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The homogeneous/heterogeneous catalyst combination of VO2+ in anolyte with Pd/C at the anode is first introduced in a formic acid fuel cell to enhance HCOOH electrooxidation. The VO2+/Pd catalyst combination establishes a stepwise reaction pathway involving HCOOH dehydrogenation to form V3+ from VO2+ reduction and subsequent V3+ electrooxidation to regain VO2+. The fuel cell with the VO2+/Pd combination presents a peak power density of 341.3 mW cm−2 and stable power density higher than 30 mW cm−2. [ABSTRACT FROM AUTHOR]

In this study, we synthesized ZrO 2 nanorods through a hydrothermal process as a catalyst precursor for the reversible hydrogen storage reaction between 2LiH + MgB 2 and 2LiBH 4 + MgH 2. The 2LiH + MgB 2 composites doped with the ZrO 2 nanorods demonstrated superior and stable hydriding/dehydriding kinetics upon cycling. The XRD, SEM and HRTEM results revealed that the doped ZrO 2 nanorods were transformed into ZrB 2 nanoparticles with a size of a few nanometers during the first hydrogenation. The initial nanosize of the ZrO 2 catalyst precursor accounted for the formation of extremely fine ZrB 2 nanoparticles, which acted as heterogeneous nuclei of MgB 2 . The present study provides a new route for performance enhancement of complex hydride composites through manipulating the nanostructure of catalysts. [ABSTRACT FROM AUTHOR]

A series of cobalt-doped catalysts (Co–PPy/BP) is synthesized by hydrothermal treatment of polypyrrole-modified BP2000 in cobalt nitride solution. The hydrothermal temperature is varied from 80 °C to 180 °C to investigate the effect of treatment temperature on the catalytic site formation for oxygen reduction reaction (ORR). Treatment temperature is found to slightly affect the structure and morphology of the synthesized catalysts. However, the catalytic activity of the synthesized Co–PPy/BP increases with increased treatment temperature up to 160 °C because higher treatment temperatures promote pyrrolic-N conversion to Co–Nx. Co–Nx catalyzes H2O2 electroreduction reaction, which increases the number of electrons transferred during ORR. However, the hydrothermal treatment at 180 °C leads to decreased pyrrolic-N and Co–Nx contents, which results in decreased catalytic activity of the synthesized Co–PPy/BP. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study was performed on four LiBH4-based hydrogen storage composites 2LiBH4 + MgX2 and 6LiBH4 + CaX2 (X = H and F). The composites with fluorides and those with corresponding hydrides exhibited similar hydrogen storage properties. The dehydrogenation of 2LiBH4 + MgF2 demonstrated a strong dependence on the hydrogen back pressure, similar to that of 2LiBH4 + MgH2. The reversible hydrogen storage of 2LiBH4 + MgF2 was achieved under a back pressure of 5 bar at 450 °C. Dehydrogenation under lower H2 pressures resulted in the production of Mg and thus a partial reversibility. In contrast, both 6LiBH4 + CaH2 and 6LiBH4 + CaF2 revealed reversible hydrogen storage properties regardless of the hydrogen back pressure. The structural difference between MgB2 and CaB6 may account for the observed differences in hydrogen storage properties of the Mg- and Ca-containing LiBH4 reactive composites. [Copyright &y& Elsevier]

Abstract: LiBH4+1/2MgH2 is a promising reactive hydride composite for hydrogen storage. In the present study, three Ce-based additives were used as catalysts to enhance the hydrogen storage performance of LiBH4+1/2MgH2 composites. The composites with Ce additives demonstrated significantly improved dehydrogenation kinetics and cyclic stability compared with the pure composite. X-ray diffraction and scanning electron microscopy analyses clearly revealed the phase transitions and morphological evolution during the hydriding-dehydriding cycling. The composites with Ce-based additives displayed stable nanostructures, in contrast to the rapid microstructural deterioration in the uncatalyzed composite. The CeB6 formed in the composites had a particle size of 10 nm after five cycles. It may act as the nucleus for MgB2 formation during dehydrogenation and thus account for the structural and performance stability of the composites upon cycling. [Copyright &y& Elsevier]

Abstract: The dehydrogenation temperature of LiBH4 was considerably decreased to 230 °C–300 °C when it was manually mixed with FeCl2, CoCl2 and NiCl2 in a molar ratio of 2:1. Mixing LiBH4 with NiCl2 or FeCl2 led to complete hydrogen desorption from LiBH4, i.e. 18.3 wt% hydrogen was achieved with respect to the weight of LiBH4. However, the CoCl2 addition resulted in less hydrogen release due to the formation of diborane. Ball milling treatment for the mixtures of LiBH4 and these chlorides further decreased hydrogen desorption temperatures. The results indicate that LiBH4 could be effectively destabilized by the chlorides of Fe, Co and Ni. Small doping of these chlorides into LiBH4 was found to be effective in enhancing dehydrogenation kinetics of the remaining LiBH4 due to the formation of metal borides. [Copyright &y& Elsevier]

