The Effect of Metallurgical Variables on the Electrocatalytic Properties of PtCr Alloys

Abstract

In the two cases the pO 2-remains constant, but as for c~ > 0.25 the shape of the curve in Fig. 2 shows the independence of the pO ~-with Co, the first case has to be eliminated and the pO ~-is given by pO ~-= pK2 -2 log S(NaFeO2) REFERENCES l. P. Spiteri, EDF report D 554 MAT/T 40 (June 1984 11, 44 (1976).3. A. A. E1 Hosary, A. Baraka, and A. I. Abdel Rohman, ibid., 11, 163 (1976).4. Sandia National Laboratories Report 78-8256, Albuquerque, NM (Feb. 1979). 5. Sandia National Laboratories Report 80~8062, Albuquerque, NM (March 1981). 6. Sandia National Laboratories Report 81-8210, Albuquerque, NM (Feb. 1982 132, 863 (1985).12. S. L. Marchiano and A. J. Arvia, EIectrochim. Acta, 17, 861 (1972); S. L. Marchiano and A. J. Arvia, ibid., 17, 25 (1972); S. L. Marchiano, and A. J. Arvia, J. Appl. Electrochem., 4, 191 (1974). 13. A. Conte and S. Casadio, Ricerca Sci., 36, 488 (1966). 14. A. Conte and M. D. Ingram, Electrochim. Acta., 13, 1551 (1968).15. R. B. Flinn and K. H. Stern, J. Electroanal. Chem., 63, 191 (1975 37, 1893 (1975).18. G. Tridot, G. Nowogroki, J. Nicole, M. Wozniok, and J.Canone, Compt. Rend., 270 C, 204 (1970). 19. J. Th6ry, Ann. Chim., 7, 207 (1962). 20. R. Collongues and J. Th6ry, Bull. Soc. Chim. Fr, 7, 1141 (1959. D. R. Boehme and R. W. Bradshaw, High TemperatureSci., 18, 39 (1984). ABSTRACT In this investigation, the effect of alloying on catalysis, especially with respect to oxygen and the ORR, was examined. A series of PtCr alloys allowed four major aspects of alloying to be investigated: (i) effect of decreasing lattice parameter with increasing Cr content in the Pt terminal solid solution, (it) effect of an order/disorder transition, (iii) difference between intermetallic and solid solution structures, and (iv) effect of dendritic segregation. Results indicated that contrary to the findings of previous investigators, decreased lattice spacing did not correlate with an increase in ORR activity. Atomic ordering in low Cr content specimens, however, was found to generally increase catalysis. Results also indicated that disordered structures interact more strongly with impurities than the ordered structures. ORR Tafel slopes, however, were unaffected by atomic ordering although additional chromium, up to at least 35 atom percent (a/o), caused a decrease in Tafel slope apparently due to oxide reduction effects. At higher Cr concentrations, catalysis decreased due to the passive nature of chromium oxide. The change in crystal structure which occurs for the 80 a/o Cr sample and the dendritic structure, had little effect on most of the electrochemical parameters studied relative simply to the additional Cr content. The results of this work also indicated that, in general, no alloy in the PtCr system is more catalytic than pure Pt. This result is in contrast to gas diffusion cell studies which have shown significant increases in catalysis due to PtCr alloying. The Effect of Metallurgical Variables on the Electrocatalytic Properties of PtCr AlloysOxygen electrode interactions are of impo...

Effect of Reheating Treatment on Oxygen-Reduction Activity and Stability of Zirconium Oxide-Based Electrocatalysts Prepared from Oxy-Zirconium Phthalocyanine for Polymer Electrolyte Fuel Cells

“…MWCNTs (diameter = 10-15 nm, length = 3 μm, BET surface area = 260 m 2 g −1 ) were used as support and electrically conductive material. ZrOPc (0.6 g) was dissolved in N-methylpyrrolidone (80 cm 3 ) and MWCNTs (44 mg) were dispersed in the solution. The dispersion was stirred for several hours and then evaporated to deposit the ZrOPc onto the MWCNTs.…”

“…The use of platinum, however, causes high cost, and platinum resources are limited, thereby restraining the actual commercialization of PEFCs. Therefore, many researchers have improved the ORR activity and durability to reduce the usage of platinum by different methods such as alloying it with other transition metals, such as Fe, Ni, and Co, [1][2][3][4][5][6] and the formation of core-shell structures. [7][8][9][10] The drastic reduction in platium usage, however, would be difficult to achieve because the highly dispersed platinum alloys and coreshell particles generally become unstable and dissolve easily under cathode conditions, resulting in decreasing cell performance during long-term operation.…”

Oxygen Reduction Reaction on Pt and Pt Bimetallic Surfaces: A Selective Review

“…A definitive determination, however, remains elusive. Luczak et al, for example, found an increase in mass activity of a factor 1.5 to 2.5 when using PtCoCr or PtCr instead of pure Pt [9,47,48] whereas Beard et al [49] and Glass et al [50] found no change for PtCo and PtCr, respectively. Furthermore, Mukerjee et al, [51] showed that five binary Pt-M alloy electrocatalysts (M = Cr, Mn, Co, and Ni) supported on carbon produced some enhancement in the kinetics (factor of 3-5) of the ORR relative to ªstandardº supported Pt catalyst.…”

Structural, Compositional and Electrochemical Characterization of Pt–Co Oxygen‐Reduction Catalysts

“…[10] The enhanced electrocatalysis of the ORR afforded by the Pt-Co alloys has been the subject of numerous investigations. [8,11,12] Among the explanations suggested for the improved catalysis are: 1) an increase in the 5d-band vacancy in Pt; [13] 2) changes in the interatomic distance and coordination number of Pt; [14] and 3) dioxygen activation at (adjacent) Co sites. [15] But a paucity of studies that have examined the influence of the structure and composition of the alloy surface on ORR-catalysis performance remains.…”