Kyoung Hwan Choi

Proton conduction in AIII0.5BV0.5P2O7 compounds at intermediate temperatures

Proton conductors capable of operation between 100 and 400 °C are attractive electrochemical materials due to their high utility value in energy and environmental applications. However, such proton conductors have not yet made headway in the marketplace, due to insufficient proton conductivity. Here, we present new types of metal pyrophosphates as promising candidates for intermediate temperature proton conductors. A series of AIII0.5BV0.5P2O7 (AIIIBV = InSb, SbSb, FeSb, GaNb, FeNb, YNb, GaTa, AlTa, FeTa, YTa, BiTa, and SmTa) compounds were synthesized, of which In0.5Sb0.5P2O7, Fe0.5Nb0.5P2O7, and Fe0.5Ta0.5P2O7 exhibited the highest proton conductivities in the temperature ranges of 50–100 °C (0.045 S cm−1@100 °C), 100–200 °C (0.12 S cm−1@150 °C), and 200–400 °C (0.18 S cm−1@250 °C), respectively, in unhumidified air. The proton conductivity of these three compounds was further enhanced by the introduction of AIII or BV deficiency into the bulk. Consequently, Fe0.4Ta0.5P2O7 exhibited the highest proton conductivity of 0.27 S cm−1 at 300 °C in unhumidified air. Such high proton conductivity values were also observed under fuel cell operating conditions. The environments of protons in the bulk of these compounds were monitored using Fourier transform infrared (FT-IR) spectroscopy, temperature-programmed desorption (TPD), and proton magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Protons were incorporated into the compounds for charge-compensation of the deficient AIII or BV cations, which results in an increase in the quantity of protons. More importantly, the mobility of the protons was also enhanced. Various electrochemical measurements demonstrate that proton conduction is dominant in these compounds, where the protons migrate according to a hopping mechanism.

Measuring Methanol Concentrations in a Vapor-Fed Direct Methanol Fuel Cell Using Laser Absorption Spectroscopy

Gas-phase absorption spectroscopy using a 3.39 μm He-Ne laser enables the concentration of methanol vapor in a vapor-fed direct methanol fuel cell (DMFC) to be measured in real-time and in situ once high noise levels of the laser are corrected. The changes that methanol vapor concentrations bring to cell performance can be measured under various galvanostatic and potentiostatic conditions and analyzed with regard to methanol crossover and methanol transport capability. The absorption coefficient of +methanol vapor, 0.005336 cm -1 Torr -1 , is nearly constant under the DMFC operating conditions at a wavelength of 3.39 μm.

High Performance Membrane Electrode Assemblies by Optimization of Processes and Supported Catalysts

© 2012 Pak et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. High Performance Membrane Electrode Assemblies by Optimization of Processes and Supported Catalysts