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%.     

A direct borohydride-peroxide fuel cell-LiPO hybrid motorcycle prototype: Investigation of short-term behavior of DBPFC stack – I

In the present study, a safer and more performance 270?W Direct Borohydride/Peroxide Fuel Cell (DBPFC) Stack has been constructed for an electrical hybrid motorbike application. Performance tests were carried out with single cell and 5–10–25?cell stacks. Performance loss has been not observed while stacking DBPFC because of the Independent Cell Liquid Distribution Network (ICLDN) system and special bipolar plate design. The power densities have been approximately 120?mWcm^?2 for a single DBPFC and 25-cell DBPFC stack without any stacking loss. Additionally, the stack temperature has been controlled by keeping the oxidant concentration low, and it has been maintained at approximately 52?°C without using a cooling system. The short-term performances of the 25-cell DBPFC stack have been tested over 25?min and 50?min, which showed that the performance and stack security of the DBPFC are highly related to the oxidant properties, such as the concentration, temperature and feed type.     

Electrocatalysts supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cell

Electrocatalysts of Rh, Ru, Pt, Au, Ag, Pd, Ni, and Cu supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cells are investigated. Metal/γ-Al₂O₃ catalysts for NaBH₄ and H₂O₂ decomposition tests are manufactured and their catalytic activities upon decomposition are compared. Also, the effects of XC-72 and multiwalled carbon nanotube (MWCNT) carbon supports on fuel cell performance are determined. The performance of the catalyst with MWCNTs is better than that of the catalyst with XC-72 owing to a large amount of reduced Pd and the good electrical conductivity of MWCNTs. Finally, the effect of electrodes with various catalysts on fuel cell performance is investigated. Based on test results, Pd (anode) and Au (cathode) are selected as catalysts for the electrodes. When Pd and Au are used together for electrodes, the maximum power density obtained is 170.9 mW/cm² (25 °C).     

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.     

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.     

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.     

Nonlinear control of fuel cell hybrid power sources: Part II – Current control

In this paper is proposed a nonlinear current-mode control for the fuel cell/battery/ultracapacitor hybrid power sources (HPS) that improves the ripple factor of the fuel cell current. The nonlinear current control is analyzed and designed using a systematic approach. The design goal is to generate an anti-ripple via buck current controlled source in order to mitigate the inverter current ripple. All the results have been validated in several simulations. The simulation results successfully show that nonlinear current-mode control determines in the low frequency-domain better performances than other current-mode control techniques, such as the hysteretic current-mode controller or the peak current-mode controller. The current ripple factor is one of the used performance indicators.     

A novel direct methanol fuel cell with sol–gel flux phase

The sol–gel flux phase of direct methanol fuel cell is prepared by the modified sol–gel method with starting materials of Na₂SiO₃ or Si(OCH₃)₄, methanol and sulfuric acid, and characterized by SEM. The methanol permeability and electrochemical characteristics of the sol–gel flux phase are investigated. The mass transportation mechanism and the process of methanol has been changed by the porous structure of the sol–gel flux phase. The methanol permeability of the sol–gel flux phase decreases more than 90% compared with the liquid flux phase of 1 mol L^?1 CH₃OH and 1 mol L^?1 H₂SO₄. A novel direct methanol fuel cell with sol–gel flux phase is designed. The power density of which is higher than that of the cell with liquid flux phase.     

Power coordination in a fuel cell–battery hybrid power source using commercial power controller circuits

Hybrid power systems combine the superb energy density of a fuel cell power source with the outstanding power density of modem batteries. A hybrid power source with an integral power distribution and charge management system was designed and built using standard miniature power regulator integrated circuits with appropriate modifications to implement the necessary controls. The resulting converter not only allows the interconnection of fuel cell systems and batteries having dissimilar operating voltages, but it also imposes a power sharing strategy that elicits peak performance from each part of the device. The resulting hybrid power source can supply 70% greater peak power, with only a 6% increase in weight, and no increase in volume, compared to the as-packaged fuel cell power source on which the hybrid source was based.     

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.     

Enhanced performance of direct peroxide–peroxide fuel cells by employing three-dimensional Ni and Co@TiC nanoarrays anodes

Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H₂O₂ oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H₂O₂ electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm^?2 at 0.3 V in 1.0 M H₂O₂ + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm^?2 and open circuit voltage of 0.90 V at 85.1 mA cm^?2 with desirable cell stability at 10 mL min^?1 flow rate and 20 °C, which is much higher than those previously reported.     

A high energy density lithium/sulfur–oxygen hybrid battery

In this paper we introduce a lithium/sulfur–oxygen (Li/S–O₂) hybrid cell that is able to operate either in an air or in an environment without air. In the cell, the cathode is a sulfur–carbon composite electrode containing appropriate amount of sulfur. In the air, the cathode first functions as an air electrode that catalyzes the reduction of oxygen into lithium peroxide (Li₂O₂). Upon the end of oxygen reduction, sulfur starts to discharge like a normal Li/S cell. In the absence of oxygen or air, sulfur alone serves as the active cathode material. That is, sulfur is first reduced to form a soluble polysulfide (Li₂S_x, x ≥ 4) that subsequently discharges into Li₂S through a series of disproportionations and reductions. In general, the Li/S–O₂ hybrid cell presents two distinct discharge voltage plateaus, i.e., one at ～2.7 V attributing to the reduction of oxygen and the other one at ～2.3 V attributing to the reduction of sulfur. Since the final discharge products of oxygen and sulfur are insoluble in the organic electrolyte, it is shown that the overall specific capacity of Li/S–O₂ hybrid cell is determined by the carbon composite electrode, and that the specific capacity varies with the discharge current rate and electrode composition. In this work, we show that a composite electrode composed by weight of 70% M-30 activated carbon, 22% sulfur and 8% polytetrafluoroethylene (PTFE) has a specific capacity of 857 mAh g^?1 vs. M-30 activated carbon at 0.2 mA cm^?2 in comparison with 650 mAh g^?1 of the control electrode consisting of 92% M-30 and 8% PTFE. In addition, the self-discharge of the Li/S–O₂ hybrid cell is expected to be substantially lower when compared with the Li/S cell since oxygen can easily oxidize the soluble polysulfide into insoluble sulfur.     

