Direct Borohydride Research Articles

Gold-Cobalt Deposited on Titania Nanotubes as Anode Catalyst for Direct Borohydride Fuel Cells

In the present work gold-cobalt catalysts deposited on titania nanotubes surface (denoted as Au(Co)/TiO2-NTs) were investigated as anode material in direct borohydride fuel cells (DBFCs). The catalysts were prepared by a simple and cost-effective galvanic displacement technique [1]. At first, the sub-layer of Co was deposited on the titania nanotubes surface via electroless deposition. The gold crystallites were then deposited on the Co/TiO2-NTs electrodes by their immersion into gold(III)-containing solution for different time periods. It has been determined that the Au loadings were in the range from 10 to 60 µg cm–2 in the Au(Co)/TiO2-NTs catalysts. Field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDXS) were used to characterize the surface morphology and composition of the samples, respectively. The activity of the Au(Co)/TiO2-NTs catalysts for borohydride oxidation reaction (BOR) was evaluated by cyclic voltammetry and chronoamperometry measurements. The performance of a DBFC operating with 1 M NaBH4 + 4 M NaOH as fuel and 5 M H2O2 + 1.5 M HCl as oxidant, while employing Pt as the cathode catalyst and Au(Co)/TiO2-NTs with different Au loadings as the anode catalyst were investigated. Peak power densities up to 122 mW cm-2 were attained at 25 ºC. It was found that the highest specific peak power density of 9.6 kW g–1 Au was obtained when employing Au(Co)/TiO2-NTs with the Au loading of 10 µg cm–2as the anode catalyst.

In situ X-ray Diffraction Investigation of Hydrogen Storage Alloys During Charge and Discharge

Metal hydride electrodes have shown to be useful both in secondary batteries, e.g. the Ni/metal hydride system, and more recently in fuel cells, especially for direct borohydride fuel cells. This work provides in situ X-ray diffraction (XRD) results aiming at characterizing the phase transitions of the LaNi4.7Sn0.2Cu0.1 metal hydride alloy with and without Pt in the particle surface when charged electrochemically and chemically by exposition to a borohydride solution. Results have shown that the method of alloy charging leads to different phase predominance and different site occupancies, but both methods lead to almost the same discharge capacity. In the electrolysis process, ?-? phase transitions are predominant during the charge/discharge, while in the chemical charging by exposure to a borohydride solution the ?-? phase transition is more important, indicating occurrence of smaller localized stress in the alloy, with benefit on the material lifetime. Essentially the same phenomena were observed for the alloy with Pt, either with respect to the alloy structure and the electrochemical characteristics.

