Regulating the Oxygen Affinity of Single Atom Catalysts by Dual-atom Design for Enhanced Oxygen Reduction Reaction Activity

This work chooses Cu/Fe single-atom catalysts(SACs)with weak/strong oxygen affinity to clarify the effect of dual-atom configuration on oxygen reduction reaction(ORR)performance based on density functional theory(DFT)calculations.The stability and ORR activity of single or dual Cu/Fe atomic sites anchored on nitrogen-doped graphene sheets(Cu-N4-C,Cu2-N_(6)-C,Fe-N4-C,and Fe_(2)-N_(6)-C)are investigated,and the results indicate the dual-atom catalysts(Cu2-N_(6)-C and Fe_(2)-N_(6)-C)are thermodynamically stable enough to avoid sintering and aggregation.Compared with single-atom active sites of Cu-N4-C,which show weak oxygen affinity and poor ORR performance with a limiting potential of 0.58 V,the dual-Cu active sites of Cu2-N_(6)-C exhibit enhanced ORR activity with a limiting potential up to 0.87 V due to strengthened oxygen affinity.Interestingly,for Fe SACs with strong oxygen affinity,the DFT results show that the dual-Fe sites stabilize the two OH*ligands structure[Fe_(2)(OH)2-N_(6)-C],which act as the active sites during ORR process,resulting in greatly improved ORR performance with a limiting potential of 0.90 V.This study suggests that the dual-atom design is a potential strategy to improve the ORR performance of SACs,in which the activity of the single atom active sites is limited with weak or strong oxygen affinity.

High-temperature ferromagnetic metallic phase in LaMnO_(3)/Sr_(3)Al_(2)O_(6)heterostructure

To achieve a flexible single-crystal multifunctional membrane,the freestanding process of a rigid epitaxial transition metal oxide thin film via a buffered water-dissolution sacrificial layer has attracted reasonable attentions.Owing to the difference in chemical potential,specific element affinity,and lattice constant between the target membrane and the sacrificial layer,the freestanding process may cause an indelible change of physics property once the target thin film is sensitive to the above factors.Here,the heterostructures composed of the generally adopted sacrificial layer Sr_(3)Al_(2)O_(6)(SAO)and LaMnO_(3)(LMO)have been systematically investigated.The electrical and magnetic properties of LMO show extreme sensitivity to the thickness of SAO(tSAO).Then we have also found that LMO/SAO heterostructures can exhibit the coexistence of two ferromagnetic phases,the significantly enhanced Curie temperature~342 K,and the large magnetoresistance-23.3%at 300 K,which is similar to the optimal-doped manganite such as La_(2/3)Sr_(1/3)MnO_(3).X-ray diffraction results show that continuously tunable strain from out-of-plane tension to relaxation and then to compression can be generated by adjusting tSAO.This strain can stabilize the migrated oxygen from LMO to SAO,which is induced by the large oxygen affinity difference between Bsite Mn and Al.It is believed that these unexpected electrical/magnetic phenomena are originated from the combined effects of interfacial element diffusion and strain.Our study provides a strategy for designing new magnetic phases,and a reference for the fundamental understanding of strongly correlated transition metal oxide systems in the freestanding process.