Abstract: The fuel efficiency of borohydride electro-oxidation on carbon-supported Au and Ag electrodes was found to be highly dependent on the concentration ratio of [OH−]/[BH4 −] in the solution. Near-8e reactions occurred when [OH−]/[BH4 −]≥5. However when [OH−]/[BH4 −] was smaller than 5, hydrogen gas was evolved and the fuel efficiency was reduced. Only 3e reaction stoichiometry was obtained at [OH−]/[BH4 −]=1. Detailed cyclic voltammetry (CV) studies revealed that both the Au/C and Ag/C showed different anodic waves in varied NaOH–NaBH4 solutions. The CV analysis results suggest that BH3OH−, an intermediate possibly produced by homogeneous hydrolysis, is responsible for the electrochemical reaction at [OH−]/[BH4 −]=1. Comparison of CV voltammograms in borohydride solutions with that in the H2-bubbled NaOH solution suggests that borohydride electro-oxidation on Au or Ag electrode is through direct BH4 − oxidation rather than through a hydrogen ionization mechanism. It is concluded that there exists an inherent competition between two oxidizing species of OH− and H2O during borohydride electro-oxidation, that is, if accessible OH− ions are not sufficient for each BH4 − to accomplish the 8e electro-oxidation, part of BH4 − will react simultaneously with H2O to generate hydrogen. [Copyright &y& Elsevier]

Abstract: In the present work, a Pd catalyst supported on multiwalled carbon nanotubes (MWCNTs) is successfully synthesized and its property as the anode material for borohydride oxidation is investigated. Compared with other carbon-supported Pd catalysts, the Pd/MWCNT catalyst exhibits improved polarization properties due to its smaller Pd particles dispersing homogeneously on carbon nanotubes. The hydrogen evolution behavior on the Pd/activated carbon sample is found to be very sensitive to the concentrations of NaOH and NaBH4 in the solution. On the other hand, borohydride oxidation on Pd/carbon black and Pd/MWCNT displays reaction mechanisms near the 4e stoichiometry. It is thus supposed that the primary direct borohydride oxidation on Pd may be a 4e reaction. The simultaneous electro-oxidation of adsorbed hydrogen occurs conditionally, depending on its relative activity with the direct oxidation of BH4 −. [Copyright &y& Elsevier]

Abstract: Co-B catalysts were prepared by the chemical reduction of CoCl2 with NaBH4 for hydrogen generation from borohydride hydrolysis. The catalytic properties of the Co-B catalysts were found to be sensitive to the preparation conditions including pH of the NaBH4 solution and mixing manner of the precursors. A Co-B catalyst with a very high catalytic activity was obtained through the formation of a colloidal Co(OH)2 intermediate. The ultra-fine particle size of 10nm accounted for its super activity for hydrogen generation with a maximum rate of 26Lmin−1 g−1 at 30°C. The catalyst also changed the hydrolysis kinetics from zero-order to first-order. [Copyright &y& Elsevier]

Abstract: The performance stability of the direct borohydride fuel cell (DBFC) working under passive conditions was studied in this work. The stability within hours was found to be greatly affected by mass transport properties of different cell components. It was significantly improved by modifying electrode structures, increasing hydrophobicity of the cathode and using pretreated membranes. On the other hand, the stability of the DBFC cell for more than 100h was determined by the durabilities of these cell components. The nickel anode and silver cathode were found to degrade after prolonged operations and thus the durabilities of these non-noble metal catalysts need to be improved. [Copyright &y& Elsevier]

Abstract: Direct borohydride fuel cell (DBFC) as a liquid type fuel cell is promising for portable applications. In this study, we report our recent progress in the micro-fuel cell development. A power density of 80mWcm−2 was achieved in passive mode at ambient conditions when using the anode containing nickel, carbon-supported Pd catalyst and Nafion ionomer. Current efficiency was also found to be greatly increased due to the use of Nafion rather than polytetrafluoroethylene (PTFE). Based on improvements on single cell performance, planar multi-cell power modules were assembled to study the feasibility of making high-performance and practical DBFC power units. A power of 2.5W was achieved in a fully passive eight-cell module after significantly simplifying cell structure. [Copyright &y& Elsevier]

Abstract: Influences of borohydride crossover on cathode performance were studied in a micro direct borohydride fuel cell (DBFC). The results showed that fuel crossover resulted in decreases in open circuit potentials of cathodes. On the other hand, effects of fuel crossover on cathode overpotentials strongly depended on the cathode material. The Pt/C cathode demonstrated a small potential drop of 0.11V, while the Ag/C cathode had a much larger potential drop of 0.26V under the same condition. Fuel crossover was found to be depressed during current operations. It is possible that fuel depletion happened around the anode during operation, resulting in a decrease of fuel concentration gradient across the membrane and thus less crossover. Experiments also showed that a balance in wet-proof property is essential for the cathode in the direct borohydride fuel cell and the stability of cell performance was mainly dependent on wet-proof durability of the cathode. [Copyright &y& Elsevier]