Transforming Single‐Atom Site to Dual‐Atom Site in Fe–N–C Catalysts: A Universal Strategy for Enhancing Durability in Proton‐Exchange Membrane Fuel Cells
Ruguang Wang, Jiaxin Guo, Jisi Li, Quanlu Wang, Zheng Lv, Cairong Gong, Caofeng Pan, Tao Ling
Abstract
Abstract Fe–N–C catalyst is the most promising non‐noble metal oxygen reduction catalyst for proton‐exchange membrane fuel cells (PEMFCs); however, their practical applications are still limited by unsatisfactory long‐term stability. This is because the N atoms of the active FeN 4 moiety are easy to protonate, leading to the leaching of Fe atoms, and the H 2 O 2 generated during oxygen reduction reaction (ORR) process triggers the Fenton reaction, further accelerating the dissolution of Fe. To address these critical stability challenge, we developed a general strategy to transform FeN 4 single‐atom sites to Fe 2 N 6 dual‐atom sites in Fe–N–C catalysts with various carbon substrates. This is achieved by treating the presynthesized Fe–N–C catalysts in a H 2 /Ar atmosphere to break the C─N bonds near the FeN 4 sites while introducing Fe and N precursors to form the Fe 2 N 6 sites. Our theoretical calculations and experimental results demonstrate that the newly formed Fe 2 N 6 sites are structurally more stable in acidic ORR and produce negligible H 2 O 2 (<1%). Therefore, the transformed Fe–N–C catalyst exhibits an extremely low Fe demetalation ratio (0.61 at%) in 0.1 M HClO 4 after 80k cycling. More surprisingly, the transformed Fe–N–C catalyst can effectively decompose H 2 O 2 with a high decomposition rate of 15.7 mmol min −1 , approaching that of the state‐of‐the art Pt/C catalyst (17 mmol min −1 ). As a result, the transformed Fe–N–C catalyst assembled PEMFC operates stably for 300 h with only 7% current density attenuation, whereas that of the pristine Fe–N–C catalyst‐based device declines by 84% within 100 h.