Surface engineering on MnO_(2)nanorods by La single atoms to accelerate oxygen reduction kinetics

Surface engineering,which modulates the electronic structure and adsorption/desorption properties of electrocatalysts,is one of the key strategies for improving the catalytic performance.Herein,we demonstrate a facile solid-phase reaction for surface engineering of MnO_(2)to boost the oxygen reduction kinetics.Via reaction with surface hydroxy groups,La single atoms with loading amount up to 2.7 wt%are anchored onto a-MnO_(2)nanorods.After surface engineering,the oxygen reduction reaction(ORR)kinetics is significantly improved with the half-wave potential from 0.70 to 0.84 V,the number of transferred electrons from 2.5 to 3.9 and the limiting current density from 4.8 to 6.0 mA·cm^(-2).In addition,the catalyst delivers superior discharge performance in both alkaline and neutral metal–air batteries.Density functional theory(DFT)calculations reveal that atomic La modulates the surface electronic configuration of MnO_(2),reduces its d-band center and thus lowers the OOH*and O*reaction energy barrier.This work provides a new route for rational design of highly active electrocatalyst and holds great potential for application in various catalytic reactions.

Insight into structural degradation of NCMs under extreme fast charging process

Lithium-ion batteries(LIBs)with extreme fast charging(XFC)capability are considered an effective way to alleviate range anxiety for electric vehicle(EV)buyers.Owing to the high ionic and electronic conductivity of LiNi_(x)Co_(y)Mn_zO_(2)(x+y+z=1,NCM)cathodes,the inevitable Li plating of graphite in NCM|graphite cell is usually identified as a key bottleneck for XFC LIBs.However,the capacity decay mechanism of cathode materials under XFC has not been fully investigated.In this work,three typical NCM cathode materials with different Ni fractions were chosen and their electrochemical performances under XFC associated with structural evolution were investigated.A faster capacity decay of NCMs under XFC conditions is observed,especially for Ni-rich NCMs.In-situ X-ray diffraction(XRD)reveals that the multiple caxis parameters appear at the high-voltage regions in Nirich NCMs,which is probably triggered by the larger obstruction of Li(de)intercalation.Particularly,NCMs with moderate Ni fraction also present a similar trend under XFC conditions.This phenomenon is more detrimental to the structural and morphological stability,resulting in a faster capacity decay than that under low current charging.This work provides new insight into the degradation mechanism of NCMs under XFC conditions,which can promote the development of NCM cathode materials with XFC capability.