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Bi-metallic silver-copper nanoparticles were synthesized using two modes of combustion synthesis, known as Solution Combustion Synthesis (SCS) and Second Wave Combustion Synthesis (SWCS) to enhance surface alloying in Cu and Ag. The alloying in Ag and Cu nanoparticles was found to affect the adsorption of the oxygen molecule and synergistically increases the relative activity towards ORR and OER in 1 M KOH medium. The catalyst sample AgCu-21, synthesized by the SWCS showed highest activity and stability due to high concentration of Ag-Cu alloy on surface as verified by XPS, TEM and phase mapping of elements on the surface. The ORR catalyzed by AgCu-21 proceed through an overall four-electron pathway with a kinetic current density of 12.4 mA cm?2 at ?0.2 V potential. The XPS analysis of the samples indicates that the ORR and OER activity correlate well with the shifting in binding energy of Ag on Cu surface with higher degree of alloying resulting in better electrocatalytic performance. - 2019 Elsevier B.V. This publication was made possible by NPRP grant ( NPRP8-145-2-066 ) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the author(s). The authors also wish to gratefully acknowledge the Gas Processing Centre (GPC) and Central Laboratory Unit (CLU) at Qatar University, and Qatar Environment and Energy Research Institute (QEERI) at Qatar Foundation for services related to XPS, SEM/TEM and STEM-HAADF-EDS analyses, respectively. Appendix A Scopus

Simple and modified synthesis route for preparation of Fe-N/C type oxygen reduction reaction (ORR) catalysts has been worked out and discussed. The significant effect of the N precursor chemical composition on the ORR activity in 0.1 M KOH and 0.1 M HClO4 electrolyte solutions has been demonstrated. The half-wave potential values increased in the following order: C(SiC)

A Pt{110}-(1×1) single-crystal electrode surface was created by flame annealing and cooling of the electrode in gaseous CO. For the first time, the voltammetry of this unreconstructed surface is reported using aqueous perchloric acid and sodium hydroxide electrolytes. The voltammetric response for Pt{110}-(1×1) produces marked differences when compared with the reconstructed, H2- and N2-cooled, disordered Pt{110}-(1×2) surface phases. Pt{110}-(1×1) exhibits as many as 6 individual peaks in the low potential region (0–0.25V vs. Pd/H), a singular sharp oxidation peak at 0.95V (Pd/H) corresponding to the electrosorption of oxide and almost zero current associated with OH formation between 0.6V (Pd/H) and 0.9V (Pd/H). Charge density curves indicate that the total charge passed between 0V (Pd/H) and 1.5V (Pd/H) to be almost identical for both the (1×1) and the disordered (1×2) phases in perchloric acid, sulphuric acid and sodium hydroxide electrolyte. The oxygen reduction reaction (ORR) activity of the (1×1) surface phase was also examined using rotating disc electrode voltammetry in the hanging meniscus configuration. The half-wave ORR peak potential was found to be ∼30mV more negative than for the disordered reconstructed surface. This leads to the conclusion that the activity of the unreconstructed basal planes of platinum towards the ORR follows the order {100}

The mechanism of the oxygen reduction reaction (ORR) at a liquid|liquid interface, employing ferrocene (Fc) derivatives – such as decamethylferrocene (DMFc) – as a lipophilic electron donor along with sulfuric acid as an aqueous proton source, was elucidated through comparison of experimentally obtained cyclic voltammograms (CVs) to simulated CVs generated through COMSOL Multiphysics software which employs the finite element method (FEM). The simulations incorporated a potential dependent proton transfer (i.e . ion transfer, IT) step from the water (w) to organic (o) phases along with two homogeneous reactions (C1C2) occurring in the organic phase – an IT-C1C2 mechanism. The reaction of DMFc with H+(o) to form DMFc-hydride (DMFc-H+) was considered the first step (reaction 1), while reaction of DMFc-H+ with oxygen to form a peroxyl radical species, View the MathML sourceHO2, and DMFc+ was deemed the second step (reaction 2). Subsequent reactions, between View the MathML sourceHO2 and either DMFc or H+, were considered to be fast and irreversible so that 2 was a ‘proton-sink’, such that further reactions were not included; in this way, the simulation was greatly simplified. The rate of 1, kcf, and 2, kchem, were determined to be 5 × 102 and 1 × 104 L mol−1 s−1, respectively, for DMFc as the electron donor. Similarly, the rates of biphasic ORR for 1,1′-dimethylferrocene (DFc) and Fc were considered equivalent in terms of this reaction mechanism; therefore, their rates were determined to be 1 × 102 and 5 × 102 L mol−1 s−1 for 1 and 2, respectively. The reactive and diffusive layer thicknesses are also discussed.

Concentric microring-disk tips for scanning electrochemical microscopy (SECM) were fabricated and used in a new “tip generation–substrate collection–tip collection” (TG–SC–TC) mode to determine the activity of an Au electrocatalyst for the oxygen reduction reaction (ORR), while simultaneously monitoring hydrogen peroxide produced during the reaction. ORR electrocatalysis/hydrogen peroxide detection measurements were performed by evolving O 2 at the Au microring of the SECM tip while it was positioned close to an Au substrate. The O 2 diffused to the Au substrate where it was reduced generating a substrate current. At the same time, hydrogen peroxide generated during the ORR was detected by oxidation at the SECM tip microdisk. The effects of the microring current, the tip-substrate distance and the substrate potential during the TG–SC–TC experiment have been determined and are described. The ability to use these SECM tips to scan electrocatalyst surfaces while generating maps containing electrocatalytic and mechanistic data is then demonstrated and the prospects for the use of these SECM tips in screening arrays of ORR electrocatalysts discussed.

The oxygen reduction reaction was studied in 0.5 mol dm −3 HClO 4 solution on an electrode based on Ebonex-supported platinum electrocatalyst applied on rotation Au disk electrode (Au/Ebonex/Pt). Pt catalyst was prepared by impregnation method from 2-propanol solution of Pt(NH 3 ) 2 (NO 2 ) 2 and Ebonex powder. Ebonex support (non-stoichiometric mixture of titanium oxides) was characterized by: X-ray diffraction, energy dispersive X-ray spectroscopy and BET techniques. The synthesized catalyst was analysed by TEM technique. The kinetics of oxygen reduction reaction on the Ebonex/Pt catalyst shows a significant enhancement in comparison with the same on polycrystalline Pt. Only a single Tafel slope of −0.106 V dec −1 is observed and the first-rate determining step in direct four-electron reduction is proposed as a main partway in the whole range of potential. The absence of PtOH layer, that inhibits oxygen reduction on polycrystalline Pt, was discussed through synergetic effect into the catalyst as a consequence of the interactions of Pt nanoparticles with Ebonex, on one hand, and, through the d-band coupling model where the surface reactivity is given by the energy shift of the surface d-states with respect to the Fermi level, on the other hand.