Boosting Oxygen Reduction Activity of Manganese Oxide Through Strain Effect Caused By Ion Insertion

Transition-metal oxides with a strain effect have attracted immense interest as cathode materials for fuel cells. However, owing to the introduction of heterostructures, substrates, or a large number of defects during the synthesis of strain-bearing catalysts, not only is the structure-activity relationship complicated but also their performance is mediocre. In this study, a mode of strain introduction is reported. Transition-metal ions with different electronegativities are intercalated into the cryptomelane-type manganese oxide octahedral molecular sieves (OMS-2) structure with K ions as the template, resulting in the octahedral structural distortion of MnO₆ and producing strains of different degrees. Experimental studies reveal that Ni-OMS-2 with a high compressive strain (4.12%) exhibits superior oxygen reduction performance with a half-wave potential (0.825 V vs RHE) greater than those of other reported manganese-based oxides. This result is related to the increase in the covalence of MnO₆ octahedral configuration and shifting down of the e_g band center caused by the higher compression strain. This research avoids the introduction of new chemical bonds in the main structure, weakens the effect of e_g electron filling number, and emphasizes the pure strain effect. This concept can be extended to other transition-metal-oxide catalysts.