Danyu Wang

The pursuit of advanced battery chemistries with enhanced energy density necessitates the exploration of new materials, a process intricately tied to synthesis science. Despite the promise of O3-type sodium oxygen anionic redox cathodes as high-capacity materials, their development has been severely hindered by a lack of understanding regarding synthetic mechanisms. Here, we elucidate the pivotal role of atmospheric conditions, particularly oxygen content, in the synthesis of such materials by synchronizing multiple operando characterization techniques to monitor changes in both solid and gaseous components. Utilizing the O3-Na[Li_1/3Mn_2/3]O₂ system as a model, we demonstrate that a low oxygen environment is essential and the reaction is highly complex as evidenced by multiple oxygen uptake and release processes, resulting in numerous intermediates. This behavior contrasts sharply with Na-Mn-O and Li-Mn-O ternary systems which show less significant oxygen dynamics, underscoring the unique reaction mechanism within the Na-Li-Mn-O system. We further adopt a dynamic controlled atmosphere approach to modulate oxygen concentration and demonstrate successful synthesis of Ti-substituted NaLi_1/3Mn_2/3-xTi_xO₂ materials, all exhibiting capacities surpassing 190 mAh g^-1. Our findings highlight the importance of the atmospheric conditions for the synthesis of oxide cathode materials and these fundamental insights unlock avenues for developing novel high-energy-density sodium-ion battery chemistries.

The synergistic relationship between platinum (Pt) and ceria support is vital for advancing the innovative design of Pt/ceria catalyst, which extensively applied in the fields of energy conversion and environmental remediation. Through thermal treatment, A serial of Pt/ceria with different metal support interaction were obtained. Advanced analyses employing in situ transmission electron microscopy (TEM) and X-ray Photon-electron Spectroscopy (XPS) elucidated that these thermal methods provoke a marked affinity between the Pt clusters and ceria support. High-temperature treatment can result in partial encapsulation of Pt clusters by CeO2, enabling the Pt clusters to match to the CeO2 lattice. Notably, high-temperature treatments lead to the partial encapsulation of Pt clusters by CeO2, facilitating alignment of the Pt clusters with the CeO2 lattice. This results in the emergence of oxidized Pt (Pt4+), which replaces the initial metallic Pt0, embedding itself onto the ceria support and subsequently activating adjacent Ce atoms in proximity to Pt. This innovative structure creates more site for CO adsorption but with weaker adsorption energy, effectively eliminating CO poisoning on the Pt surface and enhancing O2 dissociative adsorption. Collectively, these modifications birth a catalyst exhibiting remarkable proficiency in low-temperature CO oxidation.

The La₂O₃ catalyst exhibits good performance in OCM reactions for its promising C₂ selectivity and yield. Previous studies have affirmed that the formation of carbonates in La₂O₃ impedes the catalyst’s activity as a result of poisoning from CO₂ exposure. In this study, a series of Na₂WO₄-impregnated La₂O₃ catalysts were synthesized to investigate the poisoning-resistant effect. The bulk phase and kinetics of the catalysts were analyzed in reactors employed with in situ XRD-MS and online MS, focusing on the CO₂ adsorption on La₂O₃ and the phase transition process to La₂O₂CO₃ in temperature zone correlated to OCM light-off. In situ XRD analysis revealed that, with Na₂WO₄ doped, CO₂ exposure at elevated temperatures formed La₂O₂CO₃ in tetragonal crystal phases, exhibiting distinctive differences from the hexagonal phase carbonates in undoped commercial La₂O₃. The ability to develop tetragonal or monoclinic La₂O₂CO₃ was suggested as a descriptor to assess the sensitivity of La₂O₃ catalysts to CO₂ adsorption, a tunable characteristic found in this study through varying Na₂WO₄ doping levels. Coupled XRD-MS analysis of CO₂ adsorption uptake and phase change further confirmed a positive dependence between the resistivity of La₂O₃ catalyst to CO₂ adsorption and its low-temperature C₂ selectivity. The results extended the previous CO₂ poisoning effect from multiple perspectives, offering a novel modification approach for enhancing the low-temperature performance of La₂O₃ catalysts in OCM.