Performance of a low temperature polymer electrolyte membrane fuel cell (PEMFC) is highly dependent on the kind of catalysts, catalyst supports, ionomer amount on the catalyst layers (CL), membrane types and operating conditions. In this work, we investigated the influence of membrane types and CL compositions on MEA performance. MEA performance increases under all practically relevant load conditions with reduction of the membrane thickness from 50 to 15 μm, however further decrease in membrane thickness from 15 to 10 μm leads to reduction in cell voltage at high current loads. A thick anode CL is found to be beneficial under wet operating conditions assuming more pore space is provided to accommodate liquid water, whereas under dry operating conditions, an intermediate thickness of the anode CL is beneficial. When studying the impact of catalyst layer thickness, too thin a catalyst layer again shows reduced performance due to increased ohmic resistance ruled out the performance of the MEAs which have identical Pt crystallite sizes on the cathode CLs i. e. the thinnest the cathode CL, the highest the voltage were achieved at a defined current load. Adaptation of the operating conditions is highly anticipated to achieve the highest MEA performance.
In this work, we investigated the influence of catalyst supports, particularly Brunauer, Emmett, and Teller (BET) surface area of the catalyst support materials, on membrane electrode assembly (MEA) performance. Keeping the anode catalyst layer (CL), membrane, Pt loading, and operating condition unchanged, we prepared cathode CLs using catalysts of identical Pt content (30 wt% Pt) which were supported on carbon black materials having different BET surface areas. We observed optimum cell voltage at high current load when using cathode catalyst layers prepared from catalysts supported on carbons having medium-BET surface area. High-BET surface area supports, although beneficial at low current density as well as low-BET surface area supports, led to increased voltage losses at high current load due to mass transport limitations which can be explained by the electrochemically active surface area available and water management in the catalyst layer.
Adsorption separation of phenol from aqueous solution using activated carbon was investigated in this work. The adsorbent was prepared from coconut shell and activated by physical activation method. The coconut shell was first carbonized at 800°C under nitrogen atmosphere and activated by CO 2 at the same temperature for one hour. The prepared activated carbon was characterized by Scanning Electron Microscope (SEM) and BET Surface Analyzer and by the determination of iodine number as well as Boehm titration. The iodine number indicates the degree of relative activation of the adsorbent. The equilibrium adsorption isotherm phenol from aqueous solution was performed using liquid phase batch adsorption experiments. The effect of experimental parameters including solution pH, agitation time, particle size, temperature and initial concentration was investigated. The equilibrium data was analyzed using Langmuir and Freundlich adsorption model to describe the adsorption isotherm and estimate the adsorption isotherm parameters. The results indicate the potential use of the adsorbent for removal of phenol from the aqueous solution.
Polymer electrolyte membrane fuel cells (PEMFC) are promising candidates for the replacement of internal combustion engines. Still, alongside the necessary enhancement of the mass activity of cathode catalyst material, the performances of the PEMFC cathode must be improved in the high current densities range where the O2 reactant mass transport towards the catalytic site is limiting for the reaction rate [1]. High current density performance of the PEMFC strongly depends on the ionomer distribution in the catalytic layer constituting the electrode, which depends on the solvent used for the catalyst ink preparation [2]. From different studies, it has been observed that the nature of the solvent composition modifies the resulting structure and size of the dispersed ionomer agglomerates in the catalyst ink [3–5]. The main objective of our investigation is to resolve in more detail the influence of the ink solvent composition on the PEMFC performances. For this purpose, the agglomerate size distribution of the 1100 EW Nafion® ionomer dispersed into various solvents was determined at first by dynamic light scattering (DLS) in a systematic fashion and found to be strongly influenced by the kind of alcohol (isopropanol, ethanol and methanol) and its concentration in water. Then, in order to attempt a correlation between the agglomerate size of the ionomer and the MEA performances, cathode catalyst layers were prepared from inks with these alcohols at different concentrations, while keeping all the other parameters in the CCM preparation unchanged. Electrochemical impedance spectroscopy (EIS) and O2 mass transport resistance measurements (O2-MRT) were performed in addition to the recording of single cell polarization curves. The latter were modeled following the equation suggested by Larminie et al. [6] to discriminate the kinetic, ohmic and mass transport overvoltages (losses). The ink-solvent compositional characteristics significantly influence the O2 reactant mass transport overvoltages. An analog equivalent circuit including a Nernst impedance element to account for the finite O2 diffusional limitations at the cathode catalyst layer was fitted to the experimental EIS data. The Warburg parameter scales very well with the O2 transport resistance through the catalytic layer derived from O2-MRT measurements, this strengthening the robustness of the overall set of experimental data. As the fraction of ionomer agglomerates in the range 50-500nm progressively increases in the catalyst ink up to ca. 37-45%, the losses attributed to the limited O2 mass transport to the catalytic sites are lowered by down to ca. 70% at 1.76 A∙cm-2 current load under the given cell testing conditions, independently of the nature of the alcohol and its relative content. For the higher fraction of ionomer agglomerates in this size range, no further change is observed in the O2 transport loss parameter. These results highlight quantitatively the significant influence of the size distribution of ionomer agglomerates on the cell performances under high current loads and suggest a convolution with other parameters, such as, e.g., the porous structure of the catalyst layer, that has yet to be quantitatively asserted. References [1] A. Kongkanand, M.F. Mathias, J Phys. Chem. Lett. 7 (2016) 1127–1137. [2] A. Orfanidi, P.J. Rheinländer, N. Schulte, H.A. Gasteiger, J. Electrochem. Soc. 165 (2018) F1254-F1263. [3] T.T. Ngo, T.L. Yu, H.-L. Lin, Journal of Power Sources 225 (2013) 293–303. [4] S.A. Berlinger, B.D. McCloskey, A.Z. Weber, J. Phys. Chem. B 122 (2018) 7790–7796. [5] M. Yamaguchi, T. Matsunaga, K. Amemiya, A. Ohira, N. Hasegawa, K. Shinohara, M. Ando, T. Yoshida, J. Phys. Chem. B (2014) 141210091239007. [6] J. Larminie, A. Dicks, Fuel Cell Systems Explained, Second Edition.
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