A STUDY ON THE FORMATION OF SURFACE FUNCTIONAL-GROUPS DURING OXYGEN REDUCTION ON A PLATINUM-DISPERSED CARBON ELECTRODE IN AN 85-PERCENT H3PO4 SOLUTION AT ELEVATED-TEMPERATURE

The formation of the surface functional group during oxygen reduction on a platinum-dispersed carbon (Pt/C) electrode has been investigated in an 85% H3PO4 solution at 145 degrees C with concurrent blowings of a mixture of oxygen and nitrogen by using Fourier transform infrared ( FTIR) spectroscopy supplemented by AC-impedance spectroscopy. AC-imped ance spectra indicated that the reactivity of H2O2 towards the chemica l and electrochemical decomposition increases with increasing oxygen p artial pressure. From the results of FTIR spectroscopy, the surface fu nctional group formed during oxygen reduction proved to be composed ma inly of quinone and carboxyl groups. By comparison of the FTIR spectra obtained from the pure and Pt/C powders treated in a H2O2-containing aqueous solution with those from the Pt/C powder treated in H3PO4 solu tion, it is concluded that the carboxyl group formation dominates over the quinone group generation in the low oxygen partial pressure range ; however, it is quite the opposite in the high oxygen partial pressur e range. (C) 1998 Elsevier Science Ltd. All rights reserved.