[en] Two gold nanorod-polyaniline (Au-PANI) composites with different contents of Au were prepared by two methods. An ex situ method, in the presence of preformed gold nanorods (AuNRs) and in situ one, when an AuNRs and PANI matrix is produced simultaneously, were used. Both methods were performed in immiscible water/toluene biphasic system as a simple interfacial polymerization process. Optical, structural and morphological characteristics of the formed nanocomposites were identified. It was found that AuNRs are embedded in the conducting emeraldine salt form of PANI. Nanocomposites containing 2.0 and 28.9 wt% of Au were subsequently systematically studied for borohydride oxidation reaction (BOR) for potential application in direct borohydride-peroxide fuel cell (DBPFC). Reaction parameters: number of electrons exchanged, order of reaction and activation energy, were evaluated. Both Au-PANI nanocomposites showed activity for BOR. A laboratory DBPFC was tested reaching specific peak power density of 184 Wg(-1) at 65 degrees C with Au-PANI 1 nanocomposite (containing only 2.0 wt% of Au) as anode.

[en] This work shows the potential application of carbon materials prepared by three different ionic liquid-based methods, using 1-butyl-3-methylimidazolium methanesulfonate [bmim][MeSO3], for electrochemical supercapacitors. The effects of [bmim][MeSO3] on morphology, texture and surface chemistry of prepared materials has been explored by SEM/TEM, N2/CO2 adsorption measurements and XPS. The results indicate the possibility of synthesis of carbon materials with tunable physicochemical properties using ionic liquid based methods. The charge storage behavior of all materials was studied in three different pH aqueous electrolytes. The pseudocapacitive and double layer contributions were estimated and discussed from the aspect of the textural changes and the changes of the chemical composition of surface functional groups containing heteroatoms. C[dbnd]O type functional groups, with the contribution of COOH groups, were found to be responsible for a different amount of charge, which could be stored in alkaline and acidic electrolytic solution. The material prepared by direct carbonization of [bmim][MeSO3], showed the best electrochemical performance in alkaline electrolyte with a capacitance of 187 F g−1 at 5 mV s−1 (or 148 F g−1 at 1 A g−1), due to the contribution of both electric-double layer capacitance and pseudocapacitance which arises from oxygen, nitrogen and sulfur functional groups. © 2018 Elsevier Ltd

[en] The development of highly active and inexpensive electrode materials is crucial to improve the performance of fuel cells and to boost their commercialisation. In this work, a series of bimetallic palladium alloy nanoparticles assembled on reduced graphene oxide, namely PdFe/rGO, PdAg/rGO and PdAu/rGO, was prepared and tested for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) in alkaline media. The morphology and structure of the as-prepared PdM alloy NPs and PdM/rGO electrocatalysts were characterised by XRD, TEM, XPS and ICP-MS and their electrochemical activity was investigated by cyclic and linear scan voltammetry, chronoamperometry, and rotating disc electrode measurements. Among the tested electrocatalysts, PdAu/rGO demonstrated the best performance by providing high current densities for both ORR and BOR. The number of electrons exchanged during ORR at PdAu/rGO, PdAg/rGO and PdFe/rGO electrocatalysts was calculated to be 4.0, 2.8 and 2.0, whereas Tafel slopes were evaluated to be 0.202, 0.182 and 0.173 V dec⁻¹, respectively. BOR at PdAu/rGO and PdFe/rGO proceeds with 5.5 and 2 electrons exchanged, respectively, and the reaction order ranged from 0.4 for PdAg/rGO to 1 for PdAu/rGO. Furthermore, effect of temperature was studied and BOR activation energy determined to be 23 kJ mol⁻¹. - Graphical abstract: Bimetallic palladium alloy nanoparticles anchored on reduced graphene oxide support, PdFe/rGO, PdAg/rGO and PdAu/rGO, are tested for both cathode and anode reactions of the direct borohydride fuel cell. PdAu/rGO reveals high activity and the highest number of exchanged electrons for both ORR and BOR. - Highlights: • PdM alloy NPs were successfully prepared and anchored on reduced graphene oxide. • PdM/rGO displayed good electrocatalytic activity for ORR and BOR in alkaline media. • Higher ORR and BOR current densities were obtained for PdAu/rGO.

