Experimental and Theoretical Investigation of the Effect of Oxygen Vacancies on the Electronic Structure and Pseudocapacitance of MnO₂

Abstract

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Influence of the MnO2 Phase on Oxygen Evolution Reaction Performance for Low‐Loading Iridium Electrocatalysts

“…As shown in Figure 4(a), the Mn2p3/2 spectrum was deconvoluted into two peaks at 641.1 eV and 642.3 eV, while the Mn2p1/2 spectrum could be fitted into two peaks at 652.7 eV and 653.8 eV. The peaks at 641.1 eV and 652.7 eV are attributed to Mn 3+ ; while the peaks at 642.3 eV and 653.8 eV are attributed to Mn 4+ [22] . From the Mn2p spectrum the ratios of Mn 3+ /Mn 4+ were calculated and summarized in Table 1.…”

“…These results indicated that the samples had a mixed valence state. Meanwhile, the Mn2p spectrum was used to estimate proportions of manganese in different valence states [22] . As shown in Figure 4(a), the Mn2p3/2 spectrum was deconvoluted into two peaks at 641.1 eV and 642.3 eV, while the Mn2p1/2 spectrum could be fitted into two peaks at 652.7 eV and 653.8 eV.…”

“…From Table 1, it could be found that the content of lattice oxygen increased as follow : IrO 2 /α‐ MnO 2 <IrO 2 /δ‐MnO 2 <IrO 2 /γ‐MnO 2 <IrO 2 /β‐MnO 2 . Low lattice oxygen content was helpful for conductivity and would increase the activity of iridium [22,25] . But the surface adsorbed oxygen content changed as follow: IrO 2 /α‐MnO 2 >IrO 2 /δ‐MnO 2 >IrO 2 /γ‐MnO 2 >IrO 2 /β‐MnO 2.…”

“…But the surface adsorbed oxygen content changed as follow: IrO 2 /α‐MnO 2 >IrO 2 /δ‐MnO 2 >IrO 2 /γ‐MnO 2 >IrO 2 /β‐MnO 2. With the increase of the surface adsorbed oxygen content, higher surface reactivity or more active sites would be achieved [22] . Therefore, it could be expected that IrO 2 /α‐MnO 2 would have a better activity.…”

“…In addition, the presence of Mn 3+ ions could also promote the OER activities because the Mn 3+ in the MnO 2 provides t 2g 3 e g 1 structure, which result in degenerated e g orbitals asymmetrically filled in high‐spin state [33] . The high spin state with e g 1 in the Mn could be oriented toward the OH − group, which finally enhanced the OER activity [12a,22] …”