OER activity manipulated by IrO6 coordination geometry: an insight from pyrochlore iridates

• Published in: Scientific reports Vol. 6; no. 1; p. 38429
• Main Authors: Sun, Wei, Liu, Ji-Yuan, Gong, Xue-Qing, Zaman, Waqas-Qamar, Cao, Li-Mei, Yang, Ji
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 02.12.2016; Nature Publishing Group
• Subjects: 140/146; 639/638/161/886; 639/638/77/886; Crystal structure; Electrochemistry; Electrolysis; Geometry; Humanities and Social Sciences; Interfaces; Iridium; Lead; multidisciplinary; Oxides; Science
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep38429

The anodic reaction of oxygen evolution reaction (OER), an important point for electrolysis, however, remains the obstacle due to its complicated reaction at electrochemical interfaces. Iridium oxide (IrO 2 ) is the only currently known 5d transition metal oxide possessing admirable OER activity. Tremendous efforts have been carried out to enhance the activity of iridium oxides. Unfortunately there lies a gap in understanding what factors responsible for the activity in doped IrO 2 or the novel crystal structure. Based on two metallic pyrochlores (Bi 2 Ir 2 O 7 and Pb 2 Ir 2 O 6.5 ) and IrO 2 . It has been found that there exists a strong correlation between the specific OER activity and IrO 6 coordination geometry. The more distortion in IrO 6 geometry ascends the activity of Ir sites, and generates activity order of Pb-Ir > IrO 2  > Bi-Ir. Our characterizations reveal that distorted IrO 6 in Pb-Ir induces a disappearance of J = 1/2 subbands in valence band, while Bi-Ir and IrO 2 resist this nature probe. The performed DFT calculations indicated the distortion in IrO 6 geometry can optimize binding strength between Ir-5d and O-2p due to broader d band width. Based on this insight, enhancement in OER activity is obtained by effects that change IrO 6 octahedral geometry through doping or utilizing structural manipulation with nature of distorted octahedral coordination.