ZrO2–SiO2/Nafion composite membrane for polymer electrolyte membrane fuel cells operation at high temperature and low humidity

Recast Nafion^® composite membranes containing ZrO₂–SiO₂ binary oxides with different Zr/Si ratios are investigated for polymer electrolyte membrane fuel cells (PEMFCs) at temperatures above 100 °C. Fine particles of the ZrO₂–SiO₂ binary oxides, same as an inorganic filter, are synthesized from a sodium silicate and a carbonate complex of zirconium by a sol–gel technique. The composite membranes are prepared by blending a 10% (w/w) Nafion^®-water dispersion with the inorganic compound. All composite membranes show higher water uptake than unmodified membranes, and the proton conductivity increases with increasing zirconia content at 80 °C. By contrast, the proton conductivity decreases with zirconia content for the composite membranes containing binary oxides at 120 °C. The composite membranes are tested in a 9-cm² commercial single cell at both 80 °C and 120 °C in humidified H₂/air under different relative humidity (RH) conditions. Composite membrane containing the ZrO₂–SiO₂ binary oxide (Zr/Si = 0.5) give the best performance of 610 mW cm⁻¹ under conditions of 0.6 V, 120 °C, 50% RH and 2 atm.     

Concentration measurements in lithium/polymer–electrolyte/lithium cells during cycling

We report on in situ and ex situ concentration measurements in lithium/polymer–electrolyte/lithium cells during cycling. We have used three different methods which give complementary results, in good agreement with theoretical predictions and previous concentration measurements by Raman confocal microspectroscopy. Our methods allow to obtain concentration maps in the electrolyte, in particular, when dendrites are observed: from these measurements, we can correlate the onset of dendritic growth with local concentration gradients.     

In situ preparation of poly(ethylene oxide)–SiO2 composite polymer electrolytes

Amorphous poly(ethylene oxide) (PEO)–SiO₂ composites are prepared by in situ reactions that involve the simultaneous formation of the polymer network and inorganic nanoparticles. The polymer matrix is formed by ultraviolet irradiation of a PEO macromer, and silica is produced in situ by the sol–gel method. The PEO–SiO₂ composite mixed with LiBF₄ is used as a lithium-ion conducting solid electrolyte and electrochemical transport properties such as ionic conductivity and Li⁺ transference number are measured. A significant increase in the Li⁺ transference number, up to 0.56, is found together with a slight decrease in the ionic conductivity. The results are interpreted in terms of interactions between the surface OH groups of the inorganic particles, the cations, the anions, and the ether oxygen atoms on the PEO backbone.     

Ni–CeO2 composite cathode material for hydrogen evolution reaction in alkaline electrolyte

In this work, nickel-based electrodes were prepared using composite electrodeposition technique in a nickel sulphamate bath containing suspended micro- or nano-sized CeO₂ particles. The prepared Ni–CeO₂ composite electrodes exhibit an enhanced high catalytic activity toward hydrogen evolution reaction (HER) in alkaline solutions. X-ray diffraction patterns indicated that the CeO₂ particles have been successfully incorporated into the Ni matrix and altered the texture coefficient (TC) of the Ni layer. The morphology of the obtained coatings was characterized by Scanning Electron Microscopy, and the CeO₂ content was determined by coupled energy dispersive X-ray spectrometry. The thermal stability of the composite electrodes was analyzed by thermogravimetric and differential scanning calorimetry, showing a good thermal stability. The catalytic activity of the composite electrodes for HER was measured by steady-state polarization and electrochemical impedance spectroscopy techniques in 1.0 M NaOH solution at room temperature. The exchange current density of HER on the Ni–CeO₂ composite electrodes was much higher than that on Ni electrode. EIS results suggested that a synergetic effect on HER may exist between CeO₂ particles and Ni matrix. Compared to nano-CeO_2, the micro-CeO₂ derived composite electrodes showed higher electrochemical activity. The possible correlation among particle size, content and catalytic activity is discussed.     

