Enhanced Stability of PtCo catalysts for PEMFC

Abstract

In this work it is shown that PtCo/C catalysts give a 2× mass activity enhancement in oxygen reduction activity, compared to Pt/C. Through the use of Pt and PtCo catalysts of varying surface area, clear evidence of a particle size effect on oxygen reduction activity was found. Investigation of the effects of cathode potential cycling in both wet electrolyte cells (1M H 2 SO 4 ) and as small MEAs revealed high metal surface area stability and stable oxygen performance over 10,000 cycles for the PtCo/C alloys compared to Pt/C. TEM analysis of MEA cross-sections after cycling show clear evidence of Pt migration towards and into the PEMFC membrane for Pt/C cathodes, whilst PtCo/C materials show minimal deterioration. The larger crystallite sizes present in PtCo particles therefore confer higher stability to cycling and resistance to dissolution, whilst use of an alloy produces high mass activity, despite a lower metal surface area compared to Pt/C.

Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

“…Other investigators have made observations very similar to those of Strasser and co-workers regarding the performance of Pt-alloys/C in comparison to Pt/C over long time scales or under potential cycling in a PEMFC, 37,152,[154][155][156][157] namely that: (a) similar to Pt, the mass activity of Pt-alloys decreases slightly (b) whereas the specific activity of Pt is stable or tends to increase the specific activity of Pt-alloys changes little or sometimes decreases and (c) there is a slight decrease in the electrochemically active surface area upon the alloys, in contrast to the pronounced decrease exhibited by Pt. The improved retainment of the surface area of Pt-alloys/C over Pt/C in a PEMFC may suggest that the presence of the less noble solute metal actually stabilises the catalyst.…”

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…68 To examine the effects of atomic ratios (i.e., Pt to base metals), the fuel cell activity and stability of PtM/C (M = Co, Cr, Fe, Ni and Mn) have been studied; it was found that PtM alloys with a 3 : 1 Pt : M ratio exhibited much higher activity and better stability. 69,70 For example, comparison stability tests on a single fuel cell with Pt/C and Pt 3 Co/C as cathode catalysts showed that the latter had greater stability. The degradation rate for Pt/C was 0.98 mV h À1 , twice that of Pt 3 Co/C (0.44 mV h À1 ).…”

The Effect of Dynamic and Steady State Voltage Excursions on the Stability of Carbon Supported Pt and PtCo Catalysts

“…Application of accelerated durability tests by Popov et al (14) to 20%Pt/C and a 20%Pt 3 Co/C alloy showed enhanced catalyst particle stability from addition of an alloying element but loss of Co during the first 100hrs of testing adversely affected membrane electrode assembly (MEA) performance. Previous work by the authors demonstrated PtCo alloy catalysts on high surface area carbon supports retained surface area and activity over 10,000 voltage cycles from 0.6-1V (6).…”

“…This Ostwald ripening process results in coarsening of catalyst particles reducing overall active area and the presence of dissolved Pt in the electrolyte in both wet cell and MEA tests (5,6,7) as a result of potential cycling.…”