Optimizing the synthesis of carbon nanofiber based electrocatalysts for fuel cells

Abstract

This work deals with an optimization of the platinum dispersion on low surface area carbon nanofibers (CNFs) by using different synthesis procedures and its electrocatalytic activity toward oxygen reduction. The selected CNFs were characterized by a BET surface area of ca. 100 m2g−1 and were in-house synthesized by the decomposition of CH4 at 700°C. Pt nanoparticles were deposited by using four different synthesis routes. A metal concentration of 20wt% was confirmed by EDX and TGA. Two classical impregnation routes were employed, one using NaBH4 as reducing agent at 15°C and the second one using formic acid at 80°C. Two alternative processes consisted in a microemulsion procedure followed by reduction with NaBH4 and a colloidal route by using the sulphite complex method followed by reduction with hydrogen. The main differences regarded the platinum crystal size varying from 2.5nm for the colloidal route to 8.1nm for the impregnation route (formic acid). The classical impregnation procedures did not result appropriate to obtain a small particle size in the presence of this support, whereas microemulsion and colloidal methods fit the requirements for the cathodic oxygen reduction reaction in polymer electrolyte fuel cells, despite the low surface area of CNFs. The catalysts were subjected to an accelerated degradation test by continuous potential cycling. Although the initial activity was the highest for the microemulsion based catalyst, after the accelerated degradation test the colloidal based catalyst experienced a relatively lower loss of performance.