Search

Polarization curves and complex kinetics of oxygen reduction (ORR) and borohydride oxidation (BOR) reaction were evaluated at thin Au layer on Ti and TiO2 electrodes. TiO2 electrodes prepared included amorphous TiO2 (AM−TiO2) and anatase (A−TiO2). The electrodes structure and nanotube arrays morphology were observed by XRD and SEM, respectively. All electrodes show activity for both ORR and BOR. The use of Au layer over A−TiO2 produces the strongest synergistic effect for ORR with exchange of 3 electrons. On the other hand, the strongest effect for BOR was observed in case of Au/Ti. [ABSTRACT FROM AUTHOR]

Abstract: Carbon materials, prepared by using different methods with ionic liquids, are compared as electrocatalysts for the oxygen reduction reaction (ORR). Materials were synthesized through the hydrothermal carbonization of glucose and by using the same method in the presence of 1‐butyl‐3‐methylimidazolium methanesulfonate [bmim][MeSO3] as an additive. Another two carbon‐based materials were prepared by using ionic‐liquid‐based methods: ionothermal carbonization of glucose using [bmim][MeSO3] as a recyclable medium for the carbonization reaction and by direct carbonization of the ionic liquid in a one‐step method using [bmim][MeSO3] as the precursor for N‐ and S‐doped porous carbon (Carb‐IL). Characterization results showed the possibility of morphology and porosity control by using [bmim][MeSO3]. All materials were subsequently tested for the ORR in alkaline media. Carb‐IL showed enhanced and stable electrocatalytic ORR activity, even in the presence of methanol, ethanol, and borohydride, opening the possibility for its application in fuel cells. [ABSTRACT FROM AUTHOR]

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 . [ABSTRACT FROM AUTHOR]

Palladium-nickel nanoparticles supported on different tin oxide-carbon composites, namely PdNi/(SnO 2 -KB600), PdNi/(SnO 2 -KB300) and PdNi/(SnO 2 -graphene), as well as on Vulcan XC-72 (PdNi/Vulcan), are prepared and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The electrocatalytic activity of each material for the oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) is studied in alkaline media by voltammetric techniques using rotating disk electrode (RDE) and rotating ring disk electrode (RRDE). ORR and BOR parameters, such as number of exchanged electrons, kinetic current density, Tafel slope and activation energy, are calculated. ORR n values at 0.2 V are close to 4 for PdNi/(SnO 2 -KB600) and PdNi/Vulcan, and close to 2 for PdNi/(SnO 2 -KB300) and PdNi/(SnO 2 -graphene). BOR n values range from 1.9 for PdNi/(SnO 2 -graphene) to 3.4 for PdNi/(SnO 2 -KB300). The materials stability is examined by chronoamperometry. The obtained results show that PdNi nanoparticles anchored on SnO 2 -KB600 support are good electrocatalyst candidates for both ORR and BOR in alkaline media. [ABSTRACT FROM AUTHOR]

Designing highly active and cost-effective electrocatalysts is essential for accelerating commercialization of fuel cell technology. In this work, oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) are both investigated on monodisperse palladium nanoparticles (Pd NPs) supported on Vulcan XC72 as well as on two prepared carbon materials obtained from different biosources, namely grape stalk activated carbon (GSAC) and vine shoots activated carbon (VSAC). The electrocatalysts are characterized using TEM and XRD and their activity for ORR and BOR in alkaline media is studied using linear scan voltammetry with rotating ring-disk electrode. ORR and BOR onset potentials and number of exchanged electrons reveal significantly higher activity of the Pd NPs supported on biobased carbons compared to the one supported on Vulcan XC72. Pd/GSAC shows good activity towards direct 4-electron ORR, whereas Pd/VSAC electrocatalyst has improved performance for BOR. Namely, number of exchanged electrons in ORR at Pd/GSAC and Pd/VSAC was evaluated to be approximately 4 and 2, respectively. Conversely, number of exchanged electrons in BOR was found to be 2.0 and 5.6 for Pd/GSAC and Pd/VSAC, respectively. [ABSTRACT FROM AUTHOR]

The electrochemical oxidation of sodium borohydride (NaBH 4 ) is systematically studied on platinum–dysprosium (Pt–Dy) alloys in alkaline media with respect to application in direct borohydride fuel cells (DBFCs). Using several different techniques, namely cyclic voltammetry, chronoamperometry and chronopotentiometry, reaction parameters are evaluated for NaBH 4 electrooxidation in 2 M NaOH supporting electrolyte. The values obtained for the number of electrons exchanged are comparable for the two alloys and close to 2.5. Dependence of Pt–Dy alloys activity for NaBH 4 oxidation on the electrolyte composition and temperature is also investigated. Test fuel cell is assembled using Pt–Dy alloy as anode, reaching peak power density of 298 mW cm −2 at current density of 595 mA cm −2 and cell potential of 0.5 V at 25 °C. Pt–Dy alloys exhibit comparable behavior with pure Pt electrode at room temperature, while at higher temperature they exhibit improved Coulombic efficiency, with the advantage of significantly lower price. [ABSTRACT FROM AUTHOR]

