E. Bradley Easton

Properties of Gas Diffusion Electrodes Containing Sulfonated Poly(ether ether ketone)

The use of sulfonated poly(ether ether ketone) as the proton-conducting medium within the electrocatalytic layer of fuel cell gas diffusion electrodes (GDEs) is described. An electrochemically active surface area determined by cyclic voltammetry and electrochemical impedance spectroscopy was studied as a function of ion exchange capacity. Maximum activity is related to the concentration of sulfonate groups within the catalyst layer. Despite their relatively high electrochemical surface area and catalyst utilization, fuel cell performance is rather poor compared to Nafion-based GDEs. Fuel cell performance is greatly enhanced when polytetrafluoroethylene (PTFE) is incorporated into the catalyst layer. The addition of PTFE results in GDEs with larger pore diameters that are less prone to flooding. The incorporation of an ionomer of similar chemical structure to the proton-conducting membrane employed is shown to reduce interfacial resistance. Electrode structures of this type may prove useful for investigating other novel proton-conducting materials.

Co – C – N Oxygen Reduction Catalysts Prepared by Combinatorial Magnetron Sputter Deposition

Thin-film libraries of CO x C 1-x-y N y . (0 < x < 0.107, 0.003 < y < 0.389) were prepared by combinatorial magnetron sputter deposition in an Ar/N 2 gas mixture followed by subsequent heat-treatment at 700, 800, or 1000°C in N 2 atmosphere. By increasing the nitrogen partial pressure during sputtering, the nitrogen content was increased significantly in the as-sputtered libraries and more nitrogen remained in the libraries after heat-treatment. The catalytic activities of the libraries towards the oxygen reduction reaction (ORR) were studied using the rotating ring-disk electrode (RRDE) technique. CO x C 1-x-y N y libraries heat-treated at 800°C with 0.004 < x < 0.105 and 0.026 < y < 0.097 showed good catalytic activities towards ORR in 0.1 M HClO 4 solution at room temperature. The heating temperature that induces the onset of catalytic activity coincides with the temperature at which both substantial nitrogen release from the originally amorphous films and the formation of graphitic carbon and β-Co occurs. This temperature varies significantly with both the Co and N content in the films. The production of H 2 O 2 and the corrosion stability of the libraries are also discussed.

Characteristics of Polypyrrole/Nafion Composite Membranes in a Direct Methanol Fuel Cell

Commercial perfluorosulphonic acid membranes (Nafion) have been impregnated with polypyrrole by in situ polymerization to decrease the crossover of methanol in direct methanol fuel cells (DMFCs). Modified membranes produced by polymerization of the pyrrole with hydrogen peroxide and iron(III) have been evaluated in a DMFC. Both methods produce membranes that can provide enhanced cell performance, although membranes produced with iron(III) as the oxidizing agent for the polymerization require additional treatments to restore their conductivity and promote bonding to the electrodes. Performance gains result from substantial reductions of the cathode overpotential, while anode overpotentials increase due to the lower conductivities of the modified membranes. Part of the beneficial effect at the cathode appears to be due to lower water crossover from the anode to the cathode.

Fe-C-N oxygen reduction catalysts prepared by combinatorial sputter deposition

Thin-film libraries of Fe x C 1-x-y N y libraries (0 < x < 0.12; 0 < y < 0.5) have been prepared by combinatorial sputter deposition. The libraries were subsequently annealed at 700, 800, and 1000°C to induce structural and compositional changes. Respectable catalytic activity was achieved with libraries having 0 < x < 0.035 and 0.01 < y < 0.16 that were annealed at 800°C. This is explained in terms of nitrogen content and the degree of graphitization of the annealed catalysts.

Thermal Evolution of the Structure and Activity of Magnetron-Sputtered TM–C–N ( TM = Fe , Co ) Oxygen Reduction Catalysts

Thin-film libraries of TM x C 1-x-y N x (TM = Fe, Co; 0 < x < 0.09; 0 < y < 0.5) have been prepared by combinatorial sputter deposition. The libraries were subsequently annealed at 700-1000°C to induce structural and compositional changes. Using grazing-incidence X-ray diffraction and scanning electron microscopy, structural changes were followed as a function of annealing temperature. At temperatures above 700°C, the previously homogeneous and amorphous thin films became a heterogeneous mixture of (partially) graphitized nitrogen-containing carbon and either Fe 3 C or β-Co. The onset of this transformation is accompanied by a rapid decrease in N content and occurs as a function of both transition metal content and temperature. Catalytic activity for oxygen reduction is at its maximum partway through this transformation.

