Oxygen reduction reaction (ORR) is essential for the electrochemical energy conversion devices such as Zn-air and fuel cells. it is kinetically so sluggish that precious metal-based electrocatalysts have been employed, which increases the price of system. A variety of non-precious metal-based ORR catalysts have been studied, and among them, M-N-C type electrocatalysts are most promising in terms of catalytic performances. In this work, atomically dispersed M-N-C type catalysts were prepared for the application to rechargeable Zn-air batteries.
Ti-introduced thermally exfoliated graphene oxide (Ti-TEGO) was used for the preparation of atomically dispersed bimetallic catalysts. After supporting FePc followed by activating at high temperature, Fe-Ti bimetallic atomic catalysts were produced. Prepared bimetallic catalysts revealed different catalytic performances depending on the contents of Ti and the condition of activation (the duration of activation, the activation temperature and the composition of activation gas). The best performed catalyst, Fe/TEGO-Ti-0.5-950 (0.5 wt% Ti and activated for 2.5 min at 950℃ under the stream of NH3), showed 2.3 times higher ORR performance than a commercial Pt/C. Furthermore, the rechargeable Zn-air battery employed Fe/TEGO-Ti-0.5-950 as a cathode catalyst delivered the better performance than that employed Pt/C.
Fe single atom catalysts were prepared using 1,8-diamminonaphthalene, FeCl2, and colloidal silica as a carbon precursor, metal source, and a template, respectively. Depending on the preparation conditions such as the type of silica, the contents of silica, and activation temperature, prepared catalysts showed different morphology and catalytic properties. It was found that the interaction between carbon precursor and silica template would be important for the generation of single atom and dispersion of active site. Among the catalysts examined, FDAN-Si(Cl, 30%) 50% NH3-AT-NH3 showed best catalytic performance in both the half-cell experiment and rechargeable Zn-air battery.
Recently, silicon is attracting attention as an anode material for lithium ion batteries. Silicon has the advantage of having a theoretical capacity 10 times better than that of commercial graphite. However, the formation of unstable SEI layer, which results from large change in volume during the insertion and deinsertion process of lithium ions, makes it difficult for the application as an anode. In this study, dopamine-derived carbon and TiN double layers were introduced on the silicon surface to suppress volume change and improve the cycle stability. After forming a polydopamine shell on Si, a TiO2 shell was introduced through a surface reaction between function groups on polydopamine and Ti precursor. Various types of Si-based anode materials with the core-shell structure were prepared under varied preparation conditions. Among the samples studied, Si-C-TiN (N2, NH3), which was prepared by a successive heat-treatment under N2 followed by NH3, showed the highest Li capacity and the best cycling stability. The TiN layers formed on the surface of carbon in Si-C core-shell was responsible for the enhanced cycling stability of Si-C-TiN (N2, NH3).