Performance Of Direct Borohydride Fuel Cell Research Articles

Direct borohydride fuel cells: A selected review of their reaction mechanisms, electrocatalysts, and influence of operating parameters on their performance

Direct borohydride fuel cells (DBFC) oxidize an easily-stored energy-dense borohydride fuel (sodium borohydride: NaBH 4 ), that in theory reacts ca . 400 mV below H 2 and produces 8 electrons per BH 4 - anion. However, the borohydride oxidation reaction (BOR) does not fully meet these promises in practice: the electrocatalyst nature, structure and state-of-surface, and the operating conditions (pH, BH 4 - concentration, temperature, fluxes) noticeably influence the BOR kinetics and mechanism. Nickel and platinum-based catalysts both have assets for the BOR. DBFCs can only yield decent performance if their separator combines high ion-conductivity and efficient separation of the reactants; cation-exchange membranes, anion-exchange membranes, bipolar membranes and porous separators all have their own advantages and drawbacks. Besides the anode, the choice of separator must consider the DBFC cathode reaction, where oxygen (usually from air) or hydrogen peroxide are reduced, provided adapted catalysts are used. All these aspects drive the DBFC performance and stability/durability. • The BOR kinetics/mechanism strongly depends on the catalyst and operating parameters. • Metallic nickel is highly efficient at low potential values but leads to high H 2 escape. • Platinum leads to fast kinetics of the H 2 production from BH 4 - and fast H 2 oxidation. • Depending on the membrane/separator, DBFC must employ BH 4 - tolerant cathodes. • The morphology of the electrode, diffusion medium and bipolar plate channels impact mass-transport hence DBFC performance.

Investigation of the performance of a direct borohydride fuel cell with low Pt/C catalyst loading under different operating conditions

Fuel cells are promising alternative energy converters in terms of preventing pollution, efficiency, and noise. Direct borohydride fuel cells (DBFCs) which are defined as a sub-class of polymer electrolyte membrane fuel cells (PEMFCs) and direct liquid fuel cells (DLFC) have increased attention recently since they offer a solution for hydrogen storage problem. However, the commercialization of DBFC is hindered by the need of high platinum loadings. Therefore, reducing the platinum content is crucial to develop cost-effective DBFC without compromising performance. This research focuses on the effects of operational parameters on the DBFC performance with low level Pt/C catalyst loading (anode: 0.32 mg/cm2, cathode: 0.36 mg/cm2). The gas diffusion electrode was prepared by spray-coating technique. The peak power density of 19.95 mW/cm2 was obtained at 80 °C when 1 mL/min was used as a flow rate of fuel.

A highly stable Cu(OH)2-Poly(vinyl alcohol) nanocomposite membrane for dramatically enhanced direct borohydride fuel cell performance

Nano-additive aggregation, limited performance, and unclear modification mechanisms are the main obstacles in developing nanocomposite anion exchange membranes (AEMs). In this work, for the first time, an effective and highly stable Poly(vinyl alcohol) (PVA)-based AEMs with dispersive Cu(OH)2 nanoclusters (Cu-AEMs) are prepared by a simple and eco-friendly three-step method: ‘CuCl2 doping-casting-KOH immersing’. The doped Cu2+ ions chemically combine with OH− ions to form anionic conductive Cu(OH)2 nanoclusters intermediated by attaching resins. The PVA skeletons wrap around Cu(OH)2 while the hydroxyl groups expose to bulk water, forming Cu(OH)2-PVA complex, which avoids nano-additive aggregation, increases anionic channels, and strengthens additive-matrix connection. A direct borohydride fuel cell using Cu-AEM with 0.56 wt % CuCl2 possess the highest power density of 403.3 mW cm−2 at 60 °C and a life span of over 200 h. The high-performance and durability come from the unique structure of Cu(OH)2 nanoclusters-PVA complex. ‘Vehicle’ theory is considered to be the dominant mechanism for enhancing such nanocomposite Cu-AEMs. This work demonstrates a new concept for preparing the stable AEMs toward high-performance fuel cells. The synthetic chemistry involved can be broadly extended for fabricating versatile AEMs.

A Development in Direct Borohydride/Hydrogen Peroxide Fuel Cell Using Nanostructured Ni‐Pt/C Anode

AbstractA direct borohydride fuel cell (DBFC) using H2O2 as oxidizer has been developed. The NaBH4/H2O2 fuel cell is assembled by using Ni‐Pt/C composite as anode catalyst, Pt/C as cathode catalyst, and Nafion® membrane as electrolyte. The compositions, morphology and particle sizes and of catalysts are evaluated by means of scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), scanning electron microscopy and transmission electron microscopy (TEM), respectively. TEM images show that Ni‐Pt/C nanoparticles have an even size distribution with an average diameter of less than 20 nm. In this work, DBFC performance is studied under different operation conditions including operation temperature, borohydride concentration, and oxidant concentration. The experimental results show that the power density increased by increasing the temperature and increasing the concentration of oxidant. Experiments also show that electrochemical performance is not considerably affected by NaBH4 concentration. So that, it is found that 1.5M NaBH4 concentration is optimum for DBFC operation. A maximum power density of 140 mW cm−2 or 0.11 mW µg−1Pt total has been achieved at a cell voltage of 1.011 V at 55 °C. The cell is operated for about 72 h and its performance stability is recorded.

