Philippe Stevens

Solid polymer electrolyte water electrolysis: electrocatalysis and long-term stability

Abstract In order to enhance the performance and long-term stability of a water electrolysis pilot plant, IrO 2 /Ti electrodes were hot-pressed on both sides of a Nafion® membrane and tested. By comparison with Pt electrodes, we obtained much lower anodic overvoltages and a better long-term stability of the cell voltage due to a lower cathode sensitivity to poisoning. Purification of water using ion-exchange resins was also useful to prevent a poisoning of the membrane itself. In purified water, assemblies using Pt cathodes and IrO 2 anodes were found to be a good compromise between performance and stability.

Development of a Rechargeable Zinc-Air Battery

Zinc air batteries have very high theoretical energy densities (> 900 Wh/kg) and are made of cheap abundant materials (zinc, potassium hydroxide, carbon, manganese). The cost of zinc is close to 1 €/kWh based on current zinc prices (around 1000 €/tonne) and the air electrode can be made for as little as 18

Development of a Lithium Air Rechargeable Battery

/m2 for the equivalent of 500 000 vehicles/year, which adds around between 4-5 €/kWh to the cost of the battery. Zinc-air batteries could potentially be manufactured at a cost lower than lead-acid batteries, the cheapest technology today. World resources of zinc are estimated at 300 times greater than those of lithium and therefore pose no threat of resource limitation, even if all vehicles were powered with zinc. The zinc-air battery is an aqueous system with no toxic or inflammable substances. Zinc is also easily recyclable. They are therefore safe and environmentally friendly. Commercial primary button cell zinc-air batteries are sold by the millions everyday for hearingaids. They can have very high energy densities, up to 442 Wh/kg for the Duracell DA675 button cell. The primary zinc-air battery is therefore a mature technology, which is not the case for the secondary, rechargeable variety. All these properties therefore make them very good candidates for electric vehicles. Unfortunately, their major drawback is the very low lifetime of the battery when recharged electrically.

Far infrared electrochromism in unique conducting polymer systems

Rechargeable aqueous lithium-air cells have been developed and manufactured with the objective of analysing the limitations of the technology. The barriers to the technology have been identified and solutions to some of them have been successfully demonstrated in this study.

New electrodes for hydrogen/oxygen solid polymer electrolyte fuel cell

We report herein the first significant infrared (IR) electrochromism in Conducting Polymers (CPs), to our knowledge, with applications in battlefield countermeasures against night vision devices, and thermal control panels for spacecraft. Thin (< 2 mm), flexible, variable area (1 cm 2 to 1 m 2 ), entirely solid state, CP flat panels were developed, showing: high Reflectance variation, e.g. 15% to 68% at 10.5 microns, 45% to 73% at 16.5 microns, and 31% to 77% at 620 nm; switching times of < 1 sec; cyclabilities of 10 5 cycles; For spacecraft application: Gier-Dunkle measurements showed Emittance variations from 0.32 to 0.79, Solar Absorptance 0.39 to 0.79; operating temperatures -35 to + 85 C; ability to withstand gamma radiation to 7.6 MRad, vacuum to 10 -7 torr. Poly(aniline) with a polymeric-matrix dopant was the primary CP used. Recent issuance of our primary US patents permit disclosure of these data and discussion of the unique device design.

New chemical process for the preparation of fine powders and thin films of LSMx-YSZ composite oxides

Abstract A new method of preparation of Electrode/Membrane/Electrode (EME) assemblies for Proton Exchange Membrane Fuel Cells (PEMFC) has been developed. The electrodes are deposited directly onto a NAFION ® electrolyte membrane from a mixture of platinized carbon. NAFION ® solution, and PTFE by using a spray technique. By this technique, porous electrodes are obtained with an optimized gas/electrolyte/catalyst interface and electrode/membrane interface.

The effect of zirconium (IV) oxide on the electrocatalytic activity of carbon supported Pt/Ru porous electrodes for the electrochemical oxidation of methanol in acid electrolyte.

