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

Abstract

To improve the stability of Pt-based catalysts to meet the targets set for automotive fuel cell operation, a detailed understanding of the mechanisms of corrosion and Pt particle stability is required. The stability of Pt and PtCo on both high-area and low-area carbon supports has been studied using both dynamic and steady state voltage excursion measurements. At 1.2V steady state, the catalysation of carbon did not significantly increase the rate of carbon corrosion. However, corrosion rates of the low area carbon was 1/20 th that of the high-area carbon. Under dynamic cycling, the stability of small Pt particles was found to be poor due to dissolution/sintering on the high-area carbon, however the PtCo alloy particles were found to be very stable on both the high-area and low-area carbons. In addition, it has been found that Pt oxide/reduction can catalyse carbon corrosion with both high and low-area carbons.

Carbon Corrosion in PEM Fuel Cells and the Development of Accelerated Stress Tests

“…A large number of PEMFC studies combined external potential control with cell exhaust analysis to directly measure complete carbon oxidation (CO 2 production) under a range of operating conditions. [14][15][16][17][18][19] Representative of this body of literature are the works by Shen et al, 20 who used a reference electrode to measure the interfacial potentials, and Brightman and Hinds, 21 who developed an innovative reference electrode array to characterize the transient profiles of cathode potentials. Kreitmeier et al 22 constructed a cell with linear parallel channels and multiple gas extraction ports in the cathode flow field to characterize carbon corrosion by measuring the local CO 2 concentrations using a mass spectrometer.…”

Fuel Cell Perfluorinated Sulfonic Acid Membrane Degradation Correlating Accelerated Stress Testing and Lifetime

“…After potential cycling with Pt/C cathodes, TEM analysis of MEA cross sections reveal Pt migration toward and into the PEM, while PtCo/C materials show negligible degradation. 172 Because the PtCo/C crystallites were larger than those of Pt/C, the alloy had higher resistance to dissolution. Improved membrane stability was observed for a cell containing PtCo/C compared with a cell containing Pt/C and was attributed to formation of a Pt band in the cell containing Pt/C.…”

“…After cycling the potential from 0.87 to 1.2 V vs RHE, Yu et al found considerable improvements in stability with PtCo compared with Pt alone. After potential cycling with Pt/C cathodes, TEM analysis of MEA cross sections reveal Pt migration toward and into the PEM, while PtCo/C materials show negligible degradation . Because the PtCo/C crystallites were larger than those of Pt/C, the alloy had higher resistance to dissolution.…”

Impact of Cold Start and Hot Stop on the Performance and Durability of a Proton Exchange Membrane (PEM) Fuel Cell

“…The extent of the COR was found to be timedependent with a peak corrosion current occurring immediate after the start/stop. 12,13 In this time period, it is also possible that the rates of the WOR and COR are affected by charge/discharge of the electrode double layers on the Pt (for the WOR) and carbon (for the COR) surfaces. 12 In Figure 9, the sudden jump after 15:07-hour mark was indicative of a limited water supply for the WOR (mass transport limit) but, due to the extremely low CD, it still had not reached the COR onset potential.…”

“…12,13 In this time period, it is also possible that the rates of the WOR and COR are affected by charge/discharge of the electrode double layers on the Pt (for the WOR) and carbon (for the COR) surfaces. 12 In Figure 9, the sudden jump after 15:07-hour mark was indicative of a limited water supply for the WOR (mass transport limit) but, due to the extremely low CD, it still had not reached the COR onset potential. CV data confirmed that there was no carbon corrosion on the anodic electrode after the cell was subjected to 70 mA reverse current for over 60 minutes.…”