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• Silicon microchannels of 3.3 mm in diameter have been successfully coated with RhPd/CeO 2 catalyst. • The catalytic microreactor has proven suitable to generate H 2 from various fuels containing different functional groups, obtaining the best performance for 2-methoxyethanol. • Given the outstanding surface-area-to-volume ratio of the Si micromonolith, hydrogen productions normalized by microreactor volume at 923 K of 110 L N H 2 /(mL 2-methoxyethanol,liquid cm3Reactor) were obtained at contact times of only 5.7 ms. A functionalized silicon micromonolith of 7 mm in diameter and 210 μm-thick was evaluated for the production of hydrogen from the steam reforming (SR) of various fuels, containing different functional groups, such as ethanol, acetic acid, 2-propanol, acetone, and 2-methoxyethanol. The micromonolith consisted of 2 million regular channels of 3.3 μm in diameter, which were coated with a 100-nm RhPd/CeO 2 catalytic layer. The catalytic activity was tested at temperatures between 823 and 1023 K, using overstoichiometric steam-to-carbon ratios and operating at contact times between 0.005 and 0.009 s. The best performance was obtained for the 2-methoxyethanol SR tests, where 53% H 2 selectivity was recorded. A remarkable hydrogen production normalized by reactor volume of 110 L N H 2 ·mL 2-methoxyethanol, liquid −1 cm−3 Reactor was recorded, leading to comparable H 2 yields to those obtained with a conventional monolith coated with the same RhPd/CeO 2 catalyst, owing to the large contact area. After more than 80 h under reaction conditions, the micromonolith was characterized by SEM and TEM. SEM analyses showed that no channels were blocked due to carbon deposition nor detached CeO 2 layers were found. These results demonstrate the feasibility of using catalytic Si micromonoliths as microreformers to generate hydrogen from the SR of different fuels to power portable fuel cells. [ABSTRACT FROM AUTHOR]

Selective thermal emitters concentrate most of their spontaneous emission in a spectral band much narrower than a blackbody. When used in a thermophovoltaic energy conversion system, they become key elements defining both its overall system efficiency and output power. Selective emitters׳ radiation spectra must be designed to match their accompanying photocell׳s band gap and simultaneously, withstand high temperatures (above 1000 K) for long operation times. The advent of nanophotonics has allowed the engineering of very selective emitters and absorbers; however, thermal stability remains a challenge since nanostructures become unstable at temperatures much below the melting point of the used materials. In this paper we explore a hybrid 3D dielectric–metallic structure that combines the higher thermal stability of a monocrystalline 3D silicon scaffold with the optical properties of a thin platinum film conformally deposited on top. We show experimentally that these structures exhibit a selective emission spectrum suitable for TPV applications and that they are thermally stable at temperatures up to 1100 K. These structures are ideal in combination with III–V semiconductors in the range E g =0.4–0.55 eV such as InGaAsSb ( E g =0.5–0.6 eV) and InAsSbP ( E g =0.3–0.55 eV). [ABSTRACT FROM AUTHOR]

Abstract: The present contribution reports the design, manufacture and experimental proof of concept of an ethanol micro-reformer for portable-fuel cell feeding. Through photo-assisted electrochemical etching, a silicon micromonolithic substrate with perfectly parallel cylindrical channels of 3.3 μm diameter was achieved (density of channels of ca. 4 × 104 channels mm−2). The channel walls were coated with a cobalt-based catalyst. The resultant functionalized micromonoliths were implemented in a stainless steel microreactor including feed evaporation facilities and electrical heating. The unit was successfully tested for ethanol steam reforming under non-diluted feed conditions at 773 K, achieving high hydrogen specific production rates, high ethanol conversions (>80%) and adequate selectivity profiles, with H2:CO2 molar ratios of ∼3 and low CO outlet concentrations. A performance comparison was performed with two other reforming substrates with the same catalyst formulation, namely, a conventional cordierite monolith and a conventional stainless steel microreactor. Results show for the Si-micromonolithic reactor a remarkable improvement of the specific hydrogen production rate (per unit reactor volume and feed flowrate), operating at considerably reduced residence times, due to the increase in contact area per unit volume. [Copyright &y& Elsevier]

Abstract: We address the need to develop efficient algorithms for numerical simulation of models, based in part or entirely on adaptive resonance theory. We introduce modifications that speed up the computation of the gated dipole field (GDF) in the Exact ART neural network. The speed increase of our solution amounts to at least an order of magnitude for fields with more than 100 gated dipoles. We adopt a ‘divide and rule’ approach towards the original GDF differential equations by grouping them into three categories, and modify each category in a separate way. We decouple the slow-dynamics part — the neurotransmitters from the rest of system, solve their equations analytically, and adapt the solution to the remaining fast-dynamics processes. Part of the node activations are integrated by an unsophisticated numerical procedure switched on and off according to rules. The remaining activations are calculated at equilibrium. We implement this logic in a Generalized Net (GN) — a tool for parallel processes simulation which enables a fresh look at developing efficient models. Our software implementation of generalized nets appears to add little computational overhead. [Copyright &y& Elsevier]