradation on cell performance, in collaboration with Argonne’s Nuclear Engineering Division.
Although hydrogen is the fuel of choice for these applications, it has a low energy density per unit volume and, as such, storage as a compressed gas is limited in capacity and also and its storage as a compressed gas has limited capacity and compression is also energy intensive. Therefore, the group is working to develop lightweight and compact materials that can store large amounts of hydrogen at ambient temperatures, release hydrogen quickly at PEFC temperatures, and recharge quickly and easily. Two hydrogen storage materials classes we are developing include chemical hydrides, such as graphene-wrapped borohydrides, and high surface area, highly-porous adsorbents, such as porous organic polymer and metal organic frameworks.