Pt-Ni Decorated Metal Oxide Electrodes for Borohydride Fuel Cells

Electrochemical energy conversion devices including fuel cells, batteries, and supercapacitors are expected to replace fossil-fuel based technologies in different applications. Direct borohydride fuel cells (DBFCs) are a type of alkaline fuel cells that use sodium borohydride (NaBH4) as a fuel and oxygen (O2) as an oxidant. DBFCs have several advantages over other types of fuel cells, from easier handling and cell management, to better cell performance, i.e. higher power densities [1]. Oxygen reduction reaction (ORR) is one of the most studied reactions in electrochemistry and, specifically, for electrochemical energy conversion, due to its application in fuel cells and metal–air batteries [2]. Sluggish kinetics of this reaction is one of the crucial restraining factors in the energy conversion efficiency of these devices. Namely, ORR proceeds at high overpotential and includes several steps [3,4]. Though ORR in alkaline media has faster kinetics compared to that in acid media, platinum (Pt) is still the most frequently employed electrocatalyst even in alkaline fuel cells. Borohydride (BH4 -) oxidation reaction (BOR) is normally accompanied by BH4 - hydrolysis so that the faradic efficiency of this reaction is reduced. So far, gold (Au) has been demonstrated as the only electrode material active for BOR and inactive for BH4 -hydrolysis. Still, Pt is among the most commonly used electrocatalysts for BOR due to the faster reaction kinetics at Pt compared to Au. Having in mind scarcity of Pt and, consequently, its high price, wide search for electrocatalysts with similar activity, but lower price is ongoing. One way to reduce amount of Pt is combining it with other active materials, such as transition metals [5]. Further reductions in the amount of Pt used in the electrocatalysts can be obtained by supporting smaller amounts of metal onto high-surface area supports. Herein, PtNi nanoparticles are decorated on different metal oxide supports, namely MnO2, MnO2+NiO and MnO2+TiO2. Then, the prepared samples are tested as electrocatalysts for both ORR and BOR in alkaline media. Dependence of electrocatalysts behavior on reaction conditions, namely fuel and oxidant concentrations, and electrolyte temperature was studied using voltammetric techniques. Reaction parameters, such as number of exchanged electrons, and reaction mechanism were evaluated using rotating disk and rotating ring disk electrode measurements. Finally, the stability of the prepared electrocatalysts was assessed using chronoamperometry. [1] B. Šljukić, J. Milikić, D.M.F. Santos, C.A.C. Sequeira, D. Macciò, A. Saccone, J. Power Sources 272 (2014) 335-343. [2] M.S. Dresselhaus, I.L. Thomas, Nature 414 (2001) 332-337. [3] I. Gatto, A. Stassi, E. Passalacqua, A.S. Aricò, Int. J. Hydrogen Energy 38 (2013) 675-681. [4] H. Dong, B. Lin, K. Gilmore, T. Hou, S.-T. Lee, Y. Li, J. Power Sources 299 (2015) 371-379. [5] B. Šljukić, J. Milikić, D.M.F. Santos, C.A.C. Sequeira, Electrochim. Acta 107 (2013) 577-583.

Nanostructured 3D metallic foams for H2O2 electroreduction

Direct borohydride fuel cells, which use sodium borohydride as the fuel, are recently focussing on the use of hydrogen peroxide as oxidant instead of the traditional oxygen gas. Herein we study the electrocatalytic activity of nanostructured 3D Cu-M (M = Fe, Co, Ni) and single metal Ni and Co foams for hydrogen peroxide reduction reaction (HPRR) in alkaline media. The electrode materials are prepared by galvanostatic electrodeposition and their morphology, composition and crystallographic structure are characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The electrochemical characterisation is performed by voltammetry and chronoamperometry measurements, where it is concluded that Cu–Fe and Cu–Ni foams exhibit good catalytic activity for HPRR with a number of electrons transferred during the reaction close to 1.

Modeling the effect of membrane conductivity on the performance of alkaline fuel cells

The present work proposes and demonstrates a methodology to capture the effect of operating conditions on ionic conductivity of membranes immersed in alkaline media. Based on reported experimental results for an anion exchange membrane (A-201 by Tokuyama) and a cation exchange membrane (Nafion 211), two novel expressions are developed for the ionic conductivity by incorporating the effects of solution concentration and temperature. The expression for the cationic conductivity is applied in a cell-level model to predict the performance of an alkaline direct borohydride fuel cell; it is found that the membrane ionic conductivity significantly affects the cell performance and capturing its functionality is essential to accurately predict the fuel cell performance.

Platinum-rare earth cathodes for direct borohydride-peroxide fuel cells

Hydrogen peroxide (H2O2) is being actively investigated as an oxidant for direct borohydride fuel cells. Herein, platinum-rare earth (RE = Sm, Dy, Ho) alloys are prepared by arc melting and their activity for hydrogen peroxide reduction reaction (HPRR) is studied in alkaline media. Cyclic voltammetry and chronoamperometry measurements show that Pt–Sm electrode displays the highest catalytic activity for HPRR with the lowest activation energy, followed by Pt–Ho, while Pt–Dy alloys show practically no activity. Laboratory direct borohydride-peroxide fuel cells (DBPFCs) are assembled using these alloys. The DBPFC with Pt–Sm cathode gives the highest peak power density of 85 mW cm−2, which is more than double of that obtained in a DBPFC with Pt electrodes.

