Fabrication and Scale-up of Highly Durable Heavy Duty Fuel Cell MEAs

Abstract

Medium and heavy-duty PEM fuel cells operate under much harsher conditions than light duty fuel cells and are expected to last 25,000-30,000 hours in the field. These systems must operate successfully in the presence of impurities, starting and stopping, freezing and thawing, humidity and load cycling. Therefore, materials, components, and interfaces used in such systems must be highly resistant to severe mechanical and chemical stress.Novel, highly active stable Pt and ordered PtCo intermetallic nanoparticles with well-controlled particle size and composition have been synthesized on a highly efficient PGM-free single metal active site rich carbon, to maximize their synergistic effects for enhanced performance and durability. Integrating these catalysts integrated with high O2 permeability ionomer (HOPI) in membrane electrode assemblies (MEAs) improved their fuel cell performance and durability, allowing the MEAs to achieve >600 mA/mgPt at 0.9 VIR-free with a mass activity loss < 30% after 150k square wave accelerated stress test (AST) cycles; and > 600 mA/cm2 (~65% efficiency) at 0.8 V, with a performance loss < 40 mV after 150K AST cycles.In a PEM fuel cell, the catalyst ink formulation and mixing processes control catalyst layer coating quality, electrode morphology, and the resulting fuel cell performance and durability. Catalyst ink properties are a result of complex solvent-catalyst-ionomer interactions that depend on the mixing method employed. Here, we compare the performance and durability of electrodes made from bath sonicated inks for ultrasonic spray coating before and after the catalyst scale up. Ink rheology and catalyst particle size are used to correlate ink properties to electrode morphology and structure and ensure consistency from batch to batch, and from small lab scale to subsequent scale-up. We evaluate and discuss the challenges that arise when transitioning from spray coating catalyst ink on a small scale, directly on a membrane, to coating more viscous inks on gas diffusion layers (GDLs), made via Mayer rod coating of ball milled inks, in anticipation of developing a roll-to-roll (R2R) fabrication process. The MEA performance and durability of the novel catalyst was also evaluated under heavy duty operating conditions using M2FCT’s AST, i.e., in H2/Air, 90 ⁰C, and 50% RH.This work provides a comprehensive understanding of interactions between Pt, PtCo, carbon, ionomer, membrane, and GDLs and their impact on electrode structure, fuel cell performance and durability, as well as considerations for scale up to a R2R fabrication process. The attained information will be used to improve fuel cell electrode design, fabrication and scale-up.Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-SC0021671. Figure 1. (a) Comparison of H2-air fuel cell performance of HOPI-based CCMs prepared with different volume ratios of H2O to n-propanol (nPA). (b) Dependence of fuel cell performance at 0.8 and 0.7 V of the CCMs prepared with different volume ratios of H2O to nPA. (c) MEA performance of the best performing Pt (40 wt. %)/Mn-N-C MEA under various relative humidity. (d) The high-frequency resistance (HFR) of HOPI-based CCMs prepared with a volume ratio of 2:1. All of the tests were performed with a 5 cm2 differential cell with 14 parallel channels. The cell temperature was 80 ⁰C, the flow rates for H2 and air are 500 and 2000 sccm, and the backpressure is 250 kPaabs. The Pt loading in the anode and cathode are 0.1 and 0.2 mgPt/cm2, respectively. Figure 1