Magnetron Sputtered Fe – C – N , Fe – C , and C – N Based Oxygen Reduction Electrocatalysts

Thin-film libraries of Fe x C 1-x-y N y (0 < x < 0.06, 0 < y < 0.5) have been prepared by combinatorial sputter deposition in a 40/60 N 2 /Ar process gas. The libraries were subsequently annealed between 800 and 1000°C to induce structural and compositional changes. These libraries contained/retained more nitrogen than those sputtered in lower N 2 partial pressures. Physical and electrochemical properties of these combinatorial libraries were studied using scanning electron microscopy, X-ray photoelectron spectroscopy, and rotating ring-disk electrode cells. Maximum catalytic activity for oxygen reduction reaction in acid was achieved for the libraries annealed at 800°C and approaches the best activity of Fe-C-N-based electrocatalysts reported in the literature to date.

Advanced NOx gas sensing based on novel hybrid organic–inorganic semiconducting nanomaterial formed between pyrrole and Dawson type polyoxoanion [P2Mo18O62]6−

Dawson-type K6P2Mo18O62·nH2O can be used as an oxidizing agent to polymerize pyrrole and yield a hybrid organic–inorganic nanostructured material [{Py}6(P2Mo18O62)]x. By adding the mild reducing agent potassium iodide (KI), the polymerization process was controlled to generate a hybrid material with low polypyrrole content [K4{Py}2(P2Mo18O62)]y. The electrical transport properties of [K4{Py}2(P2Mo18O62)]y displayed a perfect transistor operation suitable for gas sensing applications. Exposure of [K4{Py}2(P2Mo18O62)]y to various gases illustrated a selective and sensitive response to NOx gases. In addition, an interesting extended linearity up to 5500 ppm was recorded.

A Surface Modification Route to Nonprecious Metal Fuel Cell Catalysts

Nonprecious metal oxygen reduction reaction catalysts have been prepared via a simple chemisorption-based methodology. First, an aminosilane was chemically attached to a carbon surface, followed by coordination of iron and subsequent high temperature pyrolysis. Catalysts were prepared from a series of mono, di, and triaminosilanes. Physical and electrochemical properties of these catalysts were studied using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and rotating ring-disk electrode cells. Maximum catalytic activity was achieved for samples prepared from the triaminosilane combined with a more disordered carbon black.

Terpyridine-Based Monolayer Electrochromic Materials

Novel electrochromic (EC) materials were developed and formed by a two-step chemical deposition process. First, a self-assembled monolayer (SAM) of 2,2:6,2″-terpyridin-4-ylphosphonic acid, L, was deposited on the surface of a nanostructured conductive indium-tin oxide (ITO)xa0screen-printed support by simple submerging of the support into an aqueous solution of L. Further reaction of the SAM with Fe or Ru ions results in the formation of a monolayer of the redox-active metal complex covalently bound to the ITO support (Fe-L/ITO and Ru-L/ITO, respectively). These novel light-reflective EC materials demonstrate a high color difference, significant durability, and fast switching speed. The Fe-based material shows an excellent change of optical density and coloration efficiency. The results of thermogravimetric analysis suggest high thermal stability of the materials. Indeed, the EC characteristics do not change significantly after heating of Fe-L/ITO at 100 °C for 1 week, confirming the excellent stability and high EC reversibility. The proposed fabrication approach that utilizes interparticle porosity of the support and requires as low as a monolayer of EC active molecule benefits from the significant molecular economy when compared with traditional polymer-based EC devices and is significantly less time-consuming than layer-by-layer growth of coordination-based molecular assemblies.

The impact of pre-swelling on the conductivity and stability of Nafion/sulfonated silica composite membranes

Nafion/sulfonated silica composite membranes were prepared by modifying Nafion NRE 212 membranes with 2-(4-chlorosulfonylphenyl) trimethoxysilane in a one step process. Prior to modification, one set of membranes were pre-swollen in methanol, while another set were not. The resultant composite membranes were characterized for their water retention capabilities and proton conductivity at various relative humidity conditions. Composites prepared from pre-swelled Nafion membranes had higher sulfonated silica (SS) content than those prepared from non-swelled Nafion membranes. Despite this higher SS content, composites prepared from non-swelled Nafion displayed higher proton conductivity and water contents under low relative humidity conditions. Furthermore, composites prepared from pre-swollen membranes were less stable, having a high propensity to leach SS after long-term immersion in water as determined by TG, which will severely limit their lifetime in fuel cell applications.