Nickel–rare earth electrodes for sodium borohydride electrooxidation

Binary alloys of nickel (Ni) and dysprosium (Dy) or samarium (Sm) of different composition were prepared. Their electrocatalytic activity in respect to borohydride oxidation in alkaline medium was investigated by cyclic voltammetry, chronoamperometry and chronopotentiometry. It was correlated to their morphological and structural properties examined by SEM/EDXS and XRPD. Ni0.95Dy0.05 alloy electrode showed the highest electrocatalytic activity for BOR, and Ni0.90Sm0.10 showed the lowest. The activity of the rare earth alloys was compared to other Ni– and Pt–based materials, with promising results being reported, which envisage application of these materials as electrodes in direct borohydride fuel cells.

Carbon Supported Nanocrystalline Manganese Oxide: Surpassing Platinum as Oxygen Reduction Catalyst in Direct Borohydride Fuel Cells

Manganese oxide (MnO2) nanodispersed on high surface area carbon was tested as cathode catalyst for direct borohydride fuel cells with an anion conducting membrane. In order to investigate the effects of borohydride crossover, ex-situ experiments toward oxygen reduction reaction were conducted employing rotating disk electrodes in presence of borohydride and thiourea. Although platinum showed superior catalytic properties at ideal conditions, manganese oxide outperformed platinum significantly in presence of borohydride. Direct borohydride fuel cell tests were conducted using Pt/C-based and MnO2/C-based. After one hour of operation at 0.40 V the platinum based membrane electrode assembly lost approx. 30% of its initial peak power density while the non-precious metal MEA showed constant performance. The peak power density of the single test cell with a Pt/C based anode, an anion exchange membrane and a MnO2/C based cathode was 38 mW cm−2.

A Membrane-Free and Practical Mixed Electrolyte Direct Borohydride Fuel Cell

A membrane-free direct borohydride fuel cell that is operated with a borohydride containing electrolyte is designed and constructed. Main focus of this study is the cathode catalyst that has to show high tolerance against borohydride. Both catalysts, Ag-Mn3O4/C as cathode catalyst and commercial Pt/C as anode catalyst, are characterized electrochemically using a rotating disk electrode. The number of exchanged electrons is calculated employing Levich and Koutecky-Levich analysis. Cathodes are fabricated using a cross rolling method with an in-house made gas diffusion layer. A cell with an implemented Luggin capillary is designed in order to follow the electrode potentials. The BH4−/O2 fuel cell shows a power density of 17 mW cm−2 using a 1 M NaBH4/1 M NaOH/5 mM thiourea electrolyte.

Three-dimensional nanostructured Ni–Cu foams for borohydride oxidation

Three-dimensional (3D) nanostructured nickel–copper (Ni–Cu) foams have been prepared by electrodeposition using a dynamic hydrogen template. These 3D materials were tested as electrodes for the borohydride oxidation reaction (BOR) in alkaline media for possible application as anodes of direct borohydride fuel cells. Their activity in BOR was studied using cyclic voltammetry, chronoamperometry, and chronopotentiometry and main reaction parameters and electrodes’ stability were evaluated.

Performance study of passive and active direct borohydride fuel cell employing a commercial Pd decorated Ni–Co/C anode catalyst

In this study, a new Pd decorated Ni–Co/C anode catalyst with remarkably high performance was introduced for using in direct borohydride fuel cell (DBFC) and compared to conventional 10wt.% Pt/C anode catalyst. The activity and poisoning tolerance of both catalysts were investigated by electrochemical techniques in half-cell. The results indicated that the Pd decorated Ni–Co/C had higher activity compared to the 10wt.% Pt/C in borohydride oxidation reaction (BOR). However, its poisoning tolerance was lower than 10wt.% Pt/C during 200 cycles.Passive DBFC results demonstrated that the cell performance and open circuit voltage (OCV) were improved by using the Pd decorated Ni–Co/C as an anode catalyst compared to commercial 10wt.% Pt/C; 126mWcm−2 vs. 76mWcm−2 and 1010mV vs. 892mV respectively. Moreover, the maximum peak power density of 761mWcm−2 was obtained by Pd decorated Ni–Co/C anode catalyst in active DBFC which is comparable to generated power by H2/O2 proton exchange membrane fuel cell (PEMFC); 772mWcm−2 at the same conditions.