The synthesis of palladium-based trimetallic catalysts via a facile and scalable synthesis procedure was shown to yield highly promising materials for borohydride-based fuel cells, which are attractive for use in compact environments. This, thereby, provides a route to more environmentally friendly energy storage and generation systems. Carbon-supported trimetallic catalysts were herein prepared by three different routes: using a NaBH4-ethylene glycol complex (PdAuNi/CSBEG), a NaBH4-2-propanol complex (PdAuNi/CSBIPA), and a three-step route (PdAuNi/C3-step). Notably, PdAuNi/CSBIPA yielded highly dispersed trimetallic alloy particles, as determined by XRD, EDX, ICP-OES, XPS, and TEM. The activity of the catalysts for borohydride oxidation reaction was assessed by cyclic voltammetry and RDE-based procedures, with results referenced to a Pd/C catalyst. A number of exchanged electrons close to eight was obtained for PdAuNi/C3-step and PdAuNi/CSBIPA (7.4 and 7.1, respectively), while the others, PdAuNi/CSBEG and Pd/CSBIPA, presented lower values, 2.8 and 1.2, respectively. A direct borohydride-peroxide fuel cell employing PdAuNi/CSBIPA catalyst in the anode attained a power density of 47.5 mW cm−2 at room temperature, while the elevation of temperature to 75 °C led to an approximately four-fold increase in power density to 175 mW cm−2. Trimetallic catalysts prepared via this synthesis route have significant potential for future development. [ABSTRACT FROM AUTHOR]

Gold polypyrrole (AuPPy) and copper polypyrrole (CuPPy) nanocomposites were prepared by a simple one-step in situ oxidative polymerization of pyrrole monomer by Au3+ and Cu2+ ions. Owing to their characteristic physicochemical properties confirmed by optical and structural characterization methods, the behavior of these materials as electrocatalysts for borohydride oxidation reaction (BOR) was considered. BOR apparent activation energy was found to be 16 and 22 kJ mol−1 for AuPPy and CuPPy electrocatalyst, respectively. The stability of the two electrocatalysts was assessed by chronoamperometry. Moreover, fuel cell tests were carried out with AuPPy and CuPPy as anode electrocatalyst of a direct borohydride-peroxide fuel cell (DBPFC). Open circuit voltage (OCV) of 1.30 V was obtained with both AuPPy and CuPPy, with the OCV increasing to 1.45 V upon adding a small amount of carbon (AuPPy-C). The peak power density of a DBPFC with BOR at AuPPy-C anode and hydrogen peroxide reduction reaction at Pt cathode was found to be ca. 162 mW cm−2 at 65 °C. [Display omitted] • Two stable nanocomposites, AuPPy and CuPPy, were synthesized by in situ method. • AuPPy and CuPPy exhibit electrocatalytic activity for borohydride oxidation. • AuPPy exhibits higher BOR activity with low activation energy. • π-conjugated PPy form in composites has better doping level through AuPPy matrix. • DBFC by BOR at AuPPy-C anode and H 2 O 2 reduction at Pt cathode reaches 162 mWcm−2 at 65 °C. [ABSTRACT FROM AUTHOR]

Polypyrrole-carbon (PPy-C) composites having different amounts of carbon (5–35 wt.%) decorated with platinum nanoparticles (Pt/PPy-C) were prepared and investigated for borohydride oxidation reaction (BOR) in alkaline medium and for hydrogen peroxide reduction reaction (HPRR) in acidic medium. Structural and morphological properties and composition of these electrocatalysts were determined by FTIR, Raman, XPS, SEM/EDS, TEM and ICP-MS analyses. Pt/PPy-C electrocatalysts were evaluated for BOR and HPRR by cyclic voltammetry and chronoamperometry. Faradaic and kinetic parameters, such as the number of exchanged electrons, n, charge transfer coefficient, α, apparent activation energy, E a app , and order of reaction, β, were calculated. n for BOR ranged from 6.0 to 7.6, while n for HPRR ranged from 1.0 to 2.0. E a app was found to range from 10 to 18 kJ mol −1 for BOR and from 8 to 14 kJ mol −1 for HPRR. The BOR was found to be a 1st order reaction with respect to BH 4 − . Pt/PPy-C 35% electrocatalyst showed the best activity for both reactions. Fuel cell tests were done with Pt/PPy-C electrodes as anode, as cathode and as both anode and cathode in a direct borohydride-peroxide fuel cell (DBPFC). DBPFC with Pt/PPy-C 35% as anode electrocatalyst gave the highest peak power density of 1432 W g Pt −1 at current density of 2046 A g Pt −1 and cell voltage of 0.70 V. [ABSTRACT FROM AUTHOR]

