Mn- and N- doped carbon as promising catalysts for oxygen reduction reaction: Theoretical prediction and experimental validation
Mn- and N- doped carbon as promising catalysts for oxygen reduction reaction: Theoretical prediction and experimental validation
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DOI：
10.1016/j.apcatb.2018.10.034
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发表时间：
2019-04-01
影响因子：
22.1
通讯作者：
Wang, Guofeng
中科院分区：
文献类型：
--
作者：
Liu, Kexi;Qiao, Zhi;Wang, Guofeng
开发无铂族金属（PGM）和无铁的电催化剂是实现低成本和长期耐用的聚合物电解质膜燃料电池的必要条件。在这里，我们结合计算和实验研究来研究Mn和N共掺杂碳（表示为Mn-N- c）作为在挑战性酸性介质中氧还原反应（ORR）的有前途的催化剂的机理、活性和耐久性。第一性原理密度泛函理论计算预测，在碳层中嵌入的MnN4位点上，通过四电子途径将O-2还原为H2O是有利的。利用DFT计算的反应能，微动力学分析预测，假设催化剂中活性位点的密度相同，MnN4位点催化ORR的半波电位仅比Pt（111）低60 mV，比嵌入碳层的FeN4位点低80 mV。在计算预测的激励下，我们利用聚合物（即聚苯胺-聚苯胺）水凝胶前驱体通过高温方法合成了Mn-N-C催化剂。结构表征表明，在催化剂中很可能形成与N配位的原子分散的Mn位。电化学测试表明，合成的Mn-N-C催化剂可以促进四电子ORR，其在酸中的催化活性与用相同方法制备的Fe-N-C催化剂相当。更重要的是，Mn-N-C催化剂表现出优异的电位循环稳定性，在10000次循环后仅损失20 mV（在O-2饱和电解质中为0.6至1.0 V）。相比之下，在相同的测试条件下，Fe-N-C催化剂仅循环5000次就会损失80 mV。我们的计算和实验结果强烈表明，Mn和N共掺杂碳可能是酸性介质中ORR的高性能催化剂。
Development of platinum group metal (PGM)-free as well as iron-free electrocatalysts is imperative to achieve low-cost and long-term durability of polymer electrolyte membrane fuel cells. Here, we combined computational and experimental studies to investigate the mechanism, activity, and durability of Mn and N co-doped carbon (denoted as Mn-N-C) as promising catalysts for oxygen reduction reaction (ORR) in challenging acid medium. The first-principles density functional theory calculations predict that it is favorable for O-2 to be reduced into H2O via four-electron pathway on MnN4 sites embedded in carbon layer. Using the reaction energies calculated from DFT, microkinetic analysis predicts that the MnN4 sites could catalyze ORR with a half-wave potential only 60 mV lower than that of Pt (111) and 80 mV lower than that of the FeN4 sites embedded in carbon layer, assuming the same density of active sites in the catalysts. Motivated by the computational prediction, we synthesized a Mn-N-C catalyst using a polymer (i.e., polyaniline-PANI) hydrogel precursor via a high temperature approach. Structural characterization indicates that atomically dispersed Mn sites coordinated with N are very likely formed in the catalyst. Electrochemical measurements show that the synthesized Mn-N-C catalyst can promote four-electron ORR with a catalytic activity in acids comparable to that of the Fe-N-C catalyst prepared using the same procedure. More importantly, the Mn-N-C catalyst exhibits superior potential cyclic stability, only losing 20 mV after 10000 cycles (0.6 to 1.0 V in O-2 saturated electrolyte). In comparison, the Fe-N-C catalyst would loss 80 mV after only 5000 cycles under the same testing conditions. Our computational and experimental results strongly suggest that the Mn and N co-doped carbon could be promising high-performance catalysts for ORR in acidic medium.