[en] Highlights: • Gold-rare earth (RE = Sm,Dy,Ho,Y) alloys are prepared by arc or induction melting. • Four Au-RE alloys are active for BOR, with Au-Y showing the highest activity. • BOR at Au-Y alloy proceeds as a 1st order reaction with a low E_a of 20.2 kJ mol⁻¹. • A peak power density of 215 mW cm⁻² is obtained for DBPFC with Au-Y anode at 45 °C. -- Abstract: Gold-rare earth (Au-RE) alloys with equiatomic compositions are prepared by arc (RE = Dy, Ho, Y) or induction (RE = Sm) melting. Morphology and phase composition is assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDXS), while X-ray powder diffraction (XRPD) is used to confirm crystal structures. The Au-RE electrodes are evaluated for borohydride oxidation reaction (BOR) in alkaline media employing cyclic voltammetry and chronoamperometry. The obtained data allows calculation of kinetic parameters that characterize the borohydride (BH₄^-) oxidation at Au-RE alloys, including the number of exchanged electrons, n, and the anodic charge transfer coefficient, α. n values range from 2.4 to 4.4, while α values are found to be in the 0.60–0.83 range. The BOR apparent activation energy, E_a^app, and the reaction order, β, are also determined from CV data obtained at different temperatures and different BH₄^- concentrations, respectively. Low E_a^app values range from 16.4 (Au-Sm) to 20.2 kJ mol⁻¹ (Au-Y) and β values suggest that BOR at the examined alloys is a 1st order reaction with respect to BH^-₄ concentration. A small-scale direct borohydride-peroxide fuel cell (DBPFC) operating with Au-Y anode at 25 °C reaches a peak power density of 150 mW cm⁻². The cell performance is enhanced when increasing the temperature to 45 °C, with a maximum power density of 215 mW cm⁻² being attained.

[en] Carbon-supported silver nanoparticles (Ag:NPs/C) were synthesized by gamma irradiation-induced reduction method using the poly(vinyl alcohol) or poly(vinyl alcohol)/chitosan polymer as stabilizer. Prepared samples were characterized using transmission electron microscopy and X-ray diffractometry. Subsequently, Ag:NPs/C were studied using rotating disc and rotating ring disc method as electrocatalysts for ORR (oxygen reduction reaction) and BOR (borohydride oxidation reaction) for potential application in alkaline fuel cells. The synthesis method used herein offers simple and fast approach for catalytic ink preparation, since the ink is prepared in one-step radiation process, simultaneously with Ag"+ ions reduction. Very high and stable catalytic efficiency toward ORR via 4e"− path was evidenced during 4000 square pulse polarization cycles. BOR, accompanied with the simultaneous borohydride ion hydrolysis, was found to proceed at the oxidized Ag surface. - Highlights: • Ag nanoparticle electrocatalysts synthesized via γ-irradiation method. • The synthesis procedure offers greatly simplified in-situ catalytic ink preparation. • Ag electrocatalysts tested for oxygen reduction and borohydride oxidation. • Oxygen reduction proceeds as 4e"− process with high kinetic currents. • Borohydride hydrolysis is catalyzed parallel with its oxidation.