All-solid-state lithium secondary batteries with oxide-coated LiCoO2 electrode and Li2S–P2S5 electrolyte

All-solid-state lithium secondary batteries using LiCoO₂ active materials coated with Li₂SiO₃ and SiO₂ oxide films and Li₂S–P₂S₅ solid electrolytes were fabricated and their electrochemical performance was investigated. The electrochemical performace of the all-solid-state cells at a high voltage region was highly improved by using oxide-coated LiCoO₂. The oxide coatings are effective in suppressing the formation of an interfacial resistance between LiCoO₂ and the solid electrolyte at a high cutoff voltage of 4.6 V (vs. Li). As a result, charge–discharge capacities and cycle performance at the cutoff voltage were improved. The cell with Li₂SiO₃-coated LiCoO₂ showed a large initial discharge capacity of 130 mAh g⁻¹ and a good capacity retention of 110 mAh g⁻¹ after 50th cycles at the cutoff voltage of 4.6 V (vs. Li).     

Charge–discharge characteristics of LiCoO2/mesocarbon microbeads battery with poly(vinyl chloride)-based composite polymer electrolyte

Polyvinyl chloride (PVC)-based composite polymer electrolyte films consisting of PVC–LiCF₃SO₃–SiO₂ are prepared by the solution-casting method. The electrical properties of the electrolyte are investigated for ionic conductivity and its dependence on temperature. The electrolyte with the highest ionic conductivity is used to fabricate a LiCoO₂/PVC–LiCF₃SO₃–SiO₂/mesocarbon microbeads (MCMB) battery. The charge–discharge characteristics and performance of the battery at room temperature are evaluated to ascertain the effective viability, of these solid electrolytes in lithium-polymer batteries. Battery performances is also investigated at 313, 323 and 333 K.     

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.     

Pr2NiO4–Ag composite cathode for low temperature solid oxide fuel cells with ceria-carbonate composite electrolyte

Pr₂NiO₄–Ag composite was synthesized and evaluated as cathode component for low temperature solid oxide fuel cells based on ceria-carbonate composite electrolyte. X-ray diffraction analysis reveals that the formation of a single phase K₂NiF₄–type structure occurs at 1000 °C and Pr₂NiO₄–Ag composite shows chemically compatible with the composite electrolyte. Symmetrical cells impedance measurements prove that Ag displays acceptable electrocatalytic activity toward oxygen reduction reaction at the temperature range of 500–600 °C. Single cells with Ag active component electrodes present better electrochemical performances than those of Ag-free cells. An improved maximum power density of 695 mW cm⁻² was achieved at 600 °C using Pr₂NiO₄–Ag composite cathode, with humidified hydrogen as fuel and air as the oxidant. Preliminary results suggest that Pr₂NiO₄–Ag composite could be adopted as an alternative cathode for low temperature solid oxide fuel cells.     

Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO₂ catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO₂ catalysts was much longer than Ni–SiO₂ catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO₂ catalysts. The structure of the carbon filaments generated over Ni–SiO₂ and Ni–Fe–SiO₂ was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO₂ catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO₂ catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.     

Au–MnO2/MWNT and Au–ZnO/MWNT as oxygen reduction reaction electrocatalyst for polymer electrolyte membrane fuel cell

Bi-functional catalysts based on Au supported on oxide based nanomaterials for use in fuel cells were evaluated by electrochemical methods for oxygen reduction reaction (ORR) in Polymer Electrolyte Membrane Fuel Cell (PEMFC). Metal oxide coated multi walled carbon nanotubes (MWNTs) (MnO₂/MWNT and ZnO/MWNT) were prepared by reduction of potassium permanganate and oxidation of Zn powder on MWNT surface respectively. Au–MnO₂/MWNT and Au–ZnO/MWNT were prepared by chemical reduction of chloroauric acid on MnO₂/MWNT and ZnO/MWNT. The samples were characterized and linear sweep voltammetric studies were performed in N₂ saturated, O₂ saturated and methanol containing 1 M KOH solution and the results have been discussed. A single fuel cell was also constructed using Au–MnO₂/MWNT and Au–ZnO/MWNT as ORR electrocatalysts. A maximum power density of 45 mW/cm² and 56 mW/cm² was obtained with Au–MnO₂/MWNT and Au–ZnO/MWNT respectively. Additionally, the methanol tolerance of these electrocatalysts has been investigated and results have been discussed.     

