Fe single atoms in N‐doped C (Fe‐N‐C) present the most promising replacement for carbon‐supported Pt‐based catalysts for the O2 reduction reaction at the cathode of proton exchange membrane fuel cells (PEMFCs). However, it remains unclear how the I/C ratio affects Fe‐N‐C degradation and the stability of single Fe atom active sites (FeNx). Here, an accelerated stress test (AST) protocol is combined with emerging electrochemical techniques for a porous Fe‐N‐C in PEMFC with a range of I/C ratios. The PEMFC current density degradation rates are found to be comparable; however, with increased I/C ratio the additional FeNx sites accessed are more stable, as shown by their higher active site stability number (electrons passed per FeNx lost) at the end of the AST protocol. Meanwhile, the initial rate of TOF decay is suppressed with increasing I/C. Electrochemical process changes are studied via distribution of relaxation times analysis. Minor changes in H+ and O2 transport resistance at low current density prove kinetic degradation dominants at high potentials. These findings demonstrate how electrochemical techniques can be combined with stability metrics to determine and deconvolute changes from the active site to device level electrochemical processes in PEMFCs.

中文翻译：

---

质子交换膜燃料电池中的 Fe-N-C：离聚物负载对降解和稳定性的影响


N 掺杂 C （Fe-N-C） 中的 Fe 单原子是质子交换膜燃料电池 （PEMFC） 阴极 O2 还原反应的碳负载 Pt 基催化剂的最有希望的替代品。然而，目前尚不清楚 I/C 比率如何影响 Fe-N-C 降解和单个 Fe 原子活性位点 （FeNx） 的稳定性。在这里，加速应力测试 （AST） 方案与新兴的电化学技术相结合，用于 PEMFC 中具有一系列 I/C 比率的多孔 Fe-N-C。发现 PEMFC 电流密度衰减率具有可比性;然而，随着 I/C 比率的增加，访问的额外 FeNx 位点更加稳定，如 AST 协议结束时它们更高的活性位点稳定性数（每 FeNx 丢失的通过的电子数）所示。同时，TOF 衰减的初始速率随着 I/C 的增加而受到抑制。通过弛豫时间分布分析研究电化学过程变化。在低电流密度下 H+ 和 O2 传输电阻的微小变化证明，在高电位下动力学降解占主导地位。这些发现展示了如何将电化学技术与稳定性指标相结合，以确定和去卷积 PEMFC 中从活性位点到器件级电化学过程的变化。