Multilayer mirrors that maintain or increase their reflectivity with increasing incidence angle can be constructed using polymers that exhibit large birefringence in their indices of refraction. The most important feature of these multilayer interference stacks is the index difference in the thickness direction (z axis) relative to the in-plane directions of the film. This z-axis refractive index difference provides a variable that determines the existence and value of the Brewster's angle at layer interfaces, and it controls both the interfacial Fresnel reflection coefficient and the phase relations that determine the optics of multilayer stacks. These films can yield optical results that are difficult or impossible to achieve with conventional multilayer optical designs. The materials and processes necessary to fabricate such films are amenable to large-scale manufacturing.

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Solar conversion efficiencies for splitting water with semiconducting photoelectrodes are calculated from basic thermodynamic principles combined with transport properties matching those of the best materials presently available. Assuming no further constraints, we derive in this way “upper limit” estimates of efficiencies achievable via semiconductor photoelectrochemical cells (PEC's), operating with no external electrical bias. Both one‐ and two‐photon configurations are considered. A one‐photon PEC is found to have an “upper limit” efficiency of ∼7% (AM 1.2 solar energy to chemical potential energy stored as H2 ). For two‐photon configurations, the “upper limit” for a p‐n PEC is ∼10%, while for a tandem PEC it is ∼18%. The tandem cell configuration is the least sensitive to the choice of materials parameters and transport losses and yields the highest efficiencies. Significant increases in conversion efficiencies result from assuming lower oxygen overpotentials and higher photoelectrode fill factors than have been achieved so far, with the latter being the more important, however.

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The electro-oxidation of formic acid was studied in a direct-oxidation polymer-electrolyte fuel cell at 170°C using real-time mass spectrometry. The results are compared with those obtained for methanol oxidation under the same conditions. Formic acid was electrochemically more active than methanol on both Pt-black and Pt/Ru catalysts. The polarization potential of formic acid oxidation was ca. 90 to 100 mV lower than that of methanol.The oxidation of formic acid was dependent on the water/formic acid mole ratio. The best anode performance was obtained using a water/formic acid mole ratio of -2. In addition, Pt/Ru catalyst was more active than Pt-black for formic acid oxidation. The mass spectrometric results showed that CO2 is the only reaction product of formic acid oxidation.The results are discussed in terms of possible formic acid oxidation mechanisms.

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Electrochemical reduction of oxygen has been studied in detail employing rotating disk and ring‐disk electrode techniques in aqueous KOH solutions of various concentrations at various temperatures. Analysis of voltammetric results recorded at the rotating disk electrode (RDE) indicates that there are two clearly defined Tafel regions of low (60 mV/decade) and high false(200∼300 normalmV/normaldecadefalse) Tafel slopes. In general, electrode kinetics improves and Tafel slopes of the low‐slope region decreases slightly as the basicity of the electrolyte solution increases. The rotating ring‐disk electrode (RRDE) results were analyzed according to a simple model for oxygen reduction, first proposed by Damjanovic et al. The model is in agreement with experimental results at lower concentrations of KOH . Rate constants for oxygen reduction directly to H2O and H2O2 , and for H2O2 to H2O were calculated at four different disk electrode potentials. The rate constant of direct reduction of oxygen to H2O increases with the overpotential, but the plots of rate constants for oxygen reduction to H2O2 and for H2O2 reduction vs. potential pass through a maximum at about 0.85V vs. DHE. All these rate constants are shown to be slightly dependent on temperature.

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