Influence of phosphate anion adsorption on the kinetics of oxygen electroreduction on low index Pt(hkl) single crystals

Abstract

The detrimental effects of phosphate anion adsorption on the oxygen reduction reactions (ORR) on low index Pt single crystal electrodes were studied in 0.1 M perchloric acid by using a hanging meniscus rotating disk electrode in the presence of varied concentrations of H(3)PO(4). The kinetic current for ORR decreased dramatically on Pt(100), Pt(110), Pt(111), and PtSn(111) even with the addition of a small amount (1 mM) of H(3)PO(4) into the perchloric acid solution, most probably due to the adsorption of phosphate anions onto the Pt active sites that impeded the electroreduction of O(2). Remarkably, the extent of decline was found to vary with the specific single crystal surface, following the order of Pt(111) > PtSn(111) > Pt(110) ∼ Pt(100). Consistent behaviors were also observed in Tafel analysis and in electrochemical impedance spectroscopic measurements. Within the present experimental context, Pt(110) was found to be the optimal crystal surface for ORR in phosphoric acid fuel cells with the smallest charge transfer resistance, whereas the poisoning effects of phosphate anion adsorption were the most pronounced on Pt(111), most likely because the phosphate anions primarily adsorbed on the 3-fold sites on the Pt(111) faces, as manifested in in situ X-ray absorption spectroscopic measurements.

On the oxygen reduction reaction in phosphoric acid electrolyte: Evidence of significantly increased inhibition at steady state conditions

“…It is shifted to more negative potentials, especially in the H3PO4 electrolyte solution [41,42]. This observation demonstrates that the desorption/adsorption of strongly adsorbed anions influences the adsorption/desorption of hydrogen and shifts it to a lower potential [43]. As mentioned above, the onset potential for the formation of oxygenated species starts earlier (lower potential) in HClO4 than in the other two acids.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] for an overview. Most studies are related to surface science and therefore target the structure sensitivity of anion adsorption on well-defined single crystal surfaces.…”

2-Sulfoethylammonium Trifluoromethanesulfonate as an Ionic Liquid for High Temperature PEM Fuel Cells

“…To get a first insight, C D was calculated from the charging current density, j d , in the double layer region (U ≈0.5 V) according to the following equation: [13] For both electrolytes, C D tends to increase with temperature (see Fig. 8).…”

“…The adsorption of phosphate by platinum has been studied for more than 30 years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] by means of cyclic voltammetry (CV), [2][3][4][5]9,[11][12][13][14][16][17][18][19][20][21] rotating disc electrode measurements (RDE), [2][3][4][5]8,9,11,13,14 electrochemical impedance spectroscopy (EIS), 13,16,22 transient measurements, 9,23,24 Fourier transform infrared spectroscopy (FTIR), 20,[25][26][27] electrochemical quartz crystal microbalance (QCM), 18 radio tracer experiments...…”

“…(ii) The low solubility of oxygen in phosphoric acid. (iii) The slow diffusion of oxygen through the film of phosphoric acid which covers the platinum catalyst.The adsorption of phosphate by platinum has been studied for more than 30 years 1-15 by means of cyclic voltammetry (CV), [2][3][4][5]9,[11][12][13][14][16][17][18][19][20][21] rotating disc electrode measurements (RDE), [2][3][4][5]8,9,11,13,14 electrochemical impedance spectroscopy (EIS), 13,16,22 transient measurements, 9,23,24 Fourier transform infrared spectroscopy (FTIR), 20,25-27 electrochemical quartz crystal microbalance (QCM), 18 radio tracer experiments, 28 X-ray photoelectron spectroscopy (XPS) 17 and X-ray absorption spectroscopy (XAS). 14,15 The in-operando XAS measurements recently published by Kaserer et al show the adsorption behavior of H 3 PO 4 species on Pt/C fuel cell cathode catalysts in the temperature range of 50-170…”