The affects of membrane on the cell performance when using alkaline borohydride–hydrazine solutions as the fuel

The cell performance and the polarization behavior of the fuel cell using alkaline NaBH₄–N₂H₄ solutions as the fuel were investigated. It was found that the use of different membrane: anion exchange membrane (AEM) or cation exchange membrane (CEM) would influence the cell performance and cathode polarization behavior. The direct borohydride fuel cell (DBFC) using CEM gave a higher power density than that using AEM, but the direct hydrazine fuel cell (DHFC) using CEM gave a lower power density compared with the DHFC using AEM. In the DBFCs using CEM, N₂H₄ addition in alkaline NaBH₄ solution improved the cell performance but it did not make any difference when adding more N₂H₄. On the other hand, in the DBFCs using AEM, cell performance was improved with increasing the amount of N₂H₄ in the anolyte.     

Electrochemical preparation and characterization of C/Ni–NiIr composite electrodes as novel cathode materials for alkaline water electrolysis

The binary NiIr coatings as novel and effective catalysts were electrochemically prepared on a Ni-modified carbon felt electrode (C/Ni–NiIr) in view of their possible application as cathode materials for the alkaline water electrolysis. The surface morphology and chemical composition of the electrodes were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. Their hydrogen evolution activity was assessed by electrochemical techniques. It was found that, the preparation of NiIr co-deposits on the Ni-modified C substrate enhances the hydrogen evolution activity. The electrodes have wide space, which is an advantage for diffusion of ions and hydrogen bubbles through inner zones and reduction of diffusion resistance. The high hydrogen evolution activity of the C/Ni–NiIr electrode was mainly attributed to the finer surface structure, high surface area and the higher numbers of the catalytically active centers.     

Preparation and characterization of positive electrode of Ni–MH batteries with cobalt additives

The present paper shows the preparation and characterization of alkaline batteries cathodes formed by nickel hydroxide with the addition of cobalt. This additive was incorporated by two methods: on the electrode surface, using the electroless technique and by direct incorporation of cobalt powder in the active material. The electrochemical behavior of both nickel hydroxide electrodes was investigated and compared. The results indicate that active materials containing cobalt additive by the electroless technique exhibit an improvement on the electrochemical performance.     

Corrosion characteristics and fuel cell performance of a cost-effective high Mn–Low Ni austenitic stainless steel as an alternative to SS 316L bipolar plate

In this study, newly developed high manganese (Mn) and low nickel (Ni) austenitic stainless steels were investigated as an alternative to conventionally used SS 316L for bipolar plate applications in proton exchange membrane fuel cells. Systematic studies on the corrosion behavior were carried out in simulated hydrogen and oxygen environments, for both half- and fuel-cell conditions. The Mn-based SS revealed nobler corrosion potential and comparable passive current densities to that of SS 316L. The passive current density of Mn-based SS is well within the DoE 2020 target of <1 μA cm⁻². Though MnSS1 steel has lean Ni content, the addition of Mn and N is beneficial for improving the corrosion performance, which is comparable to SS 316L. The recorded ICR values for Mn SS1 and SS 316L are 234.6 ± 20 and 155 ± 20 mΩ cm² at a compaction force of 140 N cm⁻², respectively. Both the steels do not to meet the DoE ICR target of 10 mΩ cm², which requires conductive coating or improvement in oxide conductivity. The performances of the steels (both Mn-SS and 316L SS) with varying thickness were also investigated in a single fuel cell condition with serpentine flow field design as bipolar plates with varying thickness (10, 5 and 2 mm). A maximum power density of 370 mW cm⁻² was achieved with the Mn-based metallic bipolar plates, whereas SS 316L showed 354 mW cm⁻². By changing the composition of austenitic stainless steel, that is, using Mn SS1 instead of SS 316L the overall fuel cell cost decreases by three times.     

Effects of Co3O4 as additive on the performance of metal hydride electrode and Ni–MH battery

In this paper, the performance of metal hydride electrodes prepared with different amounts of tricobalt tetraoxide (Co₃O₄) and AA size cylindrical Ni–MH battery with the capacity of 1500 mAh prepared with Co₃O₄ as negative additive has been investigated. The investigation reveals that the charge and discharge efficiency at 1400 mA g⁻¹ at room temperature, and the discharge efficiency at 140 mA g⁻¹ at −20 °C of metal hydride electrode are increased from 82.2% to 92.4%, from 55.1% to 84.7%, and from 30.2% to 68.8%, respectively, by adding proper amounts of Co₃O₄. Furthermore, it is also found that the high-rate and low-temperature discharge ability, overcharge endurance ability, cycle life, inner pressure of battery are greatly improved by adding Co₃O₄. These results can be attributed to the high electrocatalytic activity and extended hydride storage capability of Co₃O₄, the improvement of gas consumption ability and the restraining of oxidation of electrode alloys by adding Co₃O₄.     

