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Abstract: To solve the problem of the catalyst-loading-effect on quantifying the reaction intermediates on the surface of electrocatalysts with a rotating ring-disk electrode, we studied the formation of hydrogen peroxide in the oxygen reduction reaction on Pt/C with various sample loadings and then proposed an extrapolation model for measuring the intrinsic yield of H2O2, which can quantitatively reflect the characteristics of the surface of a given catalyst. In the extrapolation model, the catalyst loading effect can be compensated by taking the catalyst loading-dependent probability of the re-adsorption+further reaction of the desorbed H2O2 into consideration. The core concept in this extrapolation model is that the probability of the re-adsorption+reaction of the desorbed H2O2 becomes zero if there is no other active site available (i.e., at the extrapolated hypothetical point of zero catalyst loading) for re-adsorption of the desorbed H2O2. The intrinsic yield of H2O2 by extrapolation was much higher than that measured by the conventional model, in which the re-adsorption+reaction of the desorbed H2O2 is not considered, and thus the catalyst loading-dependent apparent yield of H2O2 does not properly reflect the intrinsic characteristics of the surface of a given catalyst. [Copyright &y& Elsevier]

Efficient nonprecious electrocatalysts with fast kinetics for the the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical to improve the efficiency of electrochemical systems such as fuel cells and metal-air battereies. Here, Co 9 S 8 embedded in porous nitrogen-doped carbon (N-C) matrix has been designed and fabricated. The as-fabricated Co 9 S 8 /N-C hybrid shows an excellent ORR activity, which is comparable to that of the commercial Pt/C (20 wt.%). Notably, the OER activity of Co 9 S 8 /N-C hybrid is superior to that of the RuO 2 /C (20 wt.%), a benchmark electrocatalyst for OER. The stabilities of Co 9 S 8 /N-C hybrid toward ORR and OER are significantly improved as compared to that of Pt/C (20 wt.%) and RuO 2 /C (20 wt.%), respectively. The synergistic effect of the covalent coupling between Co 9 S 8 and N-C and the porous structure of N-C is responsible for the enhanced catalytic activity and durability of Co 9 S 8 /N-C hybrid. [ABSTRACT FROM AUTHOR]