Performance of organic–inorganic hybrid anion-exchange membranes for alkaline direct methanol fuel cells

A series of organic–inorganic membranes were prepared through sol–gel reaction of quaternized poly(vinyl alcohol) (QAPVA) with different contents of tetraethoxysilanes (TEOS) for alkaline direct methanol fuel cells. These hybrid membranes are characterized by FTIR, X-ray diffraction (XRD), scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDXA) and thermo gravimetric analysis (TGA). The ion exchange content (IEC), water content, methanol permeability and conductivity of the hybrid membranes were measured to evaluate their applicability in fuel cells. It was found that the addition of silica enhanced the thermal stability and reduced the methanol permeability of the hybrid membranes. The hybrid membrane M-5, for which the silica content was 5 wt%, showed the lowest methanol permeability and the highest ion conductivity among the three hybrid membranes. The ratio of conductivity to methanol permeability of the membrane M-5 indicated that it had a high potential for alkaline direct methanol fuel cell applications.     

Nonlinear control of fuel cell hybrid power sources: Part I – Voltage control

In this paper is proposed a nonlinear control for fuel cell/battery/ultracapacitor hybrid power sources (HPS) that improves the performance and durability of fuel cell. The nonlinear voltage control is analyzed and designed using a systematic approach. The design goal is to stabilize the HPS output voltage at a low voltage ripple that is also spread in a large frequencies band. All the results have been validated in several simulations. The simulation results successfully show that nonlinear voltage control performs good performances in the frequency-domain (a high spreading level of power spectrum) and in the time domain (a low level of output voltage ripple factor), too.     

Carbon-supported Pd–Ir catalyst as anodic catalyst in direct formic acid fuel cell

It was reported for the first time that the electrocatalytic activity of the Carbon-supported Pd–Ir (Pd–Ir/C) catalyst with the suitable atomic ratio of Pd and Ir for the oxidation of formic acid in the direct formic acid fuel cell (DFAFC) is better than that of the Carbon-supported Pd (Pd/C) catalyst, although Ir has no electrocatalytic activity for the oxidation of formic acid. The potential of the anodic peak of formic acid at the Pd–Ir/C catalyst electrode with the atomic ratio of Pd and Ir = 5:1 is 50 mV more negative than that and the peak current density is 13% higher than that at the Pd/C catalyst electrode. This is attributed to that Ir can promote the oxidation of formic acid at Pd through the direct pathway because Ir can decrease the adsorption strength of CO on Pd. However, when the content of Ir in the Pd–Ir/C catalyst is too high the electrocatalytic activity of the Pd–Ir/C catalyst would be decreased because Ir has no electrocatalytic activity for the oxidation of formic acid.     

Graphene nanosheet–CNT hybrid nanostructure electrode for a proton exchange membrane fuel cell

This work demonstrates two-step growth of graphene nanosheets (GNS), in which carbon nanotubes (CNTs) are grown directly on a carbon cloth. GNS are subsequently constructed on the CNT surface, revealing the stand-up structure of the GNS–CNT hybrid nanostructure. The GNS–CNT hybrid nanostructure shows Nernstian and fast electron-transfer kinetics for electrochemical reactions of Fe(CN)₆^3−/4−. A 0.1 mg cm⁻² Pt/GNS–CNT is used in the cathode of a proton membrane exchange fuel cell, in which the maximum power density is 1072 mW cm⁻² at 80 °C under H₂/O₂. In addition to a low-resistance electron-transfer pathway, the GNS–CNT hybrid nanostructure also provides numerous edge planes with strong electrochemical activity, ultimately enhancing electrochemical activity and fuel cell performance.     

Design,elaboration and characterization of a Ni–MH battery prototype

This paper shows advances achieved in the design and construction of a nickel–metal hydride (Ni–MH) battery prototype. The requirements of the design were to characterize the new variables appearing in a commercially assembled battery, such as limited physical space, electrical contact resistance, the behaviour of the system as a function of the gas evolution during fast charge and overcharge, and others. The electrochemical characterization was performed using laboratory equipment.     

Comparison between two optimization strategies for solid oxide fuel cell–gas turbine hybrid cycles

This paper compares the performance characteristics of a combined power system with solid oxide fuel cell (SOFC) and gas turbine (GT) working under two thermodynamic optimization strategies. Expressions of the optimized power output and efficiency for both the subsystems and the SOFC-GT hybrid cycle are derived. Optimal performance characteristics are discussed and compared in detail through a parametric analysis to evaluate the impact of multi-irreversibilities that take into account on the system behaviour. It is found that there exist certain new optimum criteria for some important design and operating parameters. Engineers should find the methodologies developed in this paper useful in the optimal design and practical operation of complex hybrid fuel cell power plants.