Effect of KOH concentration and anions on the performance of an NiH2 battery positive plate

The capacity and voltage behavior of electrochemically impregnated sintered nickel positive plates was examined by galvanostatic charging and discharging in a flooded electrolyte cell. Three different concentrations of potassium hydroxide (KOH) (40%,31% and 26%) and 31% KOH containing dissolved nitrate, sulfate, or silicate were investigated. The end-of-charge voltage at $\text{C}\text{10}$ charge and at 10°C showed the following order: 40% KOH > 31 % KOH alone, and in the presence of the anions > 26% KOH. The mid-discharge voltage at $\text{C}\text{2}$ discharge was higher in 26% KOH, almost the same for 31%Ao KOH with and without the added contaminants, and much lower for 40% KOH. The plate capacity was marginally affected by cycling in all cases except for 40% KOH, where the capacity declined after 1000 cycles at 80% depth-of-discharge (DOD). At the end of cycling all the plates tested experienced a weight loss, except in the case of 31% KOH, as a result of active material extrusion. Cyclic voltammetry of miniature electrodes in 31% KOH showed that the cathodic peak potentials are less polarized at −5 °C (compared to 25 °C) in the presence and absence of silicate. This indicates a slightly higher voltage during discharge in an NiH₂ battery. Furthermore, the features of the current-potential profile were practically unchanged in the presence of silicate.     

Effect of carbon substrate materials as a Pt–Ru catalyst support on the performance of direct methanol fuel cells

The support effect of carbon nanotubes (CNTs) for direct methanol fuel cell (DMFC) was studied using CNTs with and without defect preparation, carbon black, and fishbone-type CNTs. The Pt–Ru/defect-free CNTs afforded the highest catalytic activity of methanol oxidation reaction (MOR) in rotating disk electrode experiments and the highest performance as the anode catalysts in DMFC single cell tests with the one-half platinum loading compared to Pt–Ru/VulcanXC-72R. CO stripping voltammograms with Pt–Ru/defect-free CNTs also revealed the lowest CO oxidation potential among other Pt–Ru catalysts using different carbon support. It is thus considered that the carbon substrates significantly affect the CO oxidation activity of anode electrocatalysts in DMFC. This is ascribed to the geometrical effect that the flat interface between CNTs and metal catalysts has a unique feature, at which the electron transfer occurs, and this interface would modify the catalytic properties of Pt–Ru particles.     

Ag–polytetrafluoroethylene composite coating on stainless steel as bipolar plate of proton exchange membrane fuel cell

Forming a coating on metals by surface treatment is a good way to get high performance bipolar plate of proton exchange membrane fuel cell (PEMFC). In our research, Ag–polytetrafluoroethylene (PTFE) composite film was electrodeposited with silver-gilt solution of nicotinic acid by a bi-pulse electroplating power supply on 316 L stainless steel bipolar plate of PEMFC. Surface topography, contact angle, interfacial conductivity and corrosion resistance of the bipolar plate samples were investigated. Results showed that the defects on the Ag–PTFE composite coating are greatly reduced compared with those on the pure Ag coating fabricated under the same condition; and the contact angle of the Ag–PTFE composite coating with water is 114°, which is much bigger than that of the pure Ag coating (73°). In addition, the interfacial contact resistance of the composite coating stays as low as the pure Ag coating; and the bipolar plate sample with composite coating shows a close corrosion resistance to the pure Ag coating sample in potentiodynamic and potentiostatic tests. Coated 316 L stainless steel plate with Ag–PTFE composite coating exhibits well hydrophobic characteristic, less defects, high interfacial conductivity and good corrosion resistance, which shows a great potential of the application in PEMFC.     

Modeling the performance of an aluminum–air cell

A mathematical model for analysis and prediction of the performance of the aluminum–air cell has been developed. The model takes into account the kinetics of the anode, cathode, and parasitic reactions. Ohmic losses in the electrolyte and mass transfer are also taken into account. The model prediction of cell performance shows good agreement with experimental data. The mathematical model provides detailed information about cell performance for a wide range of operating and design parameters. For better cell performance, our model studies suggest the use of higher electrolyte flow rates, smaller cell gaps, higher conductivities, lower parasitic current densities and operation at moderate current density. From our analysis, we have determined that, in an aluminum air cell, only the activation and ohmic overpotential are important.     

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.     

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.     

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.     

