Advanced approach for active and durable proton exchange membrane fuel cells: Coupling synergistic effects of M-N-C nanocomposites

Atomically dispersed metal and nitrogen co-doped carbon (M-N-C) is a promising oxygen reduction reaction (ORR) catalyst for electrochemical energy storage and conversion applications but typically suffers from low durability and activity under the acidic conditions of practical polymer electrolyte exchange membrane fuel cells (PEMFCs). Recently, the performance of M-N-C nanocomposites under acidic ORR conditions has been enhanced by exploiting the synergistic coupling effects of their constituents (single-atom sites, nanoclusters, and nanoparticles). The unique geometric structures formed by the coupling of diverse sites in these nanocomposites provide optimal electronic structures and efficient reaction pathways, thus resulting in high activity and long-term durability. This work provides an overview of M-N-C nanocomposites as ORR electrocatalysts under practical PEMFC conditions, focusing on activity and durability enhancement methods and highlighting the strategies used to prepare electrocatalytically efficient M-N-C nanocomposites containing no or low amounts of platinum group metals. Progress in the development of advanced M-N-C nanocomposites as acidic ORR catalysts is discussed, and the pivotal role of synergistic effects resulting from the coupling sites within the nanocomposites is explored together with the characterization methods used to elucidate these effects. Finally, the challenges and prospects of developing M-N-C nanocomposites as next-generation electrocatalysts are presented.image