Owing to their high energy density, lithium-oxygen batteries (LOBs) have been drawn great attention as one of the promising electrochemical energy sources. However, the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER) hamper the widespread application of LOBs. Herein, an elaborate designed catalysts which are constructed by FeN x moieties dispersed on the network-like hollow dodecahedral carbon and then decorated with Ru nanoparticles (FeN x -HDC@Ru). Since the homogeneously dispersed FeN x moieties could promote ORR performance, and the Ru nanoparticles could facilitate OER capability, the FeN x -HDC@Ru nanocomposites used as cathode catalysts can significantly improve LOBs performance. A lower discharge and charge overpotentials of 0.15 V and 0.78 V can be detected in the first cycle, respectively, and an excellent cycle performance of 90 cycles at 200 mA g −1 and 89 cycles at 500 mA g −1 can be demonstrated. Herein, the charge transfer kinetics has been enhanced with the internal network-like hollow structure and a low impedance Li 2 O 2 /catalysts contact interface could be earned by the constructed Ru nanoparticles, these factors would lead to an efficient acceleration to the formation and decomposition of Li 2 O 2 during discharge and charge process.
Platinum group metal-free catalysts based on transition metal and nitrogen co-doped carbon materials are gaining attention for their applications in electrocatalysis. Nitrogen-coordinated metal sites (MNx) have been identified as the main active sites in PGM-free catalysts. Current synthetic approaches rely on the high-temperature treatment to introduce targeted electroactive MNx sites into the carbon matrix. In this study, we demonstrated the formation of MNx sites on Ni- and N-co-doped carbon templates via the solution-phase coordination with target metal ions, including Fe2+, Fe3+, and/ Co2+. The formation of MNx sites was confirmed via a combined approach of various physical characterization techniques, elemental analysis, and electrochemical analysis. The results indicate that the metal-vacancy-Nx sites in the template can coordinate with target ions to form electrochemically active MNx sites. By varying heat-treatment temperature, the amount of FeNx sites formed via coordination with Fe2+ ion can be tuned and correlated with the change of activity toward oxygen reduction reaction. The amount of MNx sites formed via solution-phase coordination with various ions followed the sequence of Co2+ > Fe2+ > Fe3+. These findings may further guide the future development of MNx-C electrocatalysts through this solution-phase coordination approach.
Lingwu Meng,Maosheng Lin,Qirui Guo,Longzhao Zhang,Xiangyu Huang,Shule Zhang,Weihua Ma
Stabilizing metal species at the atomic level and tuning their catalytic properties is a significant challenge. Herein, an N-doped Fe x O y -N-ZSM-5 catalyst with layered and chain-like graphene structures is reported. The catalyst can selectively catalyze the oxidation of triethylamine (TEA) with an efficiency of 99.7 % at 240 °C, and maintain an N 2 yield of 97.6 % over the reaction temperature range of 240–360 °C. The results indicate that the layered graphene in the catalyst provide anchor sites for active Fe, while the abundant chain-like graphene act as connectors between ZSM-5 and the layered graphene, offering ample opportunities for TEA and its intermediates to contact the catalyst surface. This increases the number of active sites on the catalyst, thereby enhancing the catalytic performance of Fe x O y -N-ZSM-5. Notably, due to the interaction between FeO x and FeN x species, Fe x O y -N-ZSM-5 exhibits excellent thermal stability and water resistance, demonstrating promising potential for practical.
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