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).     

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.     

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.     

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.     

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.     

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.     

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.     

Evaporator modeling – A hybrid approach

In this paper, a hybrid modeling approach is proposed to model two-phase flow evaporators. The main procedures for hybrid modeling includes: (1) Based on the energy and material balance, and thermodynamic principles to formulate the process fundamental governing equations; (2) Select input/output (I/O) variables responsible to the system performance which can be measured and controlled; (3) Represent those variables existing in the original equations but are not measurable as simple functions of selected I/Os or constants; (4) Obtaining a single equation which can correlate system inputs and outputs; and (5) Identify unknown parameters by linear or nonlinear least-squares methods. The method takes advantages of both physical and empirical modeling approaches and can accurately predict performance in wide operating range and in real-time, which can significantly reduce the computational burden and increase the prediction accuracy. The model is verified with the experimental data taken from a testing system. The testing results show that the proposed model can predict accurately the performance of the real-time operating evaporator with the maximum error of ±8%. The developed models will have wide applications in operational optimization, performance assessment, fault detection and diagnosis.     

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.     

Microbial fuel cell – A novel self-powered wastewater electrolyser for electrocoagulation of heavy metals

This paper describes the suitability of the Microbial Fuel Cell (MFC) for generation of electrical power with a simultaneous synthesis of active catholyte in the form of caustic solution. The active solution formed inside a terracotta based MFC reactor was a product of self-powered wastewater electrolysis utilizing i) wastewater with added sodium acetate as a carbon source and ii) neat urine. The catholyte solution that has been actively synthesized was harvested and used for precipitation of heavy metals such as: iron, copper and zinc showing its suitability for use in electro-coagulation (electro-flocculation). This proposed alternative approach to self-powered electrocoagulation is based on electrochemically formed caustic catholyte within the inner cathode chamber of the MFC and then used ex situ to form metal hydroxides that precipitate out from heavy metal solutions.     

Non-stoichiometric tungsten-carbide-oxide-supported Pt–Ru anode catalysts for PEM fuel cells – From basic electrochemistry to fuel cell performance

Durability and cost of Proton Exchange Membrane fuel cells (PEMFCs) are two major factors delaying their commercialization. Cost is associated with the price of the catalysts, while durability is associated with degradation and poisoning of the catalysts, primarily by CO. This motivated us to develop tungsten-carbide-oxide (W_xC_yO_z) as a new non-carbon based catalyst support for Pt–Ru–based anode PEMFC catalyst. The aim was to improve performance and obtain higher CO tolerance compared to commercial catalysts. The performance of obtained PtRu/W_xC_yO_z catalysts was investigated using cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry. Particular attention was given to the analysis of CO poisoning, to better understand how W_xC_yO_z species can contribute to the CO tolerance of PtRu/W_xC_yO_z. Improved oxidation of CO_ads at low potentials (E < 0.5 V vs. RHE) was ascribed to OH provided by the oxide phase at the interfacial region between the support and the PtRu particles. On the other hand, at high potentials (E > 0.5 V vs. RHE) CO removal proceeds dominantly via OH provided from the oxidized metal sites. The obtained catalyst with the best performance (30% PtRu/W_xC_yO_z) was tested as an anode catalyst in PEM fuel cell. When using synthetic reformate as a fuel in PEMFC, there is a significant power drop of 35.3 % for the commercial 30% PtRu/C catalyst, while for the PtRu/W_xC_yO_z anode catalyst this drop is around 16 %.     

Anthracite pretreatment for high-performance direct carbon solid oxide fuel cell — A green pathway for power generation

Coal-fueled direct carbon solid oxide fuel cell (DC-SOFC) is a very attractive electrochemical conversion device. However, coal contains a certain amount of ash, such as Al, Si, S, etc., which are toxicants for SOFC components. To solve the above problem, anthracite is pyrolyzed at 600 °C to obtain semi-coking coal results in better cell performance. The results show that the higher carbon gasification oxidation activity of semi-coking coal is due to the higher amount of fixed carbon and catalyst. Therefore, more fuel gas (CO) is available in the anode chamber for the Boudouard reaction. Also, the electrochemical performance of both coals as DC-SOFC fuel was compared using La_0·4Sr_0·6Co_0·2Fe_0·7Nb_0·1O_3-δ (LSCFN) as anode. The maximum power density (MPD) of the DC-SOFC with semi-coking coal is 596 mW cm⁻² at 850 °C, much higher than that of the SOFC using anthracite (396 mW cm⁻²) as the fuel. Furthermore, at the same fuel content, the cell fueled with semi-coking coal has a longer discharge time (30 h), which shows a better stability.     

Performance studies of Pd–Pt and Pt–Pd–Au catalyst for electro-oxidation of glucose in direct glucose fuel cell

Platinum is employed as anode catalyst for low temperature electro-oxidation of glucose in direct glucose fuel cell (DGFC), but it suffers from poisoning by intermediate oxidation products. In the present investigation, palladium and gold precursors are added with platinum precursor to form low metal loading (∼15–20% by wt.) carbon supported catalyst by NaBH₄ reduction technique. The prepared PtPdAu/C (metal ratio 1:1:1) and PdPt/C (metal ratio 4:1) catalysts are tested in DGFC. The Physical characterization of electro-catalysts by scanning electron microscope, transmission electron microscope, energy dispersive X-ray, X-ray diffraction and thermo-gravimetric analysis confirms the formation of nano-sized metal particles on carbon substrate with two prominent homogeneous bi- or tri-metallic crystal phases for PtPdAu/C. The cyclic voltammetry studies carried out for glucose (0.05 M) oxidation in (0.5 M KOH) alkaline medium shows the metal catalysts can efficiently electro-oxidize glucose. The catalysts tested as anode in a batch type DGFC using commercial activated charcoal as cathode produced peak power density of 0.52 mW cm⁻² for both PdPt/C and PtPdAu/C in 0.3 M glucose in 1 M KOH solution.     

Nafion/Pd–SiO2 nanofiber composite membranes for direct methanol fuel cell applications

One of the major challenges for direct methanol fuel cells is the problem of methanol crossover. With the aim of solving this problem without adverse effects on the membrane conductivity, Nafion/Palladium–silica nanofiber (N/Pd–SiO₂) composite membranes with various fiber loadings were prepared by a solution casting method. The silica-supported palladium nanofibers had diameters ranging from 100 nm to 200 nm and were synthesized by a facile electro-spinning method. The thermal properties, ionic exchange capacities, water uptake, proton conductivities, methanol permeabilities, chemical structures, and micro-structural morphologies were determined for the prepared membranes. It was found that the transport properties of the membranes were affected by the fiber loading. All of the composite membranes showed higher water uptake and ion exchange capacities compared to commercial Nafion 117 and proved to be thermally stable for use as proton exchange membranes. The composite membranes with optimum fiber content (3 wt%) showed an improved proton conductivity of 0.1292 S cm⁻¹ and a reduced methanol permeability of 8.36 × 10⁻⁷ cm² s⁻¹. In single cell tests, it was observed that, the maximum power density measured with composite membrane is higher than those of commercial Nafion 117.