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Abstract:We report structural and optical properties of three-dimensional periodic metallic woodpile structures obtained by direct laser writing in dielectric photoresist SU-8 and subsequent electroless coating by a thin Ni film. Signatures of photonic stop gaps were observed in optical reflection spectra of the structures at infrared wavelengths. This study demonstrates that the combination of DLW and chemical infiltration of metals is attractive as a simple and cost-efficient method for the fabrication of metalo-dielectric photonic crystals.

Thermodynamic analysis of energy conversion from light-to-chemical, light-to-electric and electric-to-chemical is presented by the case study of water photoelectrolysis on TiO(2) surface. It is demonstrated that at the current state-of-the-art energy conversion efficiency of water photoelectrolysis can be increased approximately 17 times by separating the processes of solar-to-electric and electric-to-chemical energy conversion and optimizing them independently. This allows to mitigate a high overvoltage of oxygen evolution reaction with respect to thermodynamic E(0)(O(2)/H(2)O) = 1.23 V potential as well as spectrally narrow absorbtivity of solar light by TiO(2) which determine the low efficiency (approximately 1.0%) of direct light-to-chemical energy conversion. Numerical estimates are provided illustrating practical principles for optimization of the solar energy conversion and storage processes.

Iridium oxide films (IROFs) are known to have an enhanced or the so-called super-Nernstian (< 59 mV/pH) pHsensitivity. The intention in the present study was to find out the reasons of such behavior and also to elucidate the nature of iridium anodic oxidation processes. The methods employed were combined cyclic voltammetry and chronopotentiometry. Iridium layers of 0.1 to 0.2 mm thickness, deposited thermally on titanium or gold-plated titanium substrates, were used for investigations. IROFs on the surface of working electrodes were formed anodically by applying a constant potential in deaerated and oxygen-containing solutions of 0.5 M H 2 SO 4 , 0.1 M KOH and 0.5 M H 3 PO 4 þ KOH. Linear pH-dependences of the stationary open-circuit potential with the slopes close to 59 mV/pH were found for iridium electrode oxidized at 0.4 V -0.8 V (RHE) in deaerated and at 0.8 V -1.2 V (RHE) in O 2 -containing solutions. They were attributed to reversible Ir/Ir(OH) 3 and Ir/ IrO 2 · nH 2 O metal-oxide electrodes, respectively. It has been suggested that the main current peaks seen in the voltammograms of iridium electrode in acid and alkaline solutions are of different nature. The difference between iridium electrode surface states in acid and alkaline solutions has been presumed to be the main reason of super-Nernstian pH-sensitivity of the IROFs. On the basis of the results obtained standard potential of Ir/Ir(OH) 3 electrode and the solubility product of Ir(OH) 3 have been evaluated: E Ir=IrðOHÞ 3 ¼ 0.78 AE 0.02 V and K sp ¼ 3.3 Â 10 À64 .