Carbon Supported Ruthenium as Anode Catalyst for Alkaline Direct Borohydride Fuel Cells

Electrochemical borohydride oxidation on nanodispersed ruthenium supported on high surface area carbon (Ru/C) is investigated by means of cyclic voltammetry, CO-stripping, rotating disk electrode experiments and chronoamperometry as well as direct borohydride fuel cell tests in a mixed electrolyte approach. All experimental results of Ru/C are compared to a commercially available Pt/C catalyst. Ru/C shows high Coulombic efficiency with a complete eight electron transfer at low anodic potentials. The electrochemical active potential window is −0.05–0.30 V vs RHE with higher activity compared to Pt/C in diffusion limited regions. In situ fuel cell tests show superior behavior in current density areas below 20 mA cm–2.

High electrocatalytic activity for borohydride oxidation on palladium nanocubes enclosed by {200} facets

Pd nanocubes enclosed by {200} facets are synthesized and used as an anode catalyst in direct borohydride fuel cell (DBFC) to study the electrocatalytic activity of Pd towards borohydride oxidation reaction (BOR) by modifying its surface atomic structure. A 7e reaction towards BOR is implemented on Pd nanocubes with a borohydride concentration as high as 3.26 M. The cell using Pd nanocubes as anode catalyst exhibits an obvious higher power density than the cell using commercial Pd/C, and maintained 99% of its voltage after 50 h stability test. It suggests that the Pd nanocubes could be a promising anode catalyst for the DBFC application.

Estimating the energy density of direct borohydride–hydrogen peroxide fuel cell systems for air-independent propulsion applications

The energy density of DBPFCs (direct borohydride–hydrogen peroxide fuel cells) is estimated for air-independent propulsion applications. The performance of DBPFCs containing heat-treated electrocatalysts supported on multiwalled carbon nanotubes is evaluated. The open circuit voltage and the maximum power density are 1.44 V and 243 mW/cm2, respectively, whereas the voltage efficiency is 17.9% at the maximum power density. Based on experimental results, the energy density is estimated to be 63.2 Wh/kg (87.1 Wh/L), which is much lower than those of other power sources. The degree of influence of various parameters on the energy density is ranked in the following order: fuel utilization efficiency > voltage efficiency > H2O2 (hydrogen peroxide) concentration > NaBH4 (sodium borohydride) concentration > maximum power density. Performance targets comprising of fuel utilization efficiency of 90%, voltage efficiency of 40%, H2O2 concentration of 50 wt%, NaBH4 concentration of 20 wt%, and maximum power density of 650 mW/cm2, have been determined. Under these conditions, the energy density and fuel volume are expected to be 378.5 Wh/kg (541.4 Wh/L) and 1.57 L, respectively, which would allow them to be used widely as power sources for air-independent propulsion.

Investigation of platinum and palladium as potential anodic catalysts for direct borohydride and ammonia borane fuel cells

