Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH₄ concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.     

Accurately measuring the hydrogen generation rate for hydrolysis of sodium borohydride on multiwalled carbon nanotubes/Co–B catalysts

Multiwalled carbon nanotubes supported cobalt–boron catalysts (Co–B/MWCNT) were developed via the chemical reduction of aqueous sodium borohydride with cobalt chloride for catalytic hydrolysis of alkaline NaBH₄ solution. The hydrogen generation (HG) rates were measured on an improved high-accuracy, low-cost and automatic HG rate measurement system based on the use of an electronic balance with high accuracy. The HG of Co–B/MWCNT catalyst was investigated as a function of heat treatment, solution temperature, Co–B loading and supporting materials. The catalyst was mesoporous structured and showed lower activation energy of 40.40 kJ mol⁻¹ for the hydrolysis of NaBH₄. The Co–B/MWCNT catalyst was not only highly active to achieve the average HG rate of 5.1 l min⁻¹ g⁻¹ compared to 3.1 l min⁻¹ g⁻¹ on Co–B/C catalyst under the same conditions but also reasonably stable for the continuous hydrolysis of NaBH₄ solution.     

A direct borohydride–peroxide fuel cell–LiPO battery hybrid motorcycle prototype – II

In this study, a direct borohydride–peroxide fuel cell (DBPFC)–LiPo battery hybrid motorcycle, called HYBROTO, was developed. The hybrid system was designed using a 10-cell DBPFC stack with 120 W of maximum power as the main power source, a 12 LiPo battery pack with 6300 mAh and 65 C for energy storage and as auxiliary power source, and a brushless DC (BLDC) motor. In addition, a voltage-monitoring integrated circuit for fuel cells, a battery management unit, and a motor control circuit were developed to command the DBPFC, LiPo battery, and BLDC motor, respectively. The hybrid system was managed and synchronized by a main control unit (MCU) containing a synchronous bidirectional buck–boost converter and a boost converter. For performance tests, the DBPFC–battery system and BLDC motor were installed in an electric motorcycle body. Performance tests were carried out in the hybrid system under a constant load of 60 W. The hybrid system showed a satisfactory performance under the constant load with an efficiency of 67%. However, the MCU requires further improvement to provide more stable power output. The motorcycle prototype was tested at the 2016 International Symposium on Sustainable Aviation organized by the Sustainable Aviation Research Society.     

Electrodeposition of Pt–Ru and Pt–Ru–Ni nanoclusters on multi-walled carbon nanotubes for direct methanol fuel cell

A full-electrochemical method is developed to deposit three dimension structure (3D) flowerlike platinum-ruthenium (PtRu) and platinum-ruthenium-nickel (PtRuNi) alloy nanoparticle clusters on multi-walled carbon nanotubes (MWCNTs) through a three-step process. The structure and elemental composition of the PtRu/MWCNTs and PtRuNi/MWCNTs catalysts are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray polycrystalline diffraction (XRD), IRIS advantage inductively coupled plasma atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The presence of Pt(0), Ru(0), Ni(0), Ni(OH)₂, NiOOH, RuO₂ and NiO is deduced from XPS data. Electrocatalytic properties of the resulting PtRu/MWCNTs and PtRuNi/MWCNTs nanocomposites for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) are investigated. Compared with the Pt/MWCNTs, PtNi/MWCNTs and PtRu/MWCNTs electrodes, an enhanced electrocatalytic activity and an appreciably improved resistance to CO poisoning are observed for the PtRuNi/MWCNTs electrode, which are attributed to the synergetic effect of bifunctional catalysis, three dimension structure, and oxygen functional groups which generated after electrochemical activation treatment on MWCNTs surface. The effect of electrodeposition conditions for the metal complexes on the composition and performance of the alloy nanoparticle clusters is also investigated. The optimized ratios for PtRu and PtRuNi alloy nanoparticle clusters are 8:2 and 8:1:1, respectively, in this experiment condition. The PtRuNi catalyst thus prepared exhibits excellent performance in the direct methanol fuel cells (DMFCs). The enhanced activity of the catalyst is surely throwing some light on the research and development of effective DMFCs catalysts.     

Bipolar polymer electrolyte interfaces for hydrogen–oxygen and direct borohydride fuel cells

Direct borohydride fuel cells (DBFCs) using liquid hydrogen peroxide as the oxidant are safe and attractive low temperature power sources for unmanned underwater vehicles (UUVs) as they have excellent energy and power density and do not feature compressed gases or a flammable fuel stream. One challenge to this system is the disparate pH environment between the anolyte fuel and catholyte oxidant streams. Herein, a bipolar interface membrane electrode assembly (BIMEA) is demonstrated for maintaining pH control of the anolyte and catholyte compartments of the fuel cell. The prepared DBFC with the BIMEA yielded a promising peak power density of 110 mW cm⁻². This study also investigated the same BIMEA for a hydrogen–oxygen fuel cell (H₂–O₂ FC). The type of gas diffusion layer used and the gas feed relative humidity were found to impact fuel cell performance. Finally, a BIMEA featuring a silver electrocatalyst at the cathode in a H₂–O₂ FC was successfully demonstrated.     

