Oxygen reduction kinetics

Alkaline Fuel Cell. The electrolyte ia the alkaline fuel cell is concentrated (85 wt %) KOH ia fuel cells that operate at high (- 250° C) temperature, or less concentrated (35—50 wt %) KOH for lower (<120° C) temperature operation. The electrolyte is retained ia a matrix of asbestos (qv) or other metal oxide, and a wide range of electrocatalysts can be used, eg, Ni, Ag, metal oxides, spiaels, and noble metals. Oxygen reduction kinetics are more rapid ia alkaline electrolytes than ia acid electrolytes, and the use of non-noble metal electrocatalysts ia AFCs is feasible. However, a significant disadvantage of AFCs is that alkaline electrolytes, ie, NaOH, KOH, do not reject CO2. Consequentiy, as of this writing, AFCs are restricted to specialized apphcations where C02-free H2 and O2 are utilized. 

Zhang J, Vukmirovic MB, Sasaki K, Nilekar AU, Mavrikakis M, Adzic RR. 2005a. Mixed-metal Pt monolayer electrocatalysts for enhanced oxygen reduction kinetics. J Am Chem Soc 127 12480-12481. 

Murthi VS, Urian RC, Mukeijee S. 2004. Oxygen reduction kinetics in low and medium temperature acid environment Correlation of water activation and surface properties in supported Pt and Pt alloy electrocatalysts. J Phys Chem B 108 11011-11023. 

Hsueh KL, Gonzalez ER, Srinivasan S. 1983. Electrolyte effects on oxygen reduction kinetics at platinum—A rotating-ring disk electrode analysis. Electrochim Acta 28 691-697. 

Komanicky V, Menzel A, You H. 2005. Investigation of oxygen reduction kinetics at (111)-(100) nanofaceted platinum surfaces in acidic media. J Phys Chem B 109 23550-23557. 

The AFC has the highest electrical efficiency of all fuel cells but it only works properly with very pure gases, which is considered a major drawback in most applications. The KOH electrolyte, which is used in AFCs (usually in concentrations of 30-45 wt%), has an advantage over acidic fuel cells, i.e., the oxygen reduction kinetics is much faster than in acid medium. 

Alkaline fuel cells (AFC) — The first practical -+fuel cell (FC) was introduced by -> Bacon [i]. This was an alkaline fuel cell using a nickel anode, a nickel oxide cathode, and an alkaline aqueous electrolyte solution. The alkaline fuel cell (AFC) is classified among the low-temperature FCs. As such, it is advantageous over the protonic fuel cells, namely the -> polymer-electrolyte-membrane fuel cells (PEM) and the - phosphoric acid fuel cells, which require a large amount of platinum, making them too expensive. The fast oxygen reduction kinetics and the non-platinum cathode catalyst make the alkaline cell attractive. 

Adzic, R.R. and Wang, J.X., Structures of surface adlayers and oxygen reduction kinetics, Solid State Ionics, 150, 105, 2002. 

Figures 2-4 show a comparison of the ring-disk electrode for the oxygen reduction kinetic data along with the base voltammetry in oxygen-free solutions for each Vi hkl) surface. Clearly, the kinetics of the ORR on VtQikl) surfaces vary with crystal face in a different manner depending on the solution. In perchloric acid solution. Figure 2, the variation in activity at 0.8-0.9 V is relatively small between the three low-index faces, with the activity increasing in the order (100) < (110) (lll). A similar structural sensitivity is observed in KOH, Figure 3, with the activity...

The high temperature improves the oxygen reduction kinetics dramatically eliminating the need for precious metal catalysts. The molten carbonate (usually a Li-K or Li-Na carbonate) is stabilized in a matrix (LiA102) that can be supported with AI2O3 fibers for mechanical strength. 

Fig. El 5.1 Oxygen reduction kinetics during cathodic protection in sea water.

Platinum alloy catalysts have been found to improve the oxygen reduction kinetics. Shrinking of the Pt-Pt distance as well as electronic effects have been used to explain this phenomenon. Alloying of platinum with non noble metals such as cobalt, nickel or iron after extended contact with acid electrolytes left platinum rich skins on the surface, still providing improved kinetics. Pathways of the nrai... 

Gottesfeld S, Raistrick ID, Srinivasan S. Oxygen reduction kinetics on a platinum RDE coated with a recast Nafion film. J Electrochem Soc 1987 134(6) 1455-62. 

Qiao J, Xu L, Ding L, Shi P, Zhang L, Bake R, et al. Effect of KOH concentration on the oxygen reduction kinetics catalyzed by heat-treated Co-Pyridine/C electrocatalysts. Int J Electrochem Sci 2013 8 1189-208. 

The reduction of O2 is thermodynamically favorable, but the reaction kinetics are relatively slow. Using an electrode material with a high surface area, such as activated carbon powder, can overcome the slow oxygen reduction kinetics by presenting a large number of sites at which O2 can be reduced. A small amount of a conductive carbon material may also be added to increase the electrical conductivity of the cathode. 

Mitterdorfer, A., and Gauckler, L. J. (1998). LazZrzO formation and oxygen reduction kinetics of the Lao.ssSro uMnyOs, 02(g) vertical bar YSZ system. Solid State Ionics 111 183-218. 

Renslow R, Donovan C, Shim M, Babauta J, Nannapaneni S, Schenk J, Beyenal H. Oxygen reduction kinetics on graphite cathodes in sediment microbial fuel cells. Phys Chem ChemPhys 2011 13 21573-21584. 

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