Atomically Dispersed Isolated Fe–Ce Dual-Metal-Site Catalysts for Proton-Exchange Membrane Fuel Cells

Atomically dispersed single-metal-site catalysts are hailed as the most promising category for the oxygen reduction reaction (ORR) with full metal utilization and complete exploitation of intrinsic activity. However, due to the inherent electronic structure of single-metal atoms in MNx, it is difficult to break the linear relationship between catalytic activity and adsorption energy of reaction intermediates, and the performance of such catalysts still falls short of expectations. Herein, we change the adsorption structure by constructing Fe-Ce atomic pairs to modulate the iron d-orbital electron configuration, breaking the linear relationship based on single-metal sites. The 4f cruise electrons of cerium element reduce the d-orbital center of iron in the synthesized FeCe-single atom dispersed hierarchical porous nitrogen-doped carbon (FeCe-SAD/HPNC) catalyst, and more orbital-occupied states appear near the fermi level, which weakens the adsorption strength in the active center and oxygen species, so that the rate-determining step was shifted from *OH desorption to *O > *OH, rendering the excellent ORR performances of the FeCe-SAD/HPNC catalyst. The synthesized FeCe-SAD/HPNC catalyst shows excellent activity, with a half-wave potential as high as 0.81 V for ORR in 0.1 M HClO4 solution. Additionally, by constructing a three-phase reaction interface with a hierarchical porous structure, the H2-O2 proton-exchange membrane fuel cell (PEMFC) assembled with FeCe-SAD/HPNC as cathode catalyst achieves a maximum power density of 0.771 W cm-2 and good stability.