ORR Catalyzed by Transition Metal Chalcogenides

Chalcogenides can catalyze either 2-electron or 4-electron O2 reduction, depending on the catalysts used. For example, Mo4Ru2Ses, Rui.92Moo.o8Se04, RuxSy(CO)n, RUxSey, etc. catalyze 4-electron transfer [62-68], while W-Co-Se catalyzes a 2-electron O2 reduction reaction [69]. 

M04 2RU1 gSeg cluster and the redox couple (O2/H2O) at the interface, under charge transfer conditions. The insert shows a supposed interaction of the molecular bridge type at two adjacent transition metal atoms [63], (Reprinted with permission from J Am Chem Soc 1987 109 3251-7. Copyright 1987 American Chemical Society.) 

The catalytic activity of a chalcogenide towards ORR can reach a level of 30—40% of the Pt catalyst activity. The Tafel slope varies from 100 mV/dec up to 167 mV/dec, depending on the materials used and the preparation method. Duron et al. [66] reported two Tafel slopes for ORR on a RuxSy(CO)n cluster 124 mV/dec at low overpotential and 254 mV/dec at high overpotential. Susac et al. [72] reported a Tafel slope of 167 mV/dec on Co-Se catalyst. There seems to be no reported data in the literature about the exchange current density of ORR catalyzed by chalcogenides. 

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