Although the ORR performance of NPMCs in the RDE tests is inspiring, further verification of their performance in fuel cell MEAs is still needed. Previous results on NPMC-based MEA are listed in Tab.1. Wan et al. [
22] reported a class of concave Fe-N-C single-atom catalysts with a peak power of 1180 mW/cm
2 at 0.47 V under 2.5 bar H
2-O
2 at 80 °C and 100% relative humidity (RH), which is the best performance reported thus far. This superior performance was ascribed to an enhanced external surface area and mesoporosity, which exposed more inaccessible Fe-N
4 moieties and promoted oxygen transport in catalyst layers (CLs). Chen et al. [
24] reported an MEA with 1100 mW/cm
2 peak power, measured under 1.5 bar H
2-O
2 at 80 °C and 100% RH, and a catalyst life of 20 h. They also designed experiments and density functional theory calculations to indicate that Fe at active sites of catalysts is attacked by hydroxyl free radicals formed by the decomposition of H
2O
2, and that the ionomer of the catalyst layer and the membrane are further contaminated by the leached Fe ions, which greatly affected the performance. Although the series of Fe-N-C catalysts have displayed similar catalytic activities to Pt, they rapidly degraded. In the previous study, Fe-N-C catalyst-based fuel cell exhibited an initial peak power density of 1100 mW/cm
2 but suffered a current loss of 52% over only 20 h at 0.4 V. On the one hand, Fe at active sites were attacked by hydroxyl free radicals formed by the decomposition of H
2O
2, and on the other hand, both the ionomer in CL and the membrane were contaminated by leached Fe ions. Several studies on NPMCs with metals such as Co and Mn have also been reported. It is believed that a high density of CoN
4 active sites not only results in higher power density but also leads to higher stability owing to their immunity to Fenton’s reaction [
26].