Enhanced stability of symmetrical polymer electrolyte membrane fuel cell single cells based on novel hierarchical microporous-mesoporous carbon supports

Fuel cell electrodes were prepared from Pt nanocluster activated hierarchical microporous-mesoporous carbon powders. The carbon supports were synthesized from molybdenum carbide applying the high-temperature chlorination method. Six different synthesis temperatures within the range from 600 to 1000 °C were used for preparation of carbon supports. Thermogravimetric analysis, X-ray diffraction, low-temperature nitrogen sorption, and high-resolution scanning electron microscopy methods were used to characterize the structure of the electrode materials and symmetrical membrane electrode assemblies (MEAs). The MEAs prepared were used to conduct the proton exchange membrane fuel cell (PEMFC)single-cell measurements. The polarization and power density curves for single cells were calculated to evaluate the activity of the catalyst materials synthesized. The electrochemically active surface area (from 2.4 to 11.9 m² g^?1) was obtained in order to estimate the contact surface areas of platinum and Nafion® electrolyte. The values of the electrolyte resistance, polarization resistance, and cell degradation rate were calculated from electrochemical impedance spectroscopy data. The carbon materials synthesized within temperature range from 600 to 850 °C were found to be the most suitable supports for PEMFCs, having higher maximum power density values and better stability (cell potential degradation 240 μV h^?1) than commercial carbon-based (Vulcan XC72; 670 μV h^?1) single cells.     

Supercapacitors based on carbide-derived carbons synthesised using HCl and Cl2 as reactants

Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder via a gas-phase reaction using HCl and Cl₂ within the temperature range of 700–1,100 °C. Analysis of X-ray diffraction results show that TiC-CDCs consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1,577 cm^?1 and the disorder-induced peaks at ~1,338 cm^?1. The low-temperature N₂ sorption experiments were performed, and specific surface areas up to 1,214 and 1,544 m²?g^?1 were obtained for TiC-CDC (HCl) synthesised at T?=?800 °C and TiC-CDC (Cl₂) synthesised at T?=?900 °C, respectively. For the TiC-CDC powders synthesised, a bimodal pore size distribution has been established with the first maximum in the region up to 1.5 nm and the second maximum from 2 to 4 nm. The energy-related properties of supercapacitors based on 1 M (C₂H₅)₃CH₃NBF₄ in acetonitrile and TiC-CDC (Cl₂) and TiC-CDC (HCl) as electrode materials were also investigated by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The specific energy, calculated at U?=?3.0 V, are maximal for TiC-CDC (Cl₂ 800 °C) and TiC-CDC (HCl 900 °C), which are 43.1 and 31.1 W?h?kg^?1, respectively. The specific power, calculated at cell potential U?=?3.0 V, are maximal for TiC-CDC (Cl₂ 1,000 °C) and TiC-CDC (HCl 1,000 °C), which are 805.2 and 847.5 kW?kg^?1, respectively. The Ragone plots for CDCs prepared by using Cl₂ or HCl are quite similar, and at high power loads, the TiC-CDC material synthesised using Cl₂ at 900 °C, i.e. the material with optimal pore structure, delivers the highest power at constant energy.