Self-supported metal aerogel electrocatalysts for oxygen reduction reaction: Opportunities and challenges

The development of highly active and stable electrocatalysts for the oxygen reduction reaction (ORR) remains a challenging task for improving the efficiency of fuel cells. Although Pt and Pt–transition metal alloy-based catalysts stand out as practical choices, they suffer from poor Pt utilization and stability. In this regard, highly electrically conducting, purely metallic, hierarchical 3D-porous, and nanowire aerogels as self-supported electrocatalysts have gained interest in recent decades. Metal aerogels are regarded as efficient catalytic materials, especially for electrocatalysis, as they integrate the unique features of both metallic and porous aerogels. In this review, we provide an overview of the recent progress in metal aerogel catalysts for ORR. Metal aerogel catalysts exhibit excellent ORR activity due to their high intrinsic activity arising from excellent Pt utilization and the exposure of active sites due to their metallic nature. Owing to their high Pt utilization, several noble metal aerogel catalysts were found to exhibit higher mass activity than traditional Pt/C catalysts and a mass activity target of 440 A per g Pt at 0.9 V vs. RHE, suggesting the high potential of metal aerogels as ORR catalysts in fuel cells. Herein, we summarize the recent benchmark research outcomes of metal aerogel catalysts for the ORR, their effects on the microstructure of catalyst layers, fuel cell performance, and cutting-edge modifications of recently reported metal aerogel catalysts. We systematically review the various aspects of metal aerogel catalyst synthesis, their advantages over traditional Pt/C catalysts, and ORR kinetics, and provide future research directions and recommendations to further improve and integrate metal aerogel catalysts into realistic fuel cells.