Editors' Choice—Electrochemically Active Surface Area Measurement of Aged Pt Alloy Catalysts in PEM Fuel Cells by CO Stripping

Abstract

The use of hydrogen adsorption/desorption (HAD) is a convenient method to measure the Pt surface area of a catalyst. However, it was shown that electrochemical charges measured by this technique can underestimate the Pt surface area by up to a factor of two for small Pt nanoparticles or Pt alloy nanoparticles. Electrooxidation of CO, so-called CO stripping, has been shown to be more accurate. Yet measurements of CO stripping in MEAs are scarce, especially on high activity alloy catalysts. In this study we investigated CO stripping and the ratio between Pt surface areas measured by CO and by HAD on several Pt and Pt alloy catalysts. The effects on these measurements of temperature and catalyst aging by voltage cycling are discussed.

Enhanced oxygen reduction activity of platinum subnanocluster catalysts through charge redistribution

“…On the other hand, ECSA determined from hydrogen adsorption/desorption is smaller than the larger NP of Pt/C. This probably originates from site specific adsorption 44 of hydrogen on the smaller NCs, which also supports the idea of a large change in the surface chemical nature for Pt 6 catalysts; Pt sites charged neutral presumably act as adsorption sites for hydrogen. The nature of site-specificity for sub-NCs, originating from a greater flexibility of charge redistribution, will enable much higher activity by further alloying and strong support interactions through electronic interaction (ligand and strain effects) 16 in addition to the geometric ensemble effect.…”

“…The d-orbital-center energy is much higher than the d-band center for larger NPs and the bulk (111) surface. 44 Based on our knowledge of the correlation between the d-band-center and ORR activity, 41 the enhanced MA for Pt 6 /GC can be attributed to its electronic structure changed by a large degree of charge separation in the tiny NCs. On the other hand, ECSA determined from hydrogen adsorption/desorption is smaller than the larger NP of Pt/C.…”

Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation: A Voltage Loss Analysis

“…This superposition is especially dominant at low rf, as the rate of the HER above 0 V RHE in cyclic voltammetry is mostly thermodynamically controlled (i.e., it does not depend significantly on the active Pt surface area), whereas the pseudo-capacitive H UPD charge scales directly with the available Pt surface area. Hence, the strong decrease of the rf in the course of the voltage cycling AST renders the determination of the ECSA via the H UPD method increasingly erroneous, requiring the implementation of CO stripping to reliably determine the remaining Pt surface area for very low rf values, 43 i.e., towards the end of the aging protocol. Representative CO stripping measurements are shown in Figure 4b after subtraction of the second anodic scan.…”

Understanding the Role of Ir during Methanol Oxidation at PtxIryAlloy Nanoparticles

“…Based on the literature, the electrochemical surface area (ECSA), obtained from CO stripping, is likely to be more accurate than the surface areas obtained from Hupd measurements, 51,52 as CO can replace the PVP carbonyl group more easily than H atoms can. However, the oxidation of CO gas that may be trapped within the residual capping agent surface layer may also occur, thus potentially resulting in an over-estimation of the ECSA.…”