Michael R. Hibbs

Polysulfone and polyacrylate-based zwitterionic coatings for the prevention and easy removal of marine biofouling

A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1–2 µm) relative to commercial coating standards (>200 µm).

New multi-electron high capacity anodes based on nanoparticle vanadium phosphides

Nanoscale vanadium phosphides can serve as new high capacity anodes in alkaline aqueous electrolytes. Competing corrosion reaction(s) are mitigated with the novel use of an anion exchange membrane providing for capacities as high as 2800 mAh g(-1) @ 100 mA g(-1) discharge rate.

Ion transport within random-sulfonated and block-sulfonated copolyimides

A series of sulfonated copolyimides was prepared from 4,4-oxydianiline, sulfonated 4,4′-oxydianiline, and 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride). Both random- and block structures were prepared by varying the timing of monomer addition to the polymerization reaction. The polymers were converted to their acid forms and then cast into films. 1H NMR, FTIR, and non-aqueous titration verified the degree of polymer sulfonation. The block copolymers showed higher water uptake and proton conductivities than random copolymers with similar ion exchange capacity (IEC) values. These differences became pronounced as the IEC value was increased.

Characterizing fire danger from low-power photovoltaic arc-faults

While arc-faults are rare in photovoltaic installations, more than a dozen documented arc-faults have led to fires and resulted in significant damage to the PV system and surrounding structures. In the United States, National Electrical Code® (NEC) 690.11 requires a listed arc fault protection device on new PV systems. In order to list new arc-fault circuit interrupters (AFCIs), Underwriters Laboratories created the certification outline of investigation UL 1699B. The outline only requires AFCI devices to be tested at arc powers between 300-900 W; however, arcs of much less power are capable of creating fires in PV systems. In this work we investigate the characteristics of low power (100-300 W) arc-faults to determine the potential for fires, appropriate AFCI trip times, and the characteristics of the pyrolyzation process. This analysis was performed with experimental tests of arc-faults in close proximity to three polymer materials common in PV systems, e.g., polycarbonate, PET, and nylon 6,6. Two polymer geometries were tested to vary the presence of oxygen in the DC arc plasma. The samples were also exposed to arcs generated with different material geometries, arc power levels, and discharge times to identify ignition times. To better understand the burn characteristics of different polymers in PV systems, thermal decomposition of the sheath materials was performed using infrared spectra analysis. Overall a trip time of less than 2 seconds is recommended for the suppression of fire ignition during arc-fault events.

Non-platinum Carbon-Supported Oxygen Reduction Catalyst Ink Evaluation Based on Poly(sulfone) and Poly(phenylene)-Derived Ionomers in Alkaline Media

Described in this work is an electrochemical evaluation of novel alkaline ionomers employed as catalyst binder for non-platinum group metal electrocatalysts based on cyanamide precursor. Electrochemical evaluation of the non-platinum group metal (non-PGM) catalyst bound with the featured alkaline ionomer classes over a range of conditions gives insight into how they behave, as well as provide information on how the varying functionalities enhance or inhibit the rate of oxygen reduction. We are showing that the polymer backbone structure has a larger influence on facilitating favorable reaction kinetics than ionomer to catalysts ratio. The poly(sulfone)-derived ionomers result in a worse activity than electrocatalysts with Nafion® and poly(phenylene)-derived ionomers. They also exhibited more peroxide desorption and greater limitation in the mass transport regime. The poly(phenylene)-derived polymers performed in line with the benchmark ionomer, Nafion®. The poly(phenylene)-derived ionomers show promise as fruitful line of research in establishing an anion-conducting ionomer for alkaline electrolyte fuel cells.