High electrocatalytic activity of cobalt–multiwalled carbon nanotubes–cosmetic cotton nanostructures for sodium borohydride electrooxidation

Flexible and wearable cobalt electrode with a unique three-dimensional hierarchical-network structure is prepared by electrodeposition of spherical Co particles onto multiwalled carbon nanotubes (MWNTs) which are assembled on the skeleton of cosmetic cotton (CC). The morphology and phase structure of the cobalt–multiwalled carbon nanotubes–cosmetic cotton (Co–MWNTs–CC) electrode are characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction spectrometer. The NaBH₄ electrooxidation performance on the Co–MWNTs–CC electrode is investigated by means of cyclic voltammetry and chronoamperometry. Results show that the Co–MWNTs–CC electrode exhibits remarkably high catalytic activity and good stability for NaBH₄ electrooxidation. The oxidation current density reaches as high as 170 mA cm⁻² at −0.7 V in 1.0 mol dm⁻³ NaOH and 0.1 mol dm⁻³ NaBH₄, which is higher than the most-related previous results.     

Polyoxometallate-stabilized Pt–Ru catalysts on multiwalled carbon nanotubes: Influence of preparation conditions on the performance of direct methanol fuel cells

A novel catalyst, polyoxometallate-stabilized platinum–ruthenium alloy nanoparticles supported on multiwalled carbon nanotubes (Pt–Ru–PMo₁₂-MWNTs), was synthesized by a microwave-assisted polyol process. The effects of microwave reaction time, microwave reaction power, and pH value of the reaction solution on the electrocatalytic properties of Pt–Ru–PMo₁₂-MWNTs catalysts were also investigated. The polyoxometallate (PMo₁₂) formed a self-assembled monolayer on the surface of the Pt/Ru nanoparticles and MWNTs, which effectively prevented the agglomeration of Pt, Ru nanoparticles and MWNTs, due to the electrostatic repulsive interactions between the negatively charged PMo₁₂ monolayers. Energy dispersive spectroscopy examination and electrochemical measurements showed that the loading content of Pt/Ru and their electrochemical activity vary with the synthesis conditions, such as pH, reaction time, and microwave power. It was found that the a Pt–Ru–PMo₁₂-MWNTs electrocatalyst with high Pt loading content, small crystallite size, and good electrocatalytic activity could be synthesized using a long reaction time, intermediate microwave power, and a pH value of 7. The electrocatalysts obtained were characterized using X-ray diffraction, and scanning and transmission electron microscopy. Their electrocatalytic properties were also investigated by using the cyclic voltammetry technique.     

Ni–Pt/C as anode electrocatalyst for a direct borohydride fuel cell

In this study, a series of Ni–Pt/C and Ni/C catalysts, which were employed as anode catalysts for a direct borohydride fuel cell (DBFC), were prepared and investigated by XRD, TEM, cyclic voltammetry, chronopotentiometry and fuel cell test. The particle size of Ni₃₇–Pt₃/C (mass ratio, Ni:Pt = 37:3) catalyst was sharply reduced by the addition of ultra low amount of Pt. And the electrochemical measurements showed that the electro-catalytic activity and stability of the Ni₃₇–Pt₃/C catalysts were improved compared with Ni/C catalyst. The DBFC employing Ni₃₇–Pt₃/C catalyst on the anode (metal loading, 1 mg cm⁻²) showed a maximum power density of 221.0 mW cm⁻² at 60 °C, while under identical condition the maximum power density was 150.6 mW cm⁻² for Ni/C. Furthermore, the polarization curves and hydrogen evolution behaviors on all the catalysts were investigated on the working conditions of the DBFC.     

Performance of supported Au–Co alloy as the anode catalyst of direct borohydride-hydrogen peroxide fuel cell

Au–Co alloys supported on Vulcan XC-72R carbon were prepared by the reverse microemulsion method and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The physical and electrochemical properties were investigated by energy dispersive X-ray (EDX), X-ray diffraction (XRD), cyclic voltammetry, chronamperometry and chronopotentiometry. The results show that supported Au–Co alloys catalysts have higher catalytic activity for the direct oxidation of BH₄⁻ than pure nanosized Au catalyst, especially the Au₄₅Co₅₅/C catalyst presents the highest catalytic activity among all as-prepared Au–Co alloys, and the DBHFC using the Au₄₅Co₅₅/C as anode electrocatalyst shows as high as 66.5 mW cm⁻² power density at a discharge current density of 85 mA cm⁻² at 25 °C.     