Evaluation of operating conditions on DBFC (direct borohydride fuel cell) performance with PtRu anode catalyst by response surface method

Borohydride has been considered as a potential fuel for the fuel cell application due to its high energy density. A DBFC (direct borohydride fuel cell) is an electrochemical device that converts chemical energy stored in borohydride and oxidant directly to electrical energy as long as the fuel and oxidant is supplied. One of the main problems encountered in a DBFC is the simultaneous hydrolysis of BH4− at the anode surface. The hydrolysis decreases the fuel utilization and fuel cell performance, since hydrogen bubbles hinder the contact of catalyst with reactant. This study investigates the effect of operating conditions (cell temperature, borohydride concentration, flow rates of fuel and oxidant) on DBFC performance by RSM (response surface methodology). PtRu/C is used as the anode catalyst to systematically investigate the effect of hydrogen evolution rate on the fuel cell performance. The maximum power density is obtained at 80 °C fuel cell temperature, 0.5 M NaBH4 concentration, 5 cm3 min−1 flow of anolyte and 100 cm3 min−1 flow of oxygen.

Performance degradation of a direct borohydride fuel cell

This study explores the performance degradation mechanism of direct borohydride fuel cells (DBFCs) by investigating the catalyst surface characteristics, electrode structure, and electrode polarization after cell operation. Catalyst erosion from the anode substrate is a major cause of DBFC performance degradation. The depression of hydrogen evolution effectively stabilizes DBFC performance. DBFCs using Ni–Pd/C as the anode catalyst and polypyrrole-modified carbon-supported Co(OH)2 [Co(OH)2–PPy/BP] as the cathode catalyst exhibit high performance stability. The performance stability of Co(OH)2–PPy/BP is similar to that of commercial Pt/C, although only a small amount of Co remains after operation. The cooperative interaction among Co, N from polypyrrole, and C from the carbon supporter plays a very important role in the performance stability of a DBFC cathode.

Direct borohydride fuel cell performance using hydroxide‐conducting polymeric nanocomposite electrolytes

Solid electrolyte membranes based on alkali‐doped polyvinyl alcohol (PVA) and PVA/carbon nanotubes (PVA/CNTs) are used in direct borohydride fuel cells (DBFCs). As 0.05 wt % of CNT is incorporated into the PVA matrix, the polymer crystallinity is decreased from 42.4% to 38.0% and the fractional free volume increases from 2.48% to 3.53%. The KOH‐doped PVA/CNT exhibits the highest ionic conductivity of 0.0805 S cm−1, because of the increased polymer free volume (which promotes vehicular OH− transport) and the presence of CNT (which serves as the conducting microchannels). Sodium borohydride (NaBH4) in NaOH solution and potassium borohydride (KBH4) in KOH mixture are fed into the cells. The power density of the KBH4‐based DBFC is almost twice that of the NaBH4‐based DBFC (184 vs. 92 mW cm−2) due to less KBH4 permeability through the films, higher conductivity of the KOH‐doped PVA composites than those in the sodium counterpart, and probably higher electro‐catalytic kinetics. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1779–1789, 2013

Anion- or Cation-Exchange Membranes for NaBH4/H2O2 Fuel Cells?

Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC’s performance. Cell polarization, power density, stability, and durability tests are used in the membranes’ evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load.

Effect of Membrane Separators on the Performance of Direct Borohydride Fuel Cells

The effect of the separator type on the performance of laboratory direct borohydride fuel cells (DBFCs) using hydrogen peroxide as the oxidant, is studied at room temperature. Five commercial ion exchange membranes from Nafion (N117, 115CS, NRE-212) and IONAC (MC-3470, MA-3475) brands are considered as separators for the DBFC. The membranes are directly compared by the observation and analysis of the corresponding DBFC's performance. Cell polarization, power density, stability, and durability tests are used for the evaluation. Energy densities and specific capacities estimated for a 2-hour cell operation at 0.6 V are up to 45 Wh kg−1 and 76 Ah kg−1, respectively, when using a Nafion NRE-212 membrane separator. A peak power density of 96 mW cm−2, at 0.6 V and 160 mA cm−2, is reported for the DBFC using Nafion N117, but these values cannot be sustained for appreciable operation times. For long term cell operation the IONAC MC-3470 membrane seems to outperform the stability of the benchmark Nafion membranes. The IONAC membranes’ lower cost is a good motivation but further optimization is required to improve their instantaneous power load.

