Different Carbide Derived Nanoporous Carbon Supports and Electroreduction of Oxygen
Authors: Härk Eneli , Russina Margarita , Kardjilov Nikolay , Manke Ingo , Hilger André , Jäger Rutha , Tallo Indrek , Thomberg Thomas , Kurig Heisi , Lust Enn 
Published: February 2020

It has been recognized that, depending on the heat-treatment temperatures different carbon materials exhibit different properties, such as the surface area, porosity, electrical and ionic conductivity, water uptake as well as the electrocatalytic activity. During last ten years various carbides have been used as a raw material for synthesis of the nanoporous carbons with exact pore size distribution.
The main aim of this work was to investigate influence of the synthesis temperature on the various physical and electrochemical properties of nanoporous carbons, prepared from SiC, TiC, Mo2C using chlorination process at various temperatures from 600°C to 1000°C.
The X-ray microtomography, X-ray diffraction, Raman spectroscopy, time-of-flight mass spectrometry, scanning electron microscopy and transmission electron methods were applied for the structural and electronic characterization of materials. Due to the different precursor carbide and chlorination temperature used, the synthesized carbons have very different morphology, i.e. mainly amorphous or partly amorphous with well-defined graphitic areas. According to the gas adsorption data measured at liquid nitrogen temperature the specific surface area of precursor carbide increase in the following order: SiC < Mo2C ≤ TiC. The total pore volume value for Mo2C is two and three times higher compared with TiC and SiC, respectively.
The chemical contamination of carbon powders has been identified by the X-ray microtomography. It has been established that, the amount of contaminants in carbon powders depends strongly on the synthesis method and chlorination temperature used. The X-ray microtomography images also demonstrate that the carbon nanoparticles are partly agglomerated. The carbons with the fine particle sizes (C(TiC) and C(Mo2C)) more easily form agglomerates with various sizes, than (C(SiC)) carbon with coarse particles.
The results established for carbide derived carbon (CDC) powders have been compared with commercially available ordered mesoporous carbon CMK-3 (ACS Material).
Electrocatalytic activity of electrodes prepared from CDC powders has been studied by the rotating disc electrode, cyclic voltammetry and electrochemical impedance methods. Electrochemical data for nanoporous carbon electrodes show that the catalytic activity and mechanism noticeable depends on the hierarchical structure of the carbon electrode mainly, on the micro-mesoporosity and specific surface area of electrode under study.
The partially graphitized carbon C(Mo2C) with a large number of edge plane sites showed higher electrocatalytic activity towards oxygen reduction compared with amorphous carbons studied.
The calculated capacitance values in the electrical double layer region for the C(Mo2C) electrode are nearly eight times higher than those for C(TiC). Within oxygen (as well as surfake oxide) electroreduction and hydrogen evolution region, very high faradaic pseudocapacitance value have been calculated, demonstrating that C(Mo2C) electrodes can be used in hybride energy storage/generation devices.

Acknowledgements: This work was supported by the European Spallation Source Project: Estonian Partition in ESS Instrument design, development and building and application for scientific research: SLOKT12026T; the Estonian target research: IUT20-13; the Estonian Centre of Excellence in Science: TK117T "High-technology Materials for Sustainable Development"; the Estonian Energy Technology Program: SLOKT10209T and the Materials Technology Project: SLOKT12180T.

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