Leveraging in-situ formation of Ni–Fe nanoparticles to promote the catalytic performance of Ruddlesden-Popper based electrode for symmetrical solid oxide fuel cells

Ruddlesden?Popper layered oxide, La_0.25Sr_2.75FeNiO_7-δ (LSFN) is evaluated as a potential electrode material for symmetrical solid oxide fuel cells. The in-situ formation of Ni–Fe alloy nanoparticles on the LSFN surface in reducing atmosphere can be believed to enhance the activity towards hydrogen oxidation reaction. LSFN exhibit maximum conductivity of 221.2 S/cm and 0.206 S/cm in air and hydrogen environment. Furthermore, LSFN is mixed with GDC powder to form a composite electrode for symmetric solid oxide fuel cells (SSOFC). Results show that with the combination of GDC, the maximum power density of YSZ-based SSOFC enlarges from 232.3 mW cm^?2 to 348.5 mW cm^?2, and related polarization resistance reduces from 0.359 Ω cm² to 0.108 Ω cm². The improved performance is attributed to the enlarged triple-phase boundary with the mixing of GDC. In addition, YSZ-based SSOFC with the LSFN-GDC composite electrode shows a stable performance in intermediate-temperature SSOFCs within 200 h, which indicates that LSFN-GDC composite material is a prospective symmetrical electrode for SSOFC.     

Potentiostatic electrodeposition of cost-effective and efficient Ni–Fe electrocatalysts on Ni foam for the alkaline hydrogen evolution reaction

The hydrogen evolution reaction (HER) using earth-abundant noble-metal-free catalysts has gained substantial interest in electrocatalytic water splitting technologies, particularly in water-alkali electrolyzers. The development of highly-efficiency and durable inexpensive electrocatalysts to accelerate the kinetics of HER is still a formidable challenge. In this study, nickel–iron (Ni–Fe) electrocatalyst directly grown on backbones of Ni foam (NF) substrate was facile prepared via one-step potentiostatic electrodeposition method. The obtained Ni–Fe electrocatalyst exhibits a film-like structure. Owing to high electrical conductivity and composition optimization, the synthesized Ni–Fe electrocatalyst with Ni/Fe atomic ratio of c.a. 65:35 possesses an attractive electrocatalytic activity with low overpotentials of 142, 205, and 239 mV at 10, 50, and 100 mA·cm^?2 in alkaline electrolyte, respectively.     

Flame aerosol synthesis of carbon-supported Pt–Ru catalysts for a fuel cell electrode

This study describes how a flame spray pyrolysis method was successfully used to synthesize PtRu catalysts supported by carbon agglomerates. Nearly spherical catalysts composed of metallic Pt and Ru with molar ratio of 1:1 were produced in the flame and their size was about 1.9 nm. X-ray diffraction measurements revealed that amorphous-like Ru was well mixed into the Pt crystalline lattices. Through cyclic voltammetry for methanol oxidation reaction and CO stripping, it was found that the electrochemical activities of the catalysts produced from this process are comparable to or slightly better than those of an equivalent commercial sample with the same composition.     

Effects of Cu substrate morphology and phase control on electrochemical performance of Sn–Ni alloys for Li-ion battery

The influence of substrate morphology and ageing on the charge–discharge performance of a Sn–Ni alloy anode electrodeposited on a Cu substrate are examined. The Sn–Ni alloy (Sn 82 at.%–Ni 18 at.% anode) shows a high capacity of around 480 mAh g⁻¹ up to 12 cycles, but its capacity rapidly fades with cycling. The initial capacity and the cyclic properties of the alloy electrode are significantly improved when the surface morphology of the Cu substrate is changed from smooth-type to nodule-type. Optimized ageing treatment leads to further enhancement in the charge–discharge performance of the anode. The increase in the capacity and better cyclic properties are attributed to stronger adhesion between the Si–Ni anode and the Cu substrate. This is induced by inter-locking of the nodule-type Cu substrate and a buffering effect of Cu–Sn intermetallic compounds formed during ageing.     

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.     

Ni–P and Ni–Co–P coated aluminum alloy 5251 substrates as metallic bipolar plates for PEM fuel cell applications

This study is aimed to replace graphite bipolar plates in PEM fuel cells with surface modified aluminum alloy. To improve the surface characteristics of aluminum alloy 5251 (AA5251) substrate, Ni–P and Ni–Co–P coatings were deposited using electroless and electroplating deposition techniques [power supply and chronoamperometry]. Surface morphology and chemical composition of prepared coatings have been investigated using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques. The corrosion behaviour of Ni–P and Ni–Co–P coated AA5251 was studied in (0.5 M H₂SO₄ + 2 ppm HF) solution by potentiodynamic polarization technique. Lower corrosion current densities and more positive corrosion potentials were gained after coating AA5251 with Ni–P and Ni–Co–P deposits. Much better corrosion resistance was shown by coatings containing cobalt. Potentiostatic tests were carried out at +160 mV (MMS) in air-saturated solution to simulate cathode environment in PEM fuel cells. The current density of Ni–Co–P (1:1)/AA5251 was stabilized at a value lowered by 4 times relative to that at bare AA5251 substrate. Interfacial contact resistance values between coated substrates and carbon paper were measured. Ni–P and Ni–Co–P coatings prepared by electroless method showed ICR values, twice that at ones prepared by electroplating power supply technique.