Oxygen reduction reaction catalyst stability

Bezerra C, Zhang L, Liu H, Lee K, Marques A, Marques E, Wang H, Zhang J, (2007). A review of heat-treatment effects on activity and stability of PEM fuel cell catalysts for oxygen reduction reaction Journal of Power Sources 173 891-908 Blesl M, Fahl U, Ohl M, (2004). HochtemperaturbrennstofFzellen und deren Kostenentwicklung. BWK, 56 72-56... 

Bezerra CWB, et al. A review of heat-treatment effects on activity and stability of PEM fuel cell catalysts for oxygen reduction reaction.) Power Sources 2007 173(2) 89f-908. 

Liu G, Li XG, Ganesan P, Popov BN (2010) Studies of oxygen reduction reaction active sites and stability of nitrogen-moditied carbon composite catalysts for PEM fuel cells. Electrochim Acta 55(8) 2853-2858... 

Liu G, Li X, Popov BN (2009) Stability study of nitrogen-modified carbon cmnposite catalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells. ECS Trans 25 1251-1259... 

Abstract In this chapter, we review recent works of dealloyed Pt core-shell catalysts, which are synthesized by selective removal of transition metals from a transition-metal-rich Pt alloys (e.g., PtMs). The resulted dealloyed Pt catalysts represent very active materials for the oxygen reduction reaction (ORR) catalysis in terms of noble-metal-mass-normalized activity as well as their intrinsic area-specific activity. The mechanistic origin of the catalytic activity enhancement and the stability of dealloyed Pt catalysts are also discussed. 

Ma X, Meng H, Cai M, Shen PK (2012) Bimetallic carbide nanocomposite enhanced Pt catalyst with high activity and stability for the oxygen reduction reaction. J Am Chem Soc 134(4) 1954-1957... 

Electrocatalytic Reduction of Oxygen. Oxygen reduction reaction (ORR) occurs on the cathode side of low temperature fuel cells and heavily loaded Pt/C is the most common electrocatalyst. Replacement of ORR catalysts with less expensive materials would have higher technical impact than for anode catalysts. Transition metals loaded carbides and carbide-metal codeposited carbon have been investigated for ORR application. For example, 40 wt% Pt/WC electrocatalyst prepared with RDE electrode showed a cathodic current (-5 x 10 A) similar to that of 40 wt% Pt/C with 0.5 M H2SO4, 100 mv/s and 2000 rpm (160). Also, 40 wt% Pt/WC exhibited electrochemical stability after 100 cycles of cyclic voltammetry from 0 to 1.4 V (vs RHE), whereas the cathodic current of 40 wt% Pt/C disappeared after 100 cycles. 

Transition metal carbide, in particular tungsten carbide, is another type of nonnoble catalyst showing activity towards the oxygen reduction reaction. However, the main catalytic activity of carbide is not in the oxygen reduction reaction, but rather in other reactions such as H2 oxidation. Mazza et al. [73] reported that WC, TaC, Tie, and TiN showed catalytic activity towards ORR in acid solutions. However, these materials are not stable in alkaline solution. For example, even in acid solutions, WC did not show long-term stability in the presence of O2 [73]. Lee et al. [74] found that the addition of Ta to WC could significantly improve its catalytic activity and stability. 

Obviously, the different types of interaction will lead to different kinetics and mechanisms, and different proportions of water to peroxide in the reaction product. Much has been written and speculated about these different interactions and the influence of metal d-orbital characteristics on the overall ORR. Reviews covering this aspect of the subject can be found in references such as [103] and [105]. On the whole, these conclusion can be drawn from the significant body of research on this topic (a) Fe and Co macrocyclic complexes appear to constitute the best catalysts for oxygen reduction (b) Ir complexes also appear to be quite active (c) the redox potential for the metal ion couple plays a major role in dictating the activity of the ORR, with optimal redox potentials existing for maximum activity (d) many of the non-noble metal catalysts lack the long-term stability needed for practical fuel cell applications and (e) heat treatment of supported non-noble metal catalysts tends to increase both their activity towards oxygen reduction and their stability, but optimum heat treatments achieve the best balance of the two. 

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