Platinum and palladium are investigated as anodic catalysts for direct borohydride and direct ammonia borane fuel cells (DBFC and DABFC). Half-cell characterizations performed at 25 °C using NH3BH3 or NaBH4 alkaline electrolytes demonstrate the lowest open-circuit potential and highest electrocatalytic activity for the NH3BH3 alkaline electrolyte for Pd and Pt rotating disk electrodes, respectively. Voltammograms performed in fuel cell configuration at 25 °C confirm this trend: the highest open circuit voltage (1.05 V) and peak power density (181 mW·cm−2) are monitored for DABFC using Pd/C and Pt/C anodes, respectively. Increasing the temperature heightens the peak power density (that reaches 420 mW·cm−2 at 60 °C for DBFC using Pt/C anodes), but strongly generates gas from the fuel hydrolysis, hindering the overall fuel cells performances. The anode texture strongly influences the fuel cell performances, highlighting: (i) that an open anode texture is required to efficiently circulate the anolyte and (ii) the difficulty to compare potential anodic catalysts characterized using different fuel cell setups within the literature. Furthermore, TEM imaging of Pt/C and Pd/C catalysts prior/post DBFC and DABFC operation shows fast degradation of the carbon-supported nanoparticles.

Perovskite cathodes for NaBH4/H2O2 direct fuel cells

Perovskite-type oxides are evaluated as cathodes for hydrogen peroxide (H2O2) reduction in direct borohydride fuel cells (DBFCs). The study is conducted on button-type ceramic electrodes of LaCoO3 (LC), La0.84Sr0.16CoO3 (LSC), La0.8Sr0.2Fe0.8Co0.2O3 (LSFC), and La0.7Sr0.3MnO3 (LSM), thus avoiding cross-contributions of carbon or nickel catalyst supports. Cyclic voltammetry shows that LSM has the highest activity for H2O2 reduction in alkaline solution, with the other three materials showing minimal (LC) to none (LSC, LSFC) electroactivity. The data also suggest that only LC and LSM are stable within the tested potential window, although the alteration of the samples surface is apparent in scanning electron microscopy images collected after the electrochemical measurements. The analysis of LSM by chronopotentiometry in light of the Sand equation indicates ca. 1 electron involved in the H2O2 reduction. A demonstration DBFC employing a single phase LSM ceramic cathode yields a peak power density of 8.2mWcm−2 at 28mAcm−2, at 45°C. This value is about 60% of that obtained with a commercial platinum foil electrode, which is a notable feature and demonstrates the potential of LSM as an alternative low cost cathode for DBFCs.

Synthesis, Characterization and Properties of the Graphene Supported Pt-Co Nanocatalysts Towards the Electro-Oxidation of Methanol

Among the different types of fuel cell technologies, direct methanol fuel cells (DMFCs) are the most suitable for mobile and portable electronic applications. The development of cost-effective, active, and stable catalysts, able to substitute Pt or allow reducing the amount of it in low temperature fuel cell anodes is still in progress. In our previous works [1, 2] it has been shown that the graphene supported platinum-cobalt catalysts prepared by means of microwave synthesis enhance electrocatalytic activity towards the oxidation of borohydride and ethanol in an alkaline medium and are promising anode materials for direct borohydride fuel cells (DBFCs) and ethanol fuel cells (DEFCs). In this study investigation of activity of the graphene supported platinum-cobalt catalysts with the different Pt:Co molar ratios, fabricated by the rapid microwave heating method, towards the electro-oxidation of methanol in an acidic medium is presented. The Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60 were prepared by microwave-assisted heating of required amounts of Pt(IV), Co(II) and ethylene glycol at a temperature 170 oC for 30 min. For comparison, the graphene supported Pt catalyst was also prepared at 170 oC for 30 s. The Pt loading in the synthesized catalysts was near 0.1 mg Pt cm-2. The electrochemically active surface areas of Pt in the synthesized Pt/GR and Pt-Co/GR catalysts were determined from the cyclic voltammograms of the mentioned catalysts recorded in a deaerated 0.5 M H2SO4 solution at a sweep rate 50 mV s-1 by calculating the charge associated with hydrogen adsorption (220 µCcm-2) and are 0.7 cm2 for Pt/GR and 5.2, 2.9, 1.6, 1.0 and 0.5 cm2for the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20, 1:50 and 1:60, respectively. Values of the electrochemically active surface areas of the investigated Pt-Co/GR catalysts are 1.4-7.5 times higher than those of the Pt/GR catalyst. Electrochemical properties of Pt-Co/GR were investigated towards the electro-oxidation of methanol in acidic medium by means of cyclic voltammetry and chronoamperometry and compared with those of the bare graphene supported Pt catalyst. It has been determined that the Pt-Co/GR catalysts with the Pt:Co molar ratios equal to 1:3, 1:6, 1:20 exhibit an enhanced electrocatalytic performance for methanol electro-oxidation as compared with that of bare graphene supported platinum catalyst. Methanol oxidation current density values are ca. 2.1-3.2 times higher at the Pt-Co/GR catalysts with the above mention Pt:Co molar ratios than those at the Pt/GR catalyst. Highest electrocatalytic activity towards the electro-oxidation of methanol in acidic medium shows the graphene supported Pt-Co catalyst with the Pt:Co molar ratios equal to 1:3 and 1:6 as compared with that of catalysts with higher Pt:Co molar ratios and Pt/GR. These results obtained show that the Pt-Co/GR catalysts with the different Pt:Co molar ratios could have promising future as catalysts for DMFC.

