Influence of Experimental Conditions on the Catalyst Degradation in the Durability Test

Abstract

Accelerated durability tests (ADTs) were carried out for a carbon-supported platinum catalyst using a rotating disk electrode at various rotation rates for various catalyst loadings. The electrochemical surface area (ECSA) of platinum, TEM-observed relative particle size distribution, and Pt ion concentration in the electrolyte were analyzed. Their results were combined to provide the absolute change in the particle size distribution. The loss of the normalized ECSA increased with increasing the rotation rate and/or decreasing the catalyst loading. The detailed analysis showed that the reciprocal of the normalized ECSA loss rate linearly increased with the increases in ω −1/2 (ω: angular frequency of rotation) and the catalyst loading; these results suggests that ECSA loss in ADTs is significantly affected by Pt ion diffusion in the electrolyte. By extrapolating these linear relations to zero, the ECSA loss rate at the hypothetical conditions, in which all the dissolved platinum ions would flow out to the electrolyte without re-deposition, was obtained.

Importance of non-intrinsic platinum dissolution in Pt/C composite fuel cell catalysts

“…[30][31][32] Platinum dissolution has been extensively studied before -either in the form of a polycrystalline disk [33][34][35][36] or as a nanoparticulate catalyst. [3][4][5][6]29,[37][38][39][40] It has been shown that the electrochemical dissolution of Pt is predominantly a transient phenomenon occurring due to the interplay of Pt oxidation and reduction processes. These processes can be manipulated by changing the electrochemical treatment (scan rate, anodic and cathodic potential window), gas atmosphere, electrolyte, impurities, thickness of the catalyst layer, 3,33,36,37,[41][42][43][44] and Pt nanoparticle size as well as by the addition of alloying metals.…”

“…3,48,49 Specifically, under a slow potentiodynamic regime and using the same type of carbon support, dissolution was observed to be faster the smaller the Pt nanoparticles were (see ESI, † S2.1). The effect of catalyst layer thickness on Pt dissolution, however, has only recently been proven in a conventional rotating disc electrode (RDE) study 40 by using a highly sensitive coupled analytical technique, namely SFC-ICP-MS. 39 Quite surprisingly, using these highly sensitive methods and systematically varying the catalyst loading of the electrodes showed that the Pt dissolution rate decreased as the loading increased. This was attributed to (i) an increased probability of Pt ions being trapped inside rather than diffusing out of the porous catalyst layer when the loading was higher.…”

Fabrication and Cell Analysis of a Pt/SiO2Platinum Thin Film Electrode

“…10-12 However, the chemical and electrochemical stabilities of the carbon supports, 13,14 as well as the dissolution of platinum particles, [15][16][17] raise concern about the durability of the catalyst. Furthermore, the oxygen reduction reaction (ORR) activity per surface area of platinum (the specific activity) decreases with reducing the particle size.…”

“…Great efforts have been made in improving performance of those particulate catalysts by reducing particle size, 3 alloying, [4][5][6][7][8][9] or applying core-shell structure. [10][11][12] However, the chemical and electrochemical stabilities of the carbon supports, 13,14 as well as the dissolution of platinum particles, [15][16][17] raise concern about the durability of the catalyst. Furthermore, the oxygen reduction reaction (ORR) activity per surface area of platinum (the specific activity) decreases with reducing the particle size.…”

“…Furthermore, the oxygen reduction reaction (ORR) activity per surface area of platinum (the specific activity) decreases with reducing the particle size. 3,[17][18][19][20][21][22] These problems limit further improvement of the dispersed catalysts.…”