For polymer electrolyte membrane fuel cells (PEMFCs) in fuel cell electric vehicles (FCEVs), the cell reversal (CR) caused by fuel starvation, rapid load change, low catalyst performance, etc., results in irreversible damage to the anode of a membrane electrode assembly (MEA).[1] Nonetheless, the consequences of the CR can be alleviated by a smart anode material design such as adding additives to the anode electrode that enable oxygen evolution when CR protection is needed, or using dual functioning material that features both hydrogen oxidation reaction (HOR) and oxygen evolution reaction (OER) activities.[1-4]

The objective of this work is to suggest the cell reversal tolerant, non-Pt anode MEA without significantly risking the MEA IV performance. Specifically, how each composing material, the catalyst metal and the supporting carbon affects the anode’s CR tolerance under fuel deficient state during the MEA operation, was investigated. Ketjenblack® 300J was selected for the carbon support and as-purchased Ketjenblack® was heat-treated to learn the degree of graphitization’s influence on the carbon corrosion tolerance during the CR. The as-obtained carbon support and those treated at 1000°C, 2250°C, and 2800°C, were denoted as KB, 10KB, 22KB, and 28KB, respectively. The carbon supports were characterized with N₂ adsorption and Raman spectrometer for the estimation of the graphitization . The material of choice for the active anode catalyst metals was restrained to Ir, Ru, and their binary alloys because they exhibit both HOR [5] and OER activities. [6] The dispersing metals were varied from a single component to binary components with differing compositions (Ir:Ru = 1:0, 1:1, 1:2, 1:4, 1:6, 0:1 (mol/mol)). Ir_xRu_y/C, the Ir and Ru binary alloy with atomic ratio of x:y dispersed on carbon, were synthesized by a simple impregnation method using metal salts and carbon support and a successive reduction in a hydrogen atmosphere at 300°C. The synthesized catalysts were characterized with XRD, ICP, and TGA for physicochemical properties. The synthesized Ir_xRu_y/C and Pt/C purchased from commercial supplier were each applied to the anode in the MEA, and the single-cell IV performance testing was carried out at various operating conditions (cell temperature, relative humidity, and back pressure). The cell reversal tolerance of Ir_xRu_y/C and commercial Pt/C anode MEAs was measured by subjecting each MEA to the anode’s fuel starvation condition.

Among various Ir to Ru compositions, IrRu₄/22KB, IrRu₄ supported on 22KB, anode MEA showed the best IV performance and incomparable cell reversal tolerance over conventional Pt anode MEA. It should be highlighted that IrRu₄ acted as a sole component for the anode active material, not just as an additive. Moreover, when the active catalysts were dispersed on a highly graphitized support, 28KB, the cell reversal durability was enhanced by a factor of ~10. The binary alloy of OER-active Ir and Ru (preferably IrRu, IrRu₂, and IrRu₄) is a promising anode component that features both hydrogen oxidation and good cell reversal tolerance in an MEA.

References

[1] C. Qin, J., D. Yang, B. Li, and C Zhang, Catalysts, 6, 197 (2016)

[2] B. K. Hong, P. Mandal, J.-G. Oh, and S. Litster, J. Power Sources, 328, 280 (2016)

[3] K.H. Lim, W. H. Lee, Y. Jeong, and H. Kim, J. Electrochem. Soc. 164 (14) F1580 (2017).

[4] E. You, M. Min, S.-A. Jin, T. Kim, and C. Pak, J. Electrochem. Soc. 165 (6) F3094 (2018).

[5] S. A. Jin, C. Pak, D. J. Yoo, and K. H. Lee, US 2013/0137009 A1, (2013).

[6] R. T. Atanasoski, L. L. Atanasoska, D. A. Cullen, G. M. Haugen, K. L. More, and G. D. Vernstrom, Electrocatal., 3, 284 (2012).