Michael K. Carpenter

Solvothermal Synthesis of Platinum Alloy Nanoparticles for Oxygen Reduction Electrocatalysis

Platinum alloy nanoparticles show great promise as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes. We report here on the use of N,N-dimethylformamide (DMF) as both solvent and reductant in the solvothermal synthesis of Pt alloy nanoparticles (NPs), with a particular focus on Pt-Ni alloys. Well-faceted alloy nanocrystals were generated with this method, including predominantly cubic and cuboctahedral nanocrystals of Pt(3)Ni, and octahedral and truncated octahedral nanocrystals of PtNi. X-ray diffraction (XRD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), coupled with energy dispersive spectroscopy (EDS), were used to characterize crystallite morphology and composition. ORR activities of the alloy nanoparticles were measured with a rotating disk electrode (RDE) technique. While some Pt(3)Ni alloy nanoparticle catalysts showed specific activities greater than 1000 μA/cm(2)(Pt), alloy catalysts prepared with a nominal composition of PtNi displayed activities close to 3000 μA/cm(2)(Pt), or almost 15 times that of a state-of-the-art Pt/carbon catalyst. XRD and EDS confirmed the presence of two NP compositions in this catalyst. HAADF-STEM examination of the PtNi nanoparticle catalyst after RDE testing revealed the development of hollows in a number of the nanoparticles due to nickel dissolution. Continued voltage cycling caused further nickel dissolution and void formation, but significant activity remained even after 20,000 cycles.

The electrochromic properties of hydrous nickel oxide

The electrochromic properties of thin films of nickel hydroxide on conductive tin-oxide-coated glass substrates are reported. Adherent, uniform thin films (⩽ 100 nm) which are cathodically electrodeposited from Ni(NO3)2 solution, can be repeatedly colored and bleached electrochemically in a 1M KOH electrolyte. In the reduced form, the films are essentially transparent, but upon oxidation they absorb light strongly throughout the visible region of the spectrum. Peak coloration efficiency, which occurs at about 450 nm, is estimated to be 50 cm2/C. Variable control of transmittance through the films was achieved by controlling the extent of film oxidation. Intrinsic switching times for coloration and bleaching are each less than one second. Nonuniform coloration and bleaching, due to the resistivity of the conductive glass substrate, increases the effective switching time as the electrode area is increased. The open circuit memory of colored films is on the order of hours in 1M KOH. Increased switching times and a decrease in total coloration are observed after 500 color/bleach cycles.

A Mathematical Model of the Oxygen‐Recombination Lead‐Acid Cell

A one-dimensional mathematical model of the oxygen-recombination lead-acid cell is developed. The model is applied to investigate mechanisms associated with oxygen recombination and species transport during charge. The conditions for rapid transport rates of gaseous oxygen through the separator and dissolved oxygen through the liquid film within the Pb electrodes are considered, and these rates are rapid for the conditions investigated. Model predictions show that during charge gas volume increases in the Pb electrode and decreases in the PbO{sub 2} electrode. At the onset of oxygen recombination during constant-current charge, the polarization of the Pb electrode is reduced, which results in the prediction of a maximum in cell voltage. This voltage behavior is demonstrated experimentally. The prediction of a voltage maximum by the mathematical model occurs when the recombination mechanism is the direct electrochemical reduction of oxygen at the Pb electrode. Model simulation with another recombination mechanism in which oxygen reacts chemically with lead to form lead sulfate does not produce a voltage maximum. A decrease in the amount of gas space surrounding the cell results in predictions of increased Pb-electrode depolarization.

Photoelectrochemistry of Nickel Hydroxide Thin Films

Semiconducteur type p. Etude du comportement photoelectrochimique des oxydes de nickel dans une solution alcaline

ELECTROCHEMICAL CODEPOSITION OF INDIUM AND ANTIMONY FROM A CHLOROINDATE MOLTEN SALT

The electrochemical codeposition of In and Sb from a novel low temperature molten salt electrolyte is reported. The melt, which consists of InCl 3 and 1-methyl-3-ethylimidazolium chloride, allows the codeposition to be accomplished at 45 °C. XPS shows that InSb can be deposited from this system. Electrochemical experiments are provided along with an interpretation that draws on the importance of In(I) species in the melt.

LUMINESCENT PHOTOELECTROCHEMICAL CELLS - 7. PHOTOLUMINESCENT AND ELECTROLUMINESCENT PROPERTIES OF CADMIUM SULFO-SELENIDE ELECTRODES.

Photoelectrochemical cells (PECs) are being widely studied as devices for optical energy conversion. The excited-state properties of the semiconductors around which PECs are constructed are crucial to efficient energy conversion. We have employed luminescence as a probe of these excited-state-properties, generally using materials such as n-type CdS:Te(Te-doped CdS) which exhibit subband gap emission. Recently we examined emission of band gap energy from n-type CdS and CdSe, two materials which have been used extensively in PEC studies. Since these two compounds form solid solutions over the entire composition range, the mixed compounds represent a natural extension of our emissive studies. We report herein that luminescence from samples of n-type, single-crystal CdSXSe1-X can be used to probe interfacial charge-transfer events relevant to PECs. Specifically, we demonstrate that photoluminescence (PL) can be perturbed and electroluminescence (EL) initiated by interfacial charge-transfer processes.

Anode Materials for Mitigating Hydrogen Starvation Effects in PEM Fuel Cells

Localized hydrogen starvation at a polymer electrolyte membrane (PEM) fuel cell anode can lead to the formation of local cells in the membrane electrode assembly, which cause performance degradation at the fuel cell cathode due to carbon corrosion. We propose using hydrogen spillover materials as a hydrogen reservoir in the fuel cell anode in order to compensate for any temporary proton deficit caused by local flooding of the anode channels. We tested composite electrodes containing TiO 2 , WSi 2 , and WO 3 , and compared their behavior to that of commercial Pt/Vulcan XC-72 carbon (Pt/Vu) benchmark catalysts, using gas-diffusion electrodes in a 0.1 M HClO 4 solution and pellet electrodes in a 0.5 M H 2 SO 4 solution. While TiO 2 yields no benefits, both WSi 2 and WO 3 can significantly delay the voltage excursion of the gas-diffusion electrode into the oxygen evolution region upon the cessation of hydrogen flow. X-ray data indicate that the beneficial effect of WSi 2 may be caused by WO 3 , because we observed conversion of WSi 2 to W0 3 during voltage cycling, without a significant loss in the apparent hydrogen adsorption―desorption area. Electrodes with WO 3 yielded the best results, with a hydrogen storage charge higher by a factor of 6 than for the Pt/Vu benchmark.

Electrolyte-free electrochromic device

A novel, solid‐state electrochromic device is described which utilizes a single film of Prussian blue as the only electrochemically active element. The device can be reversibly bleached by the application of a voltage across the film. Removal of the voltage results in immediate recoloration.