High-Throughput Synthesis and Characterization of PGM-Free PEFC Cathode Catalysts

Abstract

The high cost of platinum, widely used in the electrode of polymer electrolyte fuel cells (PEFCs), is one of main barriers to the widespread use of fuel cell vehicles. Many studies have focused on reducing the excessive production cost of the fuel cell stack by either decreasing the platinum loading using more active Pt-based catalysts and nanostructured alloys or developing platinum group metal-free (PGM-free) catalysts based on low-cost transition metals (e.g., iron and cobalt), carbon, and nitrogen. This presentation will describe high-throughput techniques for synthesis, physical and chemical characterization, hydrodynamic activity screening, electrode fabrication, and fuel cell performance testing of PGM-free catalysts under the auspices of the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Offices’ Electrocatalysis Consortium (ElectroCat) [1]. Argonne’s robotic systems have been utilized to rapidly synthesize unique iron and transition metal-nitrogen-carbon (TM-N-C) catalysts exploring a large number of variables such as nitrogen content, ZIF-8 content, Fe content, TM dopant, and Fe precursor. These variables have been shown to be important factors in determining the activity and stability of the resulting catalysts. The catalysts were synthesized using multi-port ball-milling and multi-sample heat treatment. The ORR activity of synthesized materials was characterized using a newly-developed multichannel flow double electrode cell (m-CFDE), allowing the aqueous hydrodynamic measurement of multiple samples simultaneously and using removable electrode plugs to facilitate the quick change of catalyst [2]. A custom-designed system was utilized to deposit the catalyst-ionomer inks onto the glassy carbon electrodes of the m-CFDE electrode plugs. This system is equipped with a nano-liter injector with exchangeable micro-tips and a computer-controlled XY table mount for the electrode plug to uniformly distribute the ink across the 3 mm x 1 mm glassy carbon electrodes. The ORR activity is correlated with catalyst Fe speciation, as determined using Fe K-edge X-ray absorption spectroscopy (XAFS) and also with catalyst BET and electrochemically-determined surface areas. A segmented 25-electrode array cell was used for the high-throughput performance testing of 25 different types of catalyst in a single membrane-electrode assembly (MEA). The automated electrode deposition system has been used in combination with a custom-designed heated vacuum table and a multi-channel peristatic pump to deposit 25 circular electrodes onto the membrane in the pattern required by the NuVant Systems Inc. array fuel cell hardware [3]. This automated ink dispensing system can be used for precise and even catalyst ink deposition across the small circular array electrodes while minimizing the amount of material required to form those uniform electrodes. This presentation will correlate the performance of the catalysts in the MEA with the catalysts’ ORR activity, physical and chemical properties, and synthesis parameters. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357.