Abstract Composite cathodes of La1−xSrxMnO3-yttria stabilized zirconia with various molar concentrations were deposited onto dense YSZ electrolytes by dip-coating technique. The dip-coated solution is original and is based on polymeric solution. Different ways were examined to prepare it. Pure composites are only obtained when the final polymeric solution is an emulsion between two intermediate polymeric solutions: in one solution, Laue5f8Srue5f8Mn cations are present while the other one contains Yue5f8Zr cations. The cathode characteristics were then examined by scanning electron microscopy (SEM). Crack-free and homogeneous films are obtained. The porosity and the thickness of the film are a function of the molar ratio of YSZ in the composite film. Films with a porosity of about 30% are synthesized.

Effect of Lithium and Potassium Cations on the Electrocatalytic Properties of Carbon and Manganese Oxide Electrocatalysts Towards the Oxygen Reduction Reaction in Concentrated Alkaline Electrolyte

Abstract The use of metal oxides as promoters in the electrooxidation of methanol in acid electrolyte on carbon supported platinum electrodes has been investigated. The addition of zirconium(IV) oxide to carbon supported Pt/Ru electrodes as a third co-promoter and its effect on the electrode activity was studied by varying the Pt:Ru:Zr ratio using a full factorial design and analysed using a Yates statistical analysis.

Hybrid Li Ion Conducting Membrane as Protection for the Li Anode in an Aqueous Li–Air Battery: Coupling Sol–Gel Chemistry and Electrospinning

The impact of alkaline cations (Li+ and K+) on the electrocatalytic properties of high-surface-area carbon (HSAC) and nanometric manganese oxides (MnOx) deposited onto HSAC (MnOx/C) used as oxygen reduction reaction (ORR) electrodes has been studied in concentrated LiOH or KOH media. The electrochemical characterizations firstly reveal that HSAC have good ORR electrocatalytic properties in these strong alkaline electrolytes, in agreement with the literature. However, although MnOx/C exhibits high ORR activity in NaOH and KOH media below 1xa0M (Roche et al., J Phys Chem C 111:1434, 2007), the present study reveals their deactivation in concentrated LiOH or KOH electrolytes because of an insufficient activity of water. The latter is indeed not compatible with a sufficient presence of protons in solution, thereby limiting the necessary proton insertion into the MnOx lattice, a prerequisite for ORR activity (Roche et al., J Phys Chem C 111:1434, 2007). In addition, when LiOH electrolyte is used, another effect penalizes the electrode performances; Li+ ions may insert into the MnOx lattice and stabilize both the Mn atoms at the oxidation state 3 and the oxygen groups at the carbon surface, which prevents their role of redox mediating species and further blocks the catalytic process, eventually yielding increased ORR overpotential.

Electrical Interaction Model of Planar SOFC Stack Fed with Natural Gas

Aqueous lithium-air batteries have very high theoretical energy densities, which potentially makes this technology very interesting for energy storage in electric mobility applications. However, the aqueous electrolyte requires the use of a watertight layer to protect the lithium metal, typically a thick NASICON glass-ceramic layer, which adds ohmic resistance and penalizes performance. This article deals with the replacement of this ceramic electrolyte by a hybrid organic-inorganic membrane. This new membrane combines an ionically conducting inorganic phase for Li ion transport (Li1.3Al0.3Ti1.7(PO4)3 (LATP) and a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer for water tightness and mechanical properties. The Li ion transport through the membrane is ensured by an interconnected 3-D network of crystalline LATP fibers obtained by coupling an electrospinning process with the sol-gel synthesis followed by thermal treatment. After an impregnation step with PVDF-HFP, hybrid membranes with different volumetric fractions of PVDF-HFP were synthesized. These membranes are watertight and have Li ion conductivities ranging from 10-5 to 10-4 mS/cm. The conductivity depends on the PVDF-HFP volume fraction and the fibers alignment in the membrane thickness, which in turn can be tuned by adjusting the water content in the electrospinning chamber during the process. The alignment of fibers parallel to the membrane surface is conductive to poor conductivity values whereas a disordered fiber mat leads to interesting conductivity values (1 × 10-4 mS/cm) at ambient temperature.