Three-dimensional Li2O–NiO–CoO composite thin-film anode with network structure for lithium-ion batteries

Three-dimensional Li₂O–NiO–CoO composite thin-film electrodes deposited on stainless steel substrates were synthesized by the electrostatic spray deposition (ESD) technique at 240 and 295 °C. The morphology of the composite was investigated by scanning electron microscopy. X-ray diffraction indicated that the as-deposited films are composites of Li₂O, NiO and CoO. The effects of the solvent used to dissolve the starting materials on the morphology and electrochemical performance of the thin-film electrodes were also investigated. It was found that the as-deposited thin-film electrodes exhibited a high reversible capacity (>800 mAh g⁻¹ when cycled between 0.01 and 3 V at a cycling rate of 0.5 C), good capacity retention, and outstanding rate capability. The superior electrochemical performance may have resulted from the combination of the very porous structure and the three-dimensional network of the as-deposited thin-film electrodes, which contributed to a high surface area, favoured lithium-ion diffusion, and formed a stable integral structure. The thin-film electrodes could be promising anodes for use in high power and high energy density lithium-ion batteries.     

Novel Ni–ZrO2 catalyst doped with Yb2O3 for ethanol steam reforming

A type of Yb₂O₃ doped Ni–ZrO₂ catalyst for ethanol steam reforming was developed, and displayed excellent catalyzing performance for the selective formation of H₂ and CO₂. Over a Ni_1.25Zr₁Yb_0.8 catalyst, STY(H₂) can maintain stable at the level of 0.396 mol h⁻¹ g⁻¹ (data taken 120 h after the reaction started) under the reaction conditions of 0.5 MPa and 723 K, which was 1.6 times that (0.247 mol h⁻¹ g⁻¹) of the Yb-free counterpart Ni_1.25Zr₁. Characterization of the catalyst revealed that dissolution of an appropriate amount of Yb³⁺ ions in the zirconia host resulted in the formation of the Zr–Yb composite oxide with cubic-ZrO₂ structure, c-(Zr–Yb)O_z, which inhibited effectively the transformation of c-ZrO₂ to thermodynamically more stable m-ZrO₂, thus avoiding sintering of the (Zr–Yb)O_z composite. It was demonstrated that the doping of Yb₂O₃ to Ni–ZrO₂ changed also the valence states or the micro-environments of the Ni-species at the quasi-active surface of the tested catalyst, which was conducive to inhibiting agglomeration of the Ni_x⁰–Niⁿ⁺ species active catalytically, with resulting in maintaining the high metallic nickel dispersion and inhibiting coking. The aforementioned two factors both contributed to improving the activity and operating stability as well as heat-resistant quality of the catalyst.     

Novel heavy duty engine concept for operation dual fuel H2–NH3

A prior paper has presented a novel design of a heavy duty truck engine fuelled with H₂. In this design, the customary in-cylinder Diesel injector and glow plug are replaced with a main chamber fuel injector and a jet ignition pre-chamber. The jet ignition pre-chamber is a small volume that is connected to the in-cylinder through calibrated orifices accommodating another fuel injector and a glow or a spark plug that controls the start of combustion. This design permits to operate the engine in four different modes: traditional compression ignition (CI), diffusion, Diesel-like (M₁); mixed gasoline/Diesel-like (M₂); traditional spark ignition (SI), premixed, gasoline-like (M₃); premixed, homogeneous charge compression ignition HCCI-like (M₄). In the mode diffusion with jet ignition (M₁), an injection occurs in the jet ignition pre-chamber before the main chamber fuel is injected and the engine operates therefore mostly Diesel-like. In the mode mixed diffusion/premixed Diesel/gasoline-like (M₂) an injection occurs in the jet ignition pre-chamber after only part of the main chamber fuel is injected and mixed with air. In the mode premixed with jet ignition (M₃), an injection occurs in the jet ignition pre-chamber after the main chamber fuel is injected and mixed with air and the engine operates gasoline-like. Finally, in the mode premixed without jet ignition (M₄), no injection occurs in the jet ignition pre-chamber and the engine operates HCCI-like. Modelling results have already been presented and discussed with H₂ as the main chamber and pre-chamber fuel. This paper considers the option to accommodate a second main chamber injector that will inject the NH₃ that will then burn in air thanks to the hot combusting gases from the combustion of H₂ and air using the modes M₁ and M₂ described above. The mode M₃ also of interest is not considered here. First results of simulations show the opportunity to achieve better than Diesel fuel energy conversion efficiency thanks to the reduced heat losses of the “cold burning” NH₃ and suggest to perform the experiments needed to further support the findings.     