Pt–Ru catalysts supported on carbon xerogels for PEM fuel cells

Pt–Ru electrocatalysts supported on carbon xerogels were synthesized by reduction of metal precursors with formate ions (SFM method). The carbon xerogel was chemically and heat treated in order to evaluate the different procedures to generate oxygenated groups on the surface. Temperature-programmed desorption (TPD) of xerogels showed that heat treatment of previously chemically modified support gradually removes the oxygenated groups from the carbon surface. Physical characterization of the catalyst was performed using X-ray dispersive energy (EDX) and X-ray diffraction (XRD) techniques. Results confirmed that Pt–Ru catalysts with similar metal content (20%) and atomic ratios (Pt:Ru 1:1) were obtained.     

Ultrafine amorphous Co–W–B alloy as the anode catalyst for a direct borohydride fuel cell

The ultrafine amorphous Co–W–B alloy has been synthesized by chemical reduction and used as anode catalyst in direct borohydride fuel cell. The results show that the maximum power output of the cell is 101 mW cm⁻² at 15 °C, and the essential power density of this material can be up to 350 mW cm⁻² at 15 °C and 500 mW cm⁻² at 60 °C, respectively. The cell has also a good durability, with no attenuation observed after one week of operation.     

CO tolerant PtRu–MoOx nanoparticles supported on carbon nanofibers for direct methanol fuel cells

Novel nanostructured catalysts based on PtRu–MoO_x nanoparticles supported on carbon nanofibers have been investigated for CO and methanol electrooxidation. Carbon nanofibers are prepared by thermocatalytic decomposition of methane (NF), and functionalized with HNO₃ (NF.F). Electrocatalysts are obtained using a two-step procedure: (1) Pt and Ru are incorporated on the carbon substrates (Vulcan XC 72R, NF and NF.F), and (2) Mo is loaded on the PtRu/C samples. Differential electrochemical mass spectrometry (DEMS) analyses establish that the incorporation of Mo increases significantly the CO tolerance than respective binary counterparts. The nature of the carbon support affects considerably the stabilization of MoO_x nanoparticles and also the performance in methanol electrooxidation. Accordingly, a significant increase of methanol oxidation is obtained in PtRu–MoO_x nanoparticles supported on non-functionalized carbon nanofiber, in parallel with a large reduction of the Pt amount in comparison with binary counterparts and commercial catalyst.     

Characterization and performance evaluation of Pt–Ru electrocatalysts supported on different carbon materials for direct methanol fuel cells

The paper addresses the effect of the carbon support on the microstructure and performance of Pt–Ru-based anodes for direct methanol fuel cells (DMFC), based on the study of four electrodes with a carbon black functionalized with HNO₃, a mesoporous carbon (CMK-3), a physical mixture of TiO₂ and carbon black and a reference carbon thermally treated in helium atmosphere (HeTT). It is shown that CMK-3 hinders the growth of the electrocatalyst nanoparticles (2.7 nm) and improves their distribution on the support surface, whereas the oxidized surfaces of HNO₃ carbon and TiO₂+carbon lead to larger (4–4.5 nm), agglomerated particles, and the lowest electrochemical active areas (54 and 26 m² g⁻¹, in contrast with 90 m² g⁻¹ for CMK-3), as determined from CO stripping experiments. However, HNO₃ and TiO₂ are characterized by the lowest CO oxidation potential (0.4 V vs. RHE), thus suggesting higher CO tolerance for the se electrodes. Tests in DMFC configuration show that the three modified electrodes have clearly better performance than the reference HeTT. The highest power density attained with electrodes supported on carbon treated with HNO₃ (65 mW cm⁻²/300 mA cm⁻² at 90 °C) and the equally interesting performance of the TiO₂-based electrodes (53 mW cm⁻²/300 mA cm⁻²), is a strong indication of the positive effect of the presence of oxygenated groups on the methanol oxidation reaction. The results are interpreted in order to identify separate microstructural (electrocatalyst particle size, porosity) and compositional (oxygenated surface groups, presence of oxide phase) effects on the electrode performance.     

