Unveiling the mechanism of charge compensation in Li_(2)Ru_(x)Mn_(1-x)O_(3)by tracking atomic structural evolution

The relationship between the structural evolution and redox of Li-rich transition-metal layered oxides(LLOs)cathodes remains ambiguous,obstructing the development of high-performance lithium-ion(Li^(+))battery.Herein,the coherent effects of local atomic and electronic structure in Li_(2)Ru_(x)Mn_(1-x)O_(3)(LRMO)with a wide voltage window(1.3–4.8 V)is identified by in situ X-ray absorption fine spectroscopy(XAFS)and chemometrics.We not only skillfully separated the redox active structures to track the electrochemical path,but also visualized the coupling mechanism between the evolution of Ru-Ru dimer and the(de)excitation of cations and anions.Furthermore,introducing manganese triggers the“heterogeneity”of coordination environment and electronic structure between Ru and Mn after discharge to 3 V.The change of thermodynamic and kinetic paths affects the relithiation,and further leads to the hysteresis of the anion activation structure relaxation of Li_(2)Ru_(0.4)Mn_(0.6)O_(3)relative to Li_(2)RuO_(3)(LRO).Additionally,it is demonstrated that the high charge cut-off voltage restrains the relaxation of anionic active structure in LRO from a new perspective through comparative experiments.Our work associates the evolution of atomic structure with charge compensation and negative electrochemical reactions such as voltage hysteresis(VH)and capacity attenuation,deepening the understanding electrochemical reaction mechanism of LLOs during the first cycle and providing a theoretical support for the further design and synthesis of high-efficiency cathodes.

CeO_(2) doping boosted low-temperature NH3-SCR activity of FeTiOx catalyst:A microstructure analysis and reaction mechanistic study

FeTiOx has been recognized as an environmental-friendly and cost-effective catalyst for selective catalytic reduction(SCR)of NOx with NH3.Aimed at further improving the low-temperature DeNOx efficiency of FeTiOx catalyst,a simple strategy of CeO_(2) doping was proposed.The low-temperature(<250°C)NH3-SCR activity of FeTiOx catalyst could be dramatically enhanced by CeO2 doping,and the optimal composition of the catalyst was confirmed as FeCe_(0.2)TiOx,which performed a NOx conversion of 90%at ca.200°C.According to X-ray diffraction(XRD),Raman spectra and X-ray absorption fine structure spectroscopy(XAFS)analysis,FeCe_(0.2)TiOx showed low crystallinity,with Fe and Ce species well mixed with each other.Based on the fitting results of extended X-ray absorption fine structure(EXAFS),a unique Ce-O-Fe structure was formed in FeCe_(0.2)TiOx catalyst.The well improved specific surface area and the newly formed Ce-O-Fe structure dramatically contributed to the improvement of the redox property of FeCe_(0.2)TiOx catalyst,which was well confirmed by H2-temperature-programmed reduction(H2-TPR)and in situ XAFS experiments.Such enhanced redox capability could benefit the activation of NO and NH_(3) at low temperatures for NOx removal.The detailed reaction mechanism study further suggested that the facile oxidative dehydrogenation of NH_(3) to highly reactive-NH_(2) played a key role in enhancing the low-temperature NH_(3)-SCR performance of FeCe_(0.2)TiOx catalyst.