High-performance Ni–SiO2 for pressurized carbon dioxide reforming of methane

The SiO₂ and Ni–SiO₂ were synthesized via the complex-decomposition method by using different organic acids as the complexing agent and fuel. The Ni-supported SiO₂ from different sources was prepared by the incipient impregnation method. The Ni–SiO₂ and Ni/SiO₂ were comparatively evaluated for carbon dioxide reforming of methane (CDR) under severe conditions of CH₄/CO₂ = 1.0, T = 750 °C, GHSV = 53200 mL g⁻¹ h⁻¹, and P = 0.1–1.0 MPa. The materials were fully characterized by XRD, XPS, TEM, TG-DSC, H₂-TPR, and N₂ adsorption-desorption at −196 °C. It was found that the complexing agent and preparation method of the catalyst significantly affected its surface area, the size and dispersion of Ni, the reduction behavior, and the coking and sintering properties, which determine the activity and stability of the catalyst for CDR. As a result, a highly active and stable Ni–SiO₂ for pressurized CDR was obtained by optimizing the complexing agent.     

(La,Sr)MnO3–(Y,Bi)2O3 composite cathodes for intermediate-temperature solid oxide fuel cells

Yttria-stabilized bismuth oxides (YSB) are cooperated to (La,Sr)MnO₃ (LSM) to form composite cathodes for intermediate-temperature solid oxide fuel cells. The composite electrodes are fabricated with screen-printing technique and characterized using electrochemical impedance spectroscopy. The interfacial polarization resistances (R_p) of the LSM–YSB electrodes on yttria-stabilized zirconia (YSZ), samaria-doped ceria (SDC), and YSB electrolytes are analyzed regarding the electrode composition and operating temperature. R_p decreases with the increase of YSB content up to 80 wt.% in the LSM–YSB composite. When YSZ is used as the electrolyte, the lowest R_p is 0.14 Ω cm² at 700 °C, which is only 1.8% of that for a pure LSM electrode, 5.6% of that reported for LSM–YSZ composites, and 13.2% of that for reported LSM–GDC (gadolinia-doped ceria) electrodes, demonstrating that YSB is very effective to enhance the performance of LSM-based cathodes. The electrode performance is also affected by the electrolyte substrate. LSM electrodes without any YSB exhibit obviously different performance on YSZ, SDC and YSB electrolytes. However, when YSB is cooperated, R_p on different electrolytes tends to become equivalent, especially for electrodes with high YSB content. Further analysis shows that their electrochemical performance is contributed dominantly from the electrode bulk whereas the contribution from the electrode/electrolyte interface is negligible, suggesting weak electrolyte effect on the performance of LSM–YSB composite electrodes.     

Nanoconfined 2LiBH4–MgH2–TiCl3 in carbon aerogel scaffold for reversible hydrogen storage

Nanoconfinement of 2LiBH₄–MgH₂–TiCl₃ in resorcinol–formaldehyde carbon aerogel scaffold (RF–CAS) for reversible hydrogen storage applications is proposed. RF–CAS is encapsulated with approximately 1.6 wt. % TiCl₃ by solution impregnation technique, and it is further nanoconfined with bulk 2LiBH₄–MgH₂ via melt infiltration. Faster dehydrogenation kinetics is obtained after TiCl₃ impregnation, for example, nanoconfined 2LiBH₄–MgH₂–TiCl₃ requires ∼1 and 4.5 h, respectively, to release 95% of the total hydrogen content during the 1st and 2nd cycles, while nanoconfined 2LiBH₄–MgH₂ (∼2.5 and 7 h, respectively) and bulk material (∼23 and 22 h, respectively) take considerably longer. Moreover, 95–98.6% of the theoretical H₂ storage capacity (3.6–3.75 wt. % H₂) is reproduced after four hydrogen release and uptake cycles of the nanoconfined 2LiBH₄–MgH₂–TiCl₃. The reversibility of this hydrogen storage material is confirmed by the formation of LiBH₄ and MgH₂ after rehydrogenation using FTIR and SR-PXD techniques, respectively.