Hydrogen generation from LiBH4 solution catalyzed by multiwalled carbon nanotubes supported Co–B nanocatalysts for a portable micro proton exchange membrane fuel cell application

LiBH₄ has high hydrogen storage capacities, and could potentially serve as a superior hydrogen storage material. In the hydrolytic process, however, incomplete hydrolysis caused by the agglomeration of its hydrolytic product and un-reacted LiBH₄ limits its full utilization. Furthermore, application of hydrogen generated from LiBH₄ aqueous solution for proton exchange membrane fuel cell (PEMFC) has not been reported yet. In this paper, CNTs-supported Co–B nanocatalyst was used for hydrogen generation from LiBH₄ solution. 22 wt% LiBH₄ alkaline solution can fully release its stoichiometric amount of hydrogen and supply a 2.3 W portable PEMFC stack to run stably. The overall power density of the PEMFC/LiBH₄ solution system with Co–B/CNTs addition is 1020 Wh L⁻¹. Due to the high gravimetric and volumetric hydrogen capacities, the LiBH₄ solution could be used as a promising liquid hydrogen storage material for hydrogen fuel cells-based devices.     

Development of a power management unit for small portable direct borohydride fuel cell–NiMH battery hybrid system

In this study, a small portable fuel cell/battery hybrid system has been developed. The system consists of a single portable direct borohydride/peroxide fuel cell (DBPFC), NiMH battery and power management unit (PMU). The battery has been used as a primary power source and has been discharged at constant load. When its state of charge is reduced, the DBPFC charges the battery and powers the load simultaneously. A DC–DC Boost converter has been used as a PMU. The DBPFC has provided the total power of 0.21 Wh into the system during the charge. During this experimental study fuel (NaBH₄) efficiency of 37% has been achieved in the hybrid system, while the system efficiency has been calculated as 34.5%.     

High-performance cobalt–tungsten–boron catalyst supported on Ni foam for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are highly wanted in developing on-demand hydrogen generation system for practical onboard application. By using a modified electroless plating method, we have prepared a robust Co–W–B amorphous catalyst supported on Ni foam (Co–W–B/Ni foam catalyst) that is highly effective for catalyzing hydrogen generation from alkaline NaBH₄ solution. It was found that the plating times, calcination temperature, NaBH₄ and NaOH concentrations all exert considerable influence on the catalytic effectiveness of Co–W–B/Ni foam catalyst towards the hydrolysis reaction of NaBH₄. Via optimizing these preparation and reaction conditions, a hydrogen generation rate of 15 L/min g (Co–W–B) has been achieved, which is comparable to the highest level of noble metal catalyst. In consistent with the observed pronounced catalytic activity, the activation energy of the hydrolysis reaction using Co–W–B/Ni foam catalyst was determined to be only 29 kJ/mol. Based on the phase analysis and structural characterization results, the mechanism underlying the observed dependence of catalytic effectiveness on the calcination temperature was discussed.     

Carbon supported platinum–gold alloy catalyst for direct formic acid fuel cells

The Pt–Au nanoparticles with 1:1 atomic ratio supported on carbon powder were prepared by the co-reduction method using N,N-dimethylformamide coordinated Pt–Au complex as a precursor. Cyclic voltammetry results demonstrated that the PtAu/C catalyst exhibited a higher activity for the formic acid oxidation reaction than did the commercial Pt/C catalyst, reflected by its lower onset potential and higher peak current. The fuel cell performance test at 60 °C showed that the direct formic acid fuel cell with the PtAu/C catalyst yielded about 35% higher power density than did the cell with the Pt/C catalyst.     

One-pot sol–gel synthesis of Ni/TiO2 catalysts for methane decomposition into COx free hydrogen and multiwalled carbon nanotubes

A series of mesoporous Ni/TiO₂ catalysts with different loadings of nickel from 10 to 50 wt% was successfully prepared via a facile one-pot sol–gel route; characterized for its structural, textural and redox properties; and tested for the non-oxidative thermocatalytic decomposition of undiluted methane for the first time. The characterization results reveal the presence of both NiO and NiTiO₃ and metallic nickel as active metal phase in the fresh and reduced catalysts, respectively. Spherical catalyst particles were found to be highly inter-aggregated and to provide a porous texture to the catalyst. All of the prepared catalysts exhibited high catalytic activity and stability for methane decomposition. It is due to the fine dispersion of active nickel nanoparticles on the surface of the TiO₂ support with proper metal-support interaction. Moreover, with increasing nickel loading and reaction temperature, the yields of hydrogen and nanocarbon were found to be significantly increased. A maximum hydrogen yield of 56% and a final carbon yield of 1544% were obtained for the 50% Ni/TiO₂ catalyst at 700 °C with an undiluted methane feed of 150 ml/min for 360 min of time on stream. The catalyst showed high catalyst stability, for a period of 960 min of time on stream and ～24% hydrogen yield was observed at the end of long-term run using the 50% Ni/TiO₂ catalyst. Moreover, irrespective of the nickel loading involved, bulk amount of multiwalled carbon nanotubes were deposited on the surface of the catalyst. XRD and Raman analyses of the spent catalysts showed that the crystallinity of nanocarbon increased with increasing nickel loadings, whereas the graphitization degree remained unaffected, with an I_D/I_G value of 0.88.