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Abstract: Up to now, it remains to be a challenge to accurately and reproducibly evaluate the oxygen reduction reaction (ORR) activity by a thin-film rotating disk electrode (TF-RDE) and results in literatures often disagree. In this work, we developed an “intermittently microcontact-coating fine-droplets” method of preparing homogeneous thin-film to guarantee the accuracy of electro-catalytic activity evaluation by a TF-RDE, in which the measured electrode current is controlled by both the diffusion of the reactant from the electrolyte bulk to the surface of the electro-catalyst and the kinetic process on the surface of the electro-catalyst. By precisely controlling the distribution and varying the loading of nano-sized Pt/C particles on a smooth glassy carbon substrate with an in-house-developed automated electrode-preparation device, we investigated the effect of the distribution of the particles on the accuracy of compensating for diffusion limitations of ORR in an aqueous acid solution. As a reference, a smooth Pt bulk disk electrode was evaluated under the same environment to clarify the effect of the within-thin-film diffusion, which may occur in the TF-RDE. The results show that, the accuracy of correction for diffusion limitations cannot be guaranteed by only a linear relation of 1/I versus (rotation rate)−1/2 in Koutecky–Levich plot and significantly depends on the distribution of the particles on the substrate. Some criteria for judging the accuracy of the compensation and optimization of the thin-film structure have been systematically discussed. [Copyright &y& Elsevier]

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]

Both Al and Ga have exhibited excellent performance, respectively, for the An/Ln separation based on molten salt electrolysis, and the Al-Ga composite cathode may have superior properties. Therefore, in this work, the electrochemical behaviors of Ce (III) on the binary Al-Ga electrode were systematically explored by co-reduction of Ce (III), Al (III) and Ga (III) on a W electrode. A new oxidation signal of Al 2 Ga 2 Ce ternary intermetallic compound was successfully detected. In addition, for comparison, the co-reduction behaviors of Ce (III) with Al (III) and Ce (III) with Ga (III) on an inert tungsten electrode were also investigated. The results showed that different kinds of alloys are formed on the surface of W electrode. Finally, several typical Ga-Ce and Al-Ga-Ce intermetallic compounds were obtained by potentiostatic electrolysis and the deposited products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS). [ABSTRACT FROM AUTHOR]

Abstract Under over-increasing demand of advanced lithium-ion batteries (LIBs) for long-range electric vehicles (EVs), high-capacity transition metal oxide (TMO) negative electrodes for LIBs are thought as potential substitutes of traditional graphite anodes. A major barrier for TMO anodes is volumetric expansion during lithiation processes, leading to active material pulverization and falling off current collectors, which seriously deteriorates capacity retention. Herein, apart from conventional mechanical degradation, another capacity fading mechanism is revealed. Furthermore, the understanding is supported by an interesting cycling property. Firstly, NiCo 2 O 4 with designed morphologies of nanoplates and microspheres are studied for the initial (de)lithiation and prolonged cycles. The morphology changes indicate solid electrolyte interphase (SEI) layer accumulating on the surface of electrodes and impeding the contact and reactions between lithium and active materials with a result of severe capacity loss. It can be understood as SEI layer insulating NiCo 2 O 4 , and if SEI film appropriately changes, high capacities can recovery. This conjecture is confirmed by following research of NiCo 2 O 4 nanoparticles with amazing cycling performance prepared by a facile water-bath method. As LIB anodes, NiCo 2 O 4 nanoparticles exhibit capacities of 1144 mAh g−1 at the initial discharging, 230 mAh g−1 at the 100th cycle and 661 mAh g−1 at the 500th cycle. The corresponding coulombic efficiency is of 73.1%, 98.4% and 99.5%, respectively. By TEM characterization in combination with electrochemical analysis, size-dependent SEI layer reactivation (from thick and unstable to thin and stable) is a key role on the dramatic capacity recovery. [ABSTRACT FROM AUTHOR]

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]

The spinel-type MnCo 2 O 4 is an attractive bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, the catalytic activity of MnCo 2 O 4 is limited by its poor electronic conductivity. Herein MnCo 2 O 4 coated with conducting polypyrrole (i.e. MCO@PPyhybrid) is synthesized. The obtained MCO@PPy hybrid exhibits excellent electrocatalytic activity for both the ORR and OER, outperforming pristine MCO, PPy and MCO+PPy mixture. The ORR and OER activities of MCO@PPy are comparable to that of the commercial Pt/C (20 wt.%) and RuO 2 /C (20 wt.%), benchmark electrocatalysts for ORR and OER, respectively. While the stabilities of MCO@PPy hybrid toward both the ORR and OER are much higher than that of Pt/C (20 wt.%) and RuO 2 /C (20 wt.%), respectively. The PPy coating on the surface of MCO provides a conductive network for fast electron transfer and the coupling between the PPy layer and MCO promotes the transfer of electrons from PPy to MCO, benefiting the ORR and OER. The results reveal the effectiveness of surface modification with conducting polymer on improving the electrocatalytic activity of spinel oxide. [ABSTRACT FROM AUTHOR]