[en] Highlights: • Carbonized PANIs prepared from various nanostructured PANI precursors • Electroanalytical performances of carbonized PANIs evaluated using voltammetry • Study of carbonized PANIs physico-chemical properties related to electroactivity • The lowest over-potential for NO₂⁻ oxidation at c-PANI (+0.87 V vs. SCE) • The lowest over-potential for ascorbic acid oxidation at both c-PANI and c-PANI-SSA - Abstract: A comparative study of the electrocatalytic activity of nitrogen-containing carbon nanomaterials, prepared by the carbonization of nanostructured polyaniline (PANI) salts, for the electrooxidation reactions is presented. Nanostructured PANI salts were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous solution in the presence of 5-sulfosalicylic acid (PANI-SSA), 3,5-dinitrosalicylic acid (PANI-DNSA) as well as without added acid (PANI), and subsequently carbonized to c-PANI-SSA, c-PANI-DNSA and c-PANI, respectively. Glassy carbon tip was modified with nanostructured c-PANIs and used for the investigation of sensing of nitrite and ascorbic acid in aqueous solutions as model analytes by linear sweep voltammetry. All three types of the investigated c-PANIs gave excellent response to the nitrite ions and ascorbic acid electrooxidation. The lowest peak potential for nitrite ion oxidation exhibited c-PANI (+0.87 V vs. SCE), and for ascorbic acid oxidation both c-PANI and c-PANI-SSA (ca. + 0.13 V vs. SCE). Electrochemical data were correlated with structural and textural data obtained by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, elemental and nitrogen sorption analysis

[en] Highlights: • PdX was obtained by Pd ion exchange with Na ion in NaX zeolite. • PdX maintained the original crystallinity and morphology of NaX. • PdX exhibited high activity for borohydride oxidation with up to 5 electrons exchanged. • Reaction order close to 1 was evaluated. • DBPFC with PdX anode showed excellent performance with power density of 263 mW cm⁻². This work proposes a direct borohydride fuel cell (DBFC) with palladium (Pd)-impregnated faujasite X zeolite (PdX) as anodic electrocatalyst. The PdX was prepared by Pd ion exchange with Na ion within NaX zeolite and it was characterised by ICP-OES, FTIR, SEM-EDS, TEM and N₂ sorption analysis. PdX was subsequently tested as electrocatalyst for borohydride (BH₄⁻) oxidation reaction (BOR) using linear scan voltammetry with and without electrode rotation. For this purpose, sodium borohydride (NaBH₄) solutions ranging between 0.01 and 0.06 M in alkaline medium were used. The reaction order for BH₄⁻ oxidation at PdX was determined to be close to 1. The PdX zeolite electrode showed high performance for BOR, as evidenced by 3–5 electrons exchanged, depending on NaBH₄ concentration. A laboratory direct borohydride-peroxide fuel cell was assembled using a PdX anode and tested in the 25–45 °C temperature range, reaching power densities between 214 and 263 mW cm⁻².

[en] Highlights: • Pd ion-exchanged zeolite X is used for hydrogen evolution reaction electrocatalysis. • PdX was analysed by ICP-OES, XRD, SEM and conductivity measurements. • XRD analysis revealed presence of PdO on the outer surface of zeolite. • PdX activity for HER is systematically evaluated by CV, CA, and EIS studies. • DFT study correlated hydrogen adsorption on PdO layer with HER catalytic activity. - Abstract: Palladium ion-exchanged zeolite X (PdX) was prepared by zeolite impregnation with palladium acetylacetonate, followed by thermal degradation of the salt. PdX was characterised using SEM-EDS, ICP-OES and XRD. Analysis revealed presence of 7.78 wt.% of Pd in the form of PdO. Subsequently, PdX was tested for hydrogen evolution reaction (HER) in alkaline medium using linear scan voltammetry, chronoamperometry and electrochemical impedance spectroscopy measurements. The influence of addition of carbon black on the material's catalytic performance was also investigated. The HER kinetic parameters, including Tafel slope, exchange current density and activation energy, were determined. In order to provide atomic-level insights, experimental results were complemented by density functional theory calculations. It is suggested that favourable hydrogen adsorption energetics on PdO is responsible for efficient HER catalysis by this novel electrocatalyst.