5 nm palladium nanoparticles (Pd NPs) are synthesized and assembled on reduced graphene oxide-iron oxide nanocomposite (rGO-Fe 3 O 4 ) to be used in oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) studies in alkaline media. The structure and morphology of the resulting Pd/rGO-Fe 3 O 4 hybrid material are evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) analyses. The electrochemical behavior of Pd/rGO-Fe 3 O 4 hybrid material for the ORR and BOR is investigated by voltammetry with rotating disk and rotating ring disk electrode and electrochemical impedance spectroscopy, enabling evaluation of the number of exchanged electrons, Tafel slope, exchange current density and activation energy. The results reveal that ORR at Pd/rGO-Fe 3 O 4 proceeds as a 2-electron process with Tafel slope of 0.133 V dec −1 , while BOR proceeds as a 5.6-electron process with Tafel slope of 0.350 V dec −1 and exchange current density of 1.38 mA cm −2 . The BOR activation energy was found to be 12.4 kJ mol −1 . Overall, this study demonstrates the good efficiency of Pd/rGO-Fe 3 O 4 hybrid material for BOR. [ABSTRACT FROM AUTHOR]

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 N 2 sorption analysis. PdX was subsequently tested as electrocatalyst for borohydride (BH 4 − ) oxidation reaction (BOR) using linear scan voltammetry with and without electrode rotation. For this purpose, sodium borohydride (NaBH 4 ) solutions ranging between 0.01 and 0.06 M in alkaline medium were used. The reaction order for BH 4 − 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 NaBH 4 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 . [ABSTRACT FROM AUTHOR]

• In situ polymerisation is used to produce Ag-polyaniline-polyvinylpyrrolidone composites. • Ag-PANI-PVP nanocomposites exhibit electrocatalysis of borohydride oxidation. • Optimum Ag content determined to be 35.4 wt.% results in low activation energy of BOR. • 35.4 wt.%Ag -PANI-PVP delivers the highest current density and specific current density. The catalytic activity of five silver-polyaniline-polyvinylpyrrolidone (Ag@PANI@PVP1–5) nanocomposites for borohydride oxidation reaction (BOR) was thoroughly examined. The nanocomposites were synthesized by an in situ chemical oxidative polymerization of aniline monomer by Ag+ ions in the presence of accelerator – PVP and physicochemical properties were determined prior their use in electrocatalysis. Ag@PANI@PVP3 with 35.4 wt% Ag delivered the highest current density and specific current density during BOR. Evaluation of the order of reaction < 1 suggested indirect BOR mechanism. Furthermore, Ag@PANI@PVP3 also delivered the highest current density and stable performance during chronoamperometric study of BOR. Its apparent activation energy of 15 kJ mol−1 was found to be the lowest among the studied materials accounting for the high current densities. [Display omitted] [ABSTRACT FROM AUTHOR]

Carbon-supported palladium nanoparticle electrocatalysts were prepared using two different carbon supports, commercial Vulcan ® XC72 (Pd/Vul) and synthesized carbonized nanostructured polyaniline doped with 3,5-dinitrosalicylic acid (Pd/c-PANI), and using two different synthesis procedures. Morphology and Pd content for each of the four electrocatalysts were determined using transmission electron microscopy and thermogravimetric analysis, respectively. The electrocatalysts were further analyzed electrochemically using cyclic voltammetry and linear scan voltammetry with a rotating ring–disc electrode, as well as chronoamperometry, considering their activity in direct borohydride/peroxide fuel cells, i.e., for the borohydride oxidation reaction (BOR) in alkaline media as well as for the hydrogen peroxide reduction reaction (HPRR) in acidic media. The number of electrons exchanged in BOR varied between 2.4 and 4.8, while unique n value of 2 was evidenced in HPRR. Activation energies for BOR at studied materials were in the 10.3–26.2 kJ mol −1 range and for HPRR in the 31.7–48.3 kJ mol −1 range. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (BH 4 -) 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 BH 4 - 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. ga1 • 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 FROM AUTHOR]