In situ X-ray absorption spectroscopy investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction.
In situ X-ray absorption spectroscopy investigation of a bifunctional manganese oxide catalyst with high activity for electrochemical water oxidation and oxygen reduction.
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DOI：
10.1021/ja3104632
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发表时间：
2013-06-12
影响因子：
15
通讯作者：
Jaramillo, Thomas F.
中科院分区：
文献类型：
--
作者：
Gorlin, Yelena;Lassalle-Kaiser, Benedikt;Benck, Jesse D.;Gul, Sheraz;Webb, Samuel M.;Yachandra, Vittal K.;Yano, Junko;Jaramillo, Thomas F.
原位X射线吸收光谱（XAS）是一种强大的技术，可应用于电化学系统，能够阐明反应条件下电催化剂的化学性质。在这项研究中，我们进行现场XAS测量的双功能锰氧化物（MnOx）催化剂具有高的电化学活性的氧还原反应（ORR）和析氧反应（OER）。使用X射线吸收近边结构（XANES）和扩展的X射线吸收精细结构（EXAFS），我们发现，暴露于0.7 V与RHE的ORR相关的电位产生一个无序的Mn3II，III，IIIO4相与其他阶段的贡献可以忽略不计。在电势增加到相对于RHE的1.8V的高度阳极值（与OER相关）之后，我们观察到约80%的催化薄膜氧化以形成混合的MnIII、IV氧化物，而剩余的20%的膜由较少氧化的相组成，可能对应于未改变的Mn3II、III、IIIO4。XAS和电化学表征的两个薄膜催化剂具有不同的MnOx厚度显示没有显着影响的厚度上测得的氧化态，在ORR或OER电位，但表明OER活性与膜厚度的比例。该结果表明，膜具有多孔结构，其不将电催化限制在膜的顶部几何层。由于在OER所需的高电位下最有可能被氧化的催化剂膜部分是最靠近电解质界面的部分，因此我们假设MnIII、IV氧化物，而不是Mn3 II、III、IIIO 4，是与OER相关的相观察到的OER活性。
In-situ x-ray absorption spectroscopy (XAS) is a powerful technique that can be applied to electrochemical systems, with the ability to elucidate the chemical nature of electrocatalysts under reaction conditions. In this study, we perform in-situ XAS measurements on a bifunctional manganese oxide (MnOx) catalyst with high electrochemical activity for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS), we find that exposure to an ORR-relevant potential of 0.7 V vs. RHE produces a disordered Mn3II,III,IIIO4 phase with negligible contributions from other phases. After the potential is increased to a highly anodic value of 1.8 V vs. RHE, relevant to the OER, we observe an oxidation of approximately 80% of the catalytic thin film to form a mixed MnIII,IV oxide, while the remaining 20% of the film consists of a less oxidized phase, likely corresponding to unchanged Mn3II,III,IIIO4. XAS and electrochemical characterization of two thin film catalysts with different MnOx thicknesses reveals no significant influence of thickness on the measured oxidation states, at either ORR or OER potentials, but demonstrates that the OER activity scales with film thickness. This result suggests that the films have porous structure, which does not restrict electrocatalysis to the top geometric layer of the film. As the portion of the catalyst film that is most likely to be oxidized at the high potentials necessary for the OER is that which is closest to the electrolyte interface, we hypothesize that the MnIII,IV oxide, rather than Mn3II,III,IIIO4, is the phase pertinent to the observed OER activity.
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