Surface structure optimization by selective dissolution to improve the oxygen reduction performance of SmMn2O5

Abstract

Selective dissolution is an effective strategy to improve the catalytic performance. This method was used to regulate the surface structure of SmMn₂O₅ through HNO₃ acidification to promote its oxygen reduction reaction (ORR) performance. The relationship between the structures and ORR performances of SmMn₂O₅ acidified by different concentrations of HNO₃ (5-8 M) was investigated. HNO₃ can selectively dissolve part of Sm, which reduces Sm/Mn ratio, and increases Mn⁴⁺/Mn³⁺ and surface adsorbed oxygen/lattice oxygen ratios on the catalyst surface. Especially, the increase of Mn⁴⁺ content optimizes the adsorption of oxygen-containing intermediates on Mn³⁺ active sites and enhances the ORR activity. When treated with 7 M HNO₃ for 10 h, the acidified SmMn₂O₅ surface has suitable Mn⁴⁺/Mn³⁺ ratio, exhibiting excellent ORR performance. Compared with SmMn₂O₅, the half-wave potential of the acidified SmMn₂O₅ increases from 0.80 V to 0.83 V, and the diffusion-limited current density improves from 3.44 mA·cm⁻² to 4.76 mA·cm⁻². Additionally, the synergistic catalytic mechanism of Mn⁴⁺ with Mn³⁺ active sites was well discussed.