Effect of surface groups on the electrocatalytic behaviour of Pt-Fe-Co alloy-dispersed carbon electrodes in the phosphoric acid fuel cell

Effect of surface group on the electrocatalytic behaviour of 10 wt.% Pt-Fe- Co alloy-dispersed carbon (Pt-Fe-Co/C) electrode has been investigated as f unctions of applied potential and duration in 85% H3PO4 solution of 145 deg rees C, using Fourier transform infrared (FTIR) spectroscopy, combined with nc-impedance spectroscopy, potentiostatic current transient technique, and potentiodynamic polarization experiment. It was shown from FTIR spectra th at surface group formed in this work: mainly comprises carboxyl group and t hat the formation potential of carboxyl group lies between 600 and 700 mV(R HE). From increase of charge transfer resistance (R-ct), and decrease of el ectrocatalytic activity for oxygen reduction with immersion time, it is sug gested that above the formation potential of carboxyl group, further format ion of carboxyl group on the carbon support around the catalyst particle re duces active surface area of the catalyst particle with immersion time. On the other hand, below the formation potential, dissolution of carboxyl grou p previously formed on the carbon support raises active surface area of the catalyst particle. Ln the present study, relationship between electrocatal ytic aspect of the electrode, and the amount of carboxyl group formed on th e carbon support around the catalyst particle was well discussed with a sch ematic illustration. The illustrative representation is underlain by format ion on and dissolution from the catalyst particle of carboxyl group which c ause the rise and fall in circumferential coverage of carboxyl group, respe ctively and hence thr reduction and elevation in active surface area of the catalyst particle. (C) 1999 Elsevier Science S.A. All rights reserved.