Abstract
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 (IrO2) 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 IrO2 or the novel crystal structure. Based on two metallic pyrochlores (Bi2Ir2O7 and Pb2Ir2O6.5) and IrO2. It has been found that there exists a strong correlation between the specific OER activity and IrO6 coordination geometry. The more distortion in IrO6 geometry ascends the activity of Ir sites, and generates activity order of Pb-Ir > IrO2 > Bi-Ir. Our characterizations reveal that distorted IrO6 in Pb-Ir induces a disappearance of J = 1/2 subbands in valence band, while Bi-Ir and IrO2 resist this nature probe. The performed DFT calculations indicated the distortion in IrO6 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 IrO6 octahedral geometry through doping or utilizing structural manipulation with nature of distorted octahedral coordination.
Highlights
There is no doubt that the different properties of iridates are completely dominated by their electronic structure, which duly has strong relationship with the IrO6 coordination geometry in the oxides
In here, based on two different pyrochlore iridates (Pb2Ir2O6.5 and Bi2Ir2O7), it is illustrated that the properties of IrO6 coordination geometry in oxides play an important role in its oxygen evolution reaction (OER) activity
The morphology of Pb-Ir pyrocholre is presented by TEM image shown in Fig. 1b, they are irregular nanoparticles and size is in range of 10–40 nm
Summary
There is no doubt that the different properties of iridates are completely dominated by their electronic structure, which duly has strong relationship with the IrO6 coordination geometry in the oxides. In here, based on two different pyrochlore iridates (Pb2Ir2O6.5 and Bi2Ir2O7), it is illustrated that the properties of IrO6 coordination geometry in oxides play an important role in its OER activity. A mixture phase comprising IrO2 and Pb-Ir pyrochlore is observed in Pb-2 and Pb-3 cases where Ir is rich in oxides; it ascertains that Pb cannot substitute the Ir lattice to form the rutile structure.
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