Nanostructured materials
Hierarchically Structured Electrodes based on CNTs (Pei Wang)
Proton exchange membrane fuel cells (PEM-FC), which are considered as efficient and clean energy conversion devices, require chemically and mechanically stable electrodes, which should possess optimum porosity to reduce mass transfer losses, high electric conductivity to avoid Ohmic losses and large surface area to achieve enhanced current densities. In our research hierarchically structured electrodes based on carbon nanotubes (CNT) modified carbon surfaces are prepared to improve the above properties compared to typical gas diffusion electrodes prepared from Platinum/carbon powders. Moreover, the hierarchically nanostructured materials can also be utilized as super capacitor electrodes due to their large surface and high electrical conductivity.
To prepare the hierarchical electrodes, a bottom-up approach is used1. In this approach, different functionalities including graphene, primary CNT, secondary CNT and polyaniline can be assembled in a modular fashion. In the first step, electrodeposited iron nanoparticles onto glassy carbon, carbon cloth (CC) or graphene decorated CC act as a catalyst for growth of primary CNTs through chemical vapour deposition (CVD). During CVD, CNT and nitrogen-containing CNT can be produced depending on the carbon precursors such as methane, cyclohexene and acetonitrile. After primary CNT growth, a subsequent deposition of iron nanoparticles followed by a CVD step leads to branching of the CNT with secondary nanotubes. Further modification of the micro- and nanostructured electrodes were carried out by electro- or chemical deposition of polyaniline. The hierarchically structured electrodes are tested for applicability in super capacitors by evaluating the capacitance via cyclic voltammetry and charge-discharge measurements. Furthermore, the structures are employed as high surface-area electrodes for methanol oxidation after electrodepositing Platinum, meanwhile, they will be also tested as gas diffusion electrodes in fuel cell.
Modified graphene materials (Dr. Tintula Kottakat)
Development of oxygen reduction reaction (ORR) catalysts with performance comparable to Pt remains a great challenge for key renewable-energy technologies including fuel cells and metal air batteries. Towards this endower tremendous research efforts are going on metal nitrogen doped carbonaceous materials as catalyst to enhance the activity to an appreciable level. Among the various carbonaceous materials, the attractive properties of graphene in the context of catalysis such as high surface area, good chemical stability, excellent conductivity, unique graphitic basal plane structure, and flexibility in functionalization motivated us to study non-precious metal (Fe & Co) impregnated nitrogen-doped graphene as ORR catalyst. Moreover by utilizing graphene or reduced graphene oxide (rGO) significantly more nitrogen-doped surfaces sites are available for coordination with metal ions, relative to other types of carbon materials. In our study, two approaches, namely high temperature annealing and microwave methods are used for the synthesis of graphene based catalysts. The ORR activity of the prepared catalysts are determined with cyclic voltammetry and rotating disc electrode technique in alkaline electrolyte. XRD, Raman, ICP-OES and TEM analysis are used for the structural and morphological characterizations of the catalysts.
NCNTs as catalyst for an V-RFB (Mathias Kühhirt)
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