Improving the direct borohydride fuel cell performance with thiourea as the additive in the sodium borohydride solution

In this study, the effects of the additive thiourea (TU) have been investigated under steady state/steady-flow and uniform state/uniform-flow systems with the aim of minimizing the anodic hydrogen evolution on Pd in order to increase the performance of a direct borohydride fuel cell. The fuel cell has consisted of Pd/C anode, Pt/C cathode and Na + form Nafion membrane as the electrolyte. There has been a small improvement in peak power density and fuel utilization ratio by addition of TU (1.6 × 10 −3 M) into the sodium borohydride solution; the peak power densities of 14.4 and 15.1 mW cm −2, and fuel utilization ratios of 21.6% and 23.2% have been obtained without and with TU, respectively.

Direct borohydride fuel cell using Ni-based composite anodes

In this study, nickel-based composite anode catalysts consisting of Ni with either Pd on carbon or Pt on carbon (the ratio of Ni:Pd or Ni:Pt being 25:1) were prepared for use in direct borohydride fuel cells (DBFCs). Cathode catalysts used were 1 mg cm −2 Pt/C or Pd electrodeposited on activated carbon cloth. The oxidants were oxygen, oxygen in air, or acidified hydrogen peroxide. Alkaline solution of sodium borohydride was used as fuel in the cell. High power performance has been achieved by DBFC using non-precious metal, Ni-based composite anodes with relatively low anodic loading (e.g., 270 mW cm −2 for NaBH 4/O 2 fuel cell at 60 °C, 665 mW cm −2 for NaBH 4/H 2O 2 fuel cell at 60 °C). Effects of temperature, oxidant, and anode catalyst loading on the DBFC performance were investigated. The cell was operated for about 100 h and its performance stability was recorded.

Influence of operation conditions on direct NaBH 4/H 2O 2 fuel cell performance

Although hydrogen fuel cells have attracted so much attentions in these years because of the application prospect in electric vehicles, some obstacles have not been solved yet, among which hydrogen storage is one of the biggest. Direct borohydride fuel cell (DBFC) is another choice without hydrogen storage problem because borohydride is used as reactant directly in the fuel cell. In this paper, DBFC performance under different operation conditions was studied including electrolyte membrane type, operation temperature, borohydride concentration, supporting electrolyte and oxidant. Results showed that, with Pt/C and MnO 2 as anode and cathode electrocatalyst, respectively, Nafion ® 117 membrane as electrolyte, 1.0 M, 3.0 M and 6.0 M NaBH 4 and H 2O 2 solution in NaOH as reactant solution, 80 °C operation, the peak power density could reach 130 mW/cm 2.

Effects of operation conditions on direct borohydride fuel cell performance

In this study, the influences of different operational conditions such as cell temperature, sodium hydroxide concentration, oxidant conditions and catalyst loading on the performance of direct borohydride fuel cell which consisted of Pd/C anode, Pt/C cathode and Na + form Nafion membrane as the electrolyte were investigated. The experimental results showed that the power density increased by increasing the temperature and increasing the flow rate of oxidant. Furthermore, it was found that 20 wt.% of NaOH concentration was optimum for DBFC operation. When oxygen was used as oxidant instead of air, better performance was observed. Experiments also showed that electrochemical performance was not considerably affected by humidification levels. An enhanced power density was found by increasing the loading of anodic catalyst. In the present study, a maximum power density of 27.6 mW cm −2 at a cell voltage of 0.85 V was achieved at 55 mA cm −2 at 60 °C when humidified air was used.

Depression of hydrogen evolution during operation of a direct borohydride fuel cell

Hydrogen evolution from the anode usually occurs during operation of a Direct Borohydride Fuel Cell (DBFC). This would not only decrease the fuel utilization, but also lower the cell performance because hydrogen bubbles would hinder ion movement in the anolyte. In this paper, the hydrogen evolution behavior is investigated based on relations of hydrogen evolution rates versus operation currents of the DBFC. The effects of anode modification on the hydrogen evolution rate and the cell performance were investigated. It was found that hydrogen evolution was depressed by adding Pd, Ag and Au catalysts in the anode. Coating a thin Nafion film on the catalyst surfaces was another effective way to decrease the hydrogen evolution rate. Depression of the hydrogen evolution and improvement of the DBFC performance can be achieved by adding carbon supported Pd in Ni anode with a suitable content of Nafion. However, too much Nafion in the anode would degrade the DBFC performance.

Material Aspects of the Design and Operation of Direct Borohydride Fuel Cells

AbstractThe direct borohydride fuel cell (DBFC) has attracted increasing interest as a potential high power source for mobile and portable applications. Engineering design plays an important role in the development of the DBFC. This paper reports data for the selection of anode, cathode, and membrane materials for the DBFC. The best DBFC performance is achieved with a Au anode, a Pt cathode, and a 3541P ion exchange membrane. The use of non‐precious catalysts, e.g., Ag, leads to promising results.

Influence of operation conditions on direct borohydride fuel cell performance

The effects of temperature, concentration of borohydride and supporting electrolyte and oxidant conditions on the performance of direct borohydride fuel cell are reported. Design of flow fields and evaluation of effects of flow conditions were carried out. Durability of the DBFCs was tested over a relatively long period.