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

Selective dissolution is an effective strategy to improve the catalytic performance. This method was used to regulate the surface structure of SmMn 2 O 5 through HNO 3 acidification to promote its oxygen reduction reaction (ORR) performance. The relationship between the structures and ORR performances of SmMn 2 O 5 acidified by different concentrations of HNO 3 (5-8 M) was investigated. HNO 3 can selectively dissolve part of Sm, which reduces Sm/Mn ratio, and increases Mn 4+ /Mn 3+ and surface adsorbed oxygen/lattice oxygen ratios on the catalyst surface. Especially, the increase of Mn 4+ content optimizes the adsorption of oxygen-containing intermediates on Mn 3+ active sites and enhances the ORR activity. When treated with 7 M HNO 3 for 10 h, the acidified SmMn 2 O 5 surface has suitable Mn 4+ /Mn 3+ ratio, exhibiting excellent ORR performance. Compared with SmMn 2 O 5 , the half-wave potential of the acidified SmMn 2 O 5 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 Mn 4+ with Mn 3+ active sites was well discussed.