Li Qihao, Pollock Christopher J, Soto Joesene, Villarino Andrés Molina, Shi Zixiao, Krumov Mihail R, Muller David A, Abruña Héctor D
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853, USA.
Cornell High Energy Synchrotron Source, Wilson Laboratory, Cornell University, Ithaca, NY, 14853, USA.
Nat Commun. 2025 Mar 27;16(1):3008. doi: 10.1038/s41467-025-57177-y.
Capturing the active state of (electro)catalysts under operating conditions, namely operando, is the ultimate objective of (electro)catalyst characterization, enabling the unraveling of reaction mechanisms and advancing (electro)catalyst development. Operando insights advance our understanding of the correlations between electrochemical tests and device-level performances. However, operando characterization of electrocatalysts is challenging due to the complexity of electrochemical devices and instrumental limitations. As a result, the majority of electrocatalyst characterizations have been limited to half-cell in situ studies. Here, we present an operando X-ray absorption spectroscopic study of Mn spinel oxide electrocatalysts in an operating fuel cell employing a custom-designed cell. Our results reveal that in anion exchange membrane fuel cells, the Mn valence state, within spinel MnO/C, increases to above 3+, adopting an octahedral coordination devoid of Jahn-Teller distortions. This structural change results in an AEMFC performance equivalent to that of CoMnO/C, a composition that outperforms MnO/C in rotating disk electrode tests. Our results underscore the importance of operando characterizations in elucidating the active state of electrocatalysts and understanding the correlation(s) between electrochemical tests and device performance.
在操作条件下，即原位条件下捕获（电）催化剂的活性状态，是（电）催化剂表征的最终目标，有助于揭示反应机理并推动（电）催化剂的发展。原位研究结果有助于我们理解电化学测试与器件级性能之间的相关性。然而，由于电化学装置的复杂性和仪器的局限性，对电催化剂进行原位表征具有挑战性。因此，大多数电催化剂表征仅限于半电池原位研究。在此，我们展示了一项在使用定制设计电池的运行燃料电池中对锰尖晶石氧化物电催化剂进行的原位X射线吸收光谱研究。我们的结果表明，在阴离子交换膜燃料电池中，尖晶石MnO/C内的锰价态增加到3 +以上，采用八面体配位且无 Jahn-Teller 畸变。这种结构变化导致阴离子交换膜燃料电池的性能与CoMnO/C相当，在旋转圆盘电极测试中，CoMnO/C的性能优于MnO/C。我们的结果强调了原位表征在阐明电催化剂活性状态以及理解电化学测试与器件性能之间相关性方面的重要性。
