Abstract
Electrocatalysts for PEFC are generally composed by Pt dispersed on carbon supports and have an important role to determine the performance of PEFC. Decrease in Pt active sites during the long-time use becomes a serious problem for practical use of PEFC. Pt particles have tendency to agglomerate, or dissolve and re-precipitate under the potential cycles, resulting in the growth of particles. In this study, suppressing such Pt particle growth has been focused on. So far, increasing the durability of electrocatalysts by encapsulating Pt into the nanochannnels of mesoporous carbon (MC) has been reported in our group.1 The basic idea comes from reducing Pt mobility on the curved carbon surface, which has also been supported by theoretical study.2 In this particular report, the effect of pore characteristics, such as pore diameter and pore volume, on PEFC performance are evaluated. MCs were made from the self-organization formaldehyde/resorcinol and Pluronic F127,3 but the procedure was slightly modified for each kind of MCs. Then, electrocatalysts were synthesized from platinum(II) acetylacetonate as a precursor by depositing ca. 30 wt% Pt on MCs. These MC based materials were used for the cathode, and a standard Pt/Ketjen black catalyst (TEC10E50E, TKK Corp.) was used for the anode, in order to prepare membrane electrode assemblies (MEAs). Current-voltage (IV) characteristics of MEAs were measured in this study. Then, ohmic loss, concentration loss, and overvoltage were further analyzed separately after ohmic resistance was found by impedance measurements. When three electrocatalyts, a standard Pt/MC, Pt/air-treated MC, and Pt/high pore volume-MC, are compared, the concentration overvoltage resulted in high with the order of a standard Pt/MC > Pt/high pore volume-MC > Pt/air-treated MC. Regarding to the activation overvoltage, it is reduced with the order of Pt/air-treated MC < a standard Pt/MC < Pt/high pore volume-MC. The correlation between the pore structure and the PEFC performance will be discussed.
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