Borohydride Electro-Oxidation on Ni-Based Electrocatalysts: Investigation of Electrocatalytic Activity and Hydrolysis Process

Direct borohydride fuel cells (DBFCs) or borohydride batteries are promising devices since they present high energy density and involve easy handling and storage of the fuel (1). Sodium borohydride can be used directly or dissolved in an alkaline electrolyte (2), which enable the use of non-noble metals as catalysts. However, the development of such devices is hampered by the low efficiency BH4 - electro-oxidation, because of the parallel occurrence of BH4 - hydrolysis, leading to borates and hydrogen evolution (3). Therefore, the development of electrocatalysts that allow minimization of the hydrogen release is of paramount importance for improving the viability of such electrochemical systems. In this context, this work aims at investigating the electrocatalytic activity and the extent of BH4 - hydrolysis at different nickel-based materials (Ni powder, NiO/C and LaNi4.7Sn0.2Cu0.1). The NiO/C catalysts were prepared by a thermal decomposition method (4, 5) with 33 wt.% and 66 wt.% of metal on Vulcan carbon (XC-72R). The metal hydride alloy was prepared from high-purity metals by the arc melting technique under an inert gas atmosphere. The electrochemical cell used was jacketed to control de reaction temperature at 25°C. The working electrode was prepared depositing 10 mg of an ink composed by 50 mg of catalyst, 50 mg of carbon, 0.984 mL of water, 0.200 mL of iso-propanol and 0.516 mL of Nafion (5 – 10 % of water), on carbon paper (Toray). To improve the overall conductivity and the catalyst adhesion, the composites were hot-pressed for 5 min at 5 bar and 125oC. An Hg/HgO electrode was used as a reference electrode and Au wire served as counter electrode. Before and after the electrochemical tests, the electrocatalysts were characterized by XRD, XPS and TEM. Cyclic voltammetry (CVs) was performed in 1 M NaOH electrolyte in the absence and in the presence of 0.5 M sodium borohydride. Differential electrochemical mass spectrometry (DEMS) has been employed to evaluate the hydrogen formation during the borohydride oxidation. CV results with the electrocatalysts composed by nickel powder and carbon-supported nickel nanoparticles have shown high BH4 - oxidation currents, with an onset potential located at ca. -0,4V vs Hg/HgO. Chronoamperometric results presented a stable current profile. Furthermore, the results have shown that the exposition of the electrode to 0.5 M borohydride solution leads to significant hydrolysis. Interesting, for pure nickel particles (nickel powder), the hydrogen release resulting from BH4 - hydrolysis ceased after 3 hours, when the electrode was polarized above the BOR on set potential. On the other hand, the results for LaNi4.7Sn0.2Cu0.1 have shown that the hydrogen release initiates only after several hours of BH4 - oxidation, but it suffered deactivation during prolonged polarization measurements. These results for the pure Ni catalysts evidence that the surface phase produced during the BOR, becomes inactive for the BH4 - hydrolysis, but remained active for the BOR. This would increase the overall faradaic efficiency. For the alloyed material, the occurrence of a segregation phenomenon of the Ni atoms to the surface may initiate the catalysis of the hydrolysis process.

