Low‐PGM and PGM‐Free Catalysts for Proton Exchange Membrane Fuel Cells: Stability Challenges and Material Solutions

Abstract

Fuel cells as an attractive clean energy technology have recently regained popularity in academia, government, and industry. In a mainstream proton exchange membrane (PEM) fuel cell, platinum‐group‐metal (PGM)‐based catalysts account for ≈50% of the projected total cost for large‐scale production. To lower the cost, two materials‐based strategies have been pursued: 1) to decrease PGM catalyst usage (so‐called low‐PGM catalysts), and 2) to develop alternative PGM‐free catalysts. Grand stability challenges exist when PGM catalyst loading is decreased in a membrane electrode assembly (MEA)—the power generation unit of a PEM fuel cell—or when PGM‐free catalysts are integrated into an MEA. More importantly, there is a significant knowledge gap between materials innovation and device integration. For example, high‐performance electrocatalysts usually demonstrate undesired quick degradation in MEAs. This issue significantly limits the development of PEM fuel cells. Herein, recent progress in understanding the degradation of low‐PGM and PGM‐free catalysts in fuel cell MEAs and materials‐based solutions to address these issues are reviewed. The key factors that degrade the MEA performance are highlighted. Innovative, emerging material concepts and development of low‐PGM and PGM‐free catalysts are discussed.

Biomass‐derived nonprecious metal catalysts for oxygen reduction reaction: The demand‐oriented engineering of active sites and structures

“…[30][31][32][33][34][35][36][37][38] Two of most representative types of PGM-free ORR catalysts, the heteroatom (eg, N) doped carbon [39][40][41][42] and the transition metal (eg, Fe) coordinated with N in carbon matrix 11,[43][44][45] have been well accepted as the promising candidates to replace PGM-based materials. In both cases, carbon is the major component 46 ; even for the PGM-based ORR catalysts, carbon support is an important investigation topic. 47 Therefore, study of carbon support is crucial for the research and development of PGM-free ORR catalysts.…”

Calibration of computational Mössbauer spectroscopy to unravel active sites in FeNC catalysts for the oxygen reduction reaction

“…[45] However, the stability and hence the long-term usability of FeNC materials is still lacking. [46][47][48] An important step toward a better understanding of this promising substitution material for platinum electrodes is to clarify the structure and electronic properties of the active site. [39,43,49,50] The current consensus in the literature is that the catalytically active iron ion is surrounded by 2-4 nitrogen donor atoms embedded in a graphene sheet that may have structural or electronic defects and possibly an additional axial ligand.…”

Mapping Localized Peroxyl Radical Generation on a PEM Fuel Cell Catalyst Using Integrated Scanning Electrochemical Cell Microspectroscopy

“…PEFCs have been identified as a promising source of renewable energy for future transportation applications, but are currently limited in their use by the prohibitively high costs and performance degradation of the Pt-group metal (PGM)based cathodes required to promote the ORR (Litster and McLean, 2004;Hess et al, 2011;Debe, 2012;Epting and Litster, 2012;Houchins et al, 2012;Coleman and Co, 2015;Hu et al, 2019). Various metal oxides and alternative organometallics have been investigated as low Pt and PGM-free catalysts for the ORR (Ishihara et al, 2008;Coleman and Co, 2014;Du et al, 2020). Perhaps the most active PGM-free ORR catalysts are ligated iron species formed by sintering of organometallic precursors with argon or nitrogen (Lefèvre et al, 2009;Sun et al, 2017;Zhang et al, 2017;Li et al, 2019).…”

“…Perhaps the most active PGM-free ORR catalysts are ligated iron species formed by sintering of organometallic precursors with argon or nitrogen (Lefèvre et al, 2009;Sun et al, 2017;Zhang et al, 2017;Li et al, 2019). Unfortunately, leached iron from ligated iron catalysts promotes decomposition of intermediate hydrogen peroxide, formed during the ORR, into ROS (Wang et al, 2019;Du et al, 2020). In addition to the deleterious effects of ROS generation, other components of PEFCs are especially sensitive to radical formation.…”

“…Specifically, the polymer membrane will degrade in the presence of ROS, eventually forming pinholes that lead to complete cell failure (Mittal et al, 2006;Coms, 2008;Gubler et al, 2011). Substantial ROS generation persists even in iron-free and PGM-free ORR catalysts, emphasizing the importance of this reaction (Wang et al, 2019;Du et al, 2020).…”