Effect of Cathode Catalyst Layer Structure on the Performance of PEFC

Abstract

One of the routes to promote PEFC commercialization is to reduce its manufacture cost. Platinum represents more than 50% of PEFC cost. Therefore, two targets can be considered; reduction of platinum loading (g/cm2) at cathode, and increase specific catalytic activity towards reaction (mA/cm2 pt). On the other hand, the effectiveness factor has an inherent relation with current density and mass transfer of reactants (oxygen and proton), which are existing simultaneously. For investigating cathode behavior, two dimensionless moduli, representing diffusion limitations due to oxygen and proton mass transfer resistances, have been proposed 1. To estimate mass transport resistances, effectiveness factor and intrinsic reaction rate constant, experiments were carried out by varying cathode catalyst layer (CCL) structure on a membrane electrode assembly (MEA). The MEA, fabricated by decal transfer method, consisted of a Nafion membrane (NR-212, 50 μm) with Pt/C weight ratio of 0.3, 0.4 and 0.5 in 10 μm CCL. The ionomer (I)/C ratio was 1. The CCL was prepared by two methods. The first, Pt particles were supported on carbon (Ketjen black) relevant to the required Pt/C ratio (Standard catalyst preparation). The second, lower Pt/C ratios were manipulated by adding carbon black (CB) to a prepared catalyst mixture contained 50% Pt/C where Pt loading was 0.3 mg/cm2 (CB dilution method). The IR corrected voltage (electromotive force) was calculated by measuring the polarization curves and membrane resistance using an electrochemical measurement system. The impedance spectra were measured in a range of frequency from 10 mHz to 100 kHz. The analysis of the results using our dimensionless moduli approach may support having deeper insight that could accelerate the development of PEFC. Reference: M. Kawase et al., AIChE J., 63, 249–256 (2017) http://doi.wiley.com/10.1002/aic.15545. Figure 1