Electrochemical Oxidation of Borohydride for Direct Fuel Cells

The direct borohydride fuel cell (DBFC) is gaining more and more interest in recent years because of high energy density and the easy handling of liquid fuels. The oxidation of the borohydride anions at the anode delivers up to eight electrons per molecule at a theoretical potential of -1.24 V vs. SHE [1,2]: BH4 - + 8OH- → BO2 - + 6H2O + 8e- In combination with an oxygen cathode and an alkaline membrane or electrolyte an electrochemical cell with a nominal voltage of 1.64 V is formed. The electrochemical oxidation is investigated on various noble metal catalysts such as Pt/C, Au/C and Pd/C and bimetallic alloys thereof with first row transition metals. The electrochemical properties of the catalysts are characterized by cyclic voltammetry in alkaline electrolyte containing NaBH4 in standard three electrode configuration with a rotating disc electrode (RDE) [3]. Figure 1 : Cyclic voltammograms of Pt/C with 5mM NaBH4 on a RDE, anodic sweeps at 200, 400, 600, 900, 1200, 1600 and 2000 rpm. The borohydride oxidation on Pt/C starts at around -50 mV vs. RHE getting diffusion limited at 200 mV vs. RHE with a complete eight electron transfer. Due to diffusion limitation data processing according to Levich and Koutecky-Levich is possible. Figure 2 : Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1) Figure 3 : Koutecky-Levich plot of Pt/C catalyst at 0.50 V vs. RHE (data from Fig. 1) Levich and Koutecky-Levich (Fig. 2 and 3) analysis show an eight electron transfer reaction at a potential of 0.5 V vs. RHE in the diffusion controlled region and as well at 0.01 V vs. RHE in the kinetic controlled region. Although platinum shows excellent catalytic activity towards borohydride electrooxidation, the main side reaction, namely the hydrolysis reaction is also catalyzed. Besides the loss of fuel, the formation of gaseous hydrogen can harm the electrode due to mechanical stress. This issue can be addressed by replacing platinum with less active catalysts. Gold based electrocatalysts for example do not catalyze the hydrolysis side reaction. On the roadway towards a practicable application it is necessary to improve the selectivity at the anode catalyst system. Acknowledgements Support by NAWI Graz and financial support by the Austrian Federal Ministry of Transport, Innovation and Technology (BMVIT) and The Austrian Research Promotion Agency (FFG) through the program a3plus and the IEA research cooperation is gratefully acknowledged.

Anodic behavior of carbon supported Cu@Ag core–shell nanocatalysts in direct borohydride fuel cells

Carbon-supported Cu@Ag core–shell nanoparticles are prepared by a successive reduction method in an aqueous solution and are used as an anode electrocatalyst for the direct borohydride–hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties of the as-prepared electrocatalysts are investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronopotentiometry (CP), and fuel cell tests. In situ Fourier transform infrared (FTIR) spectroscopy is employed in 2 M NaOH/0.1 M NaBH4 to understand the borohydride oxidation reaction (BOR) mechanism by studying the intermediate reactions occurring on the Cu@Ag/C electrode. The TEM images show that the average size of the Cu1@Ag1/C particles is approximately 18 nm. Among the as-prepared catalysts, the Cu2@Ag1/C catalyst presents the highest catalytic activity. As shown by in situ FTIR, the oxidation reaction mechanism of BH4− is similar to that of Ag/C: BHn(OH)4−n−+2OH−→BHn−1(OH)5−n−+H2O+2e. At 25 °C, the DBHFC with Cu2@Ag1/C as the anode electrocatalyst and Pt mesh (1 cm2) as the cathode electrode exhibits a maximum anodic power density of 17.27 mW mg−1 at a discharge current density of 27.8 mA mg−1.