Hydrocarbons are the major source for the production of hydrogen gas, by, for instance, reforming of fossil fuel, natural gas, or biomass. However, the hydrogen produced by this process is not pure, but a mixture of gases known as reformate.
Hydrogen, nitrogen, water, carbon monoxide and carbon dioxide are the typical gases in the mixture. Other impurities, including NH3, H2S, and hydrocarbons are also present in the mixture. Some of these contaminants have little or no effect on the catalyst of the fuel cell, while others are highly poisonous.
It is essential to understand the effect of these contaminants on the performance of a fuel cell for optimizing the purification procedure. The combination of mass spectrometry and electrochemical techniques like electrochemical impedance spectroscopy, stripping cyclic voltammetry, potentiostatic and galvanostatic experiments aids in gaining insights into the reason behind the impact of impurities on the cell performance. The cell housing is depicted in Figure 1.
Figure 1. Cell housing
Experimental Procedure and Results
The top image in Figure 2a depicts three different CVs using ethene as an example: a base CV, collected in inert gas, a CV collected in a continuous flow of 100ppm ethene contaminated argon, and a stripping CV. The stripping CV is recorded after exposing the electrode to ethene contaminated argon for some time and then purging the system. It is possible to interpret the origin of the variations between the different CVs using mass spectrometry.
A Hiden (HPR-20 QIC) Mass Spectrometer and a PAR 273A potentiostat were used to perform the measurements. The bottom image in Figure 2a depicts the /z = 44 signal, which is a result of carbon dioxide. This corresponds with the oxidation peaks at 0.6V (30s and 145 in the continuous case), revealing the oxidation of the adspecies arising from ethane to carbon dioxide at potentials > 0.35 V vs RHE.
Figure 2b shows the signals m/z = 15 and 30, which can be observed around the hydrogen evolution peak. This indicates that methane and ethane are formed at these low potentials. The amount of adspecies generated on the surface of the catalyst was found to be less when hydrogen was present in the gaseous phase or adsorbed on the surface in the ethane contaminated gas. This means that the performance of PEM fuel cell is less affected by the traces of ethene present in the hydrogen feed.
Figure 2. Cyclic Voltammograms recorded in a fuel cell at 80°C and 90%RH, at a scan rate of 10mVs-1 and selected m/z signals. Colour codes: CVs recorded in pure argon (grey), 100ppm ethene/argon (blue), stripping CV (red) after 10min adsorption of 100ppm ethene at 0.3 V and. All three signals in b) bottom are recorded in 100ppm ethene/argon.
Project Summary by: Maohong Fan Department of Chemical & Petroleum Engineering, University of Wyoming, Laramie, WY 82071, USA
Paper Reference: L. Xu et al. (2014) “Catalytic CH4 reforming with CO2 over activated carbon based catalysts” Applied Catalysis A: General 469, 387-397
Hiden Product: HPR-20 QIC R&D
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