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Abstract Economically harvesting energy from a microbial fuel cell (MFC), increasing its electrical power production, and developing its role as a practical energy supply, needs a low-cost and high-performance design of the MFC compartments. According to this strategy, a novel monolithic membrane electrode assembly (MEA) was fabricated and evaluated as an air–cathode in a single-chamber MFC (SCMFC). The MEA was made of bacterial cellulose (BC), conductive multi-walled carbon nanotubes (CNT), and nano-zycosil (NZ). BC, as a nano-celluloses with oxygen barrier property, can maintain anaerobic conditions for the anode compartment. Binder-less CNT coating on BC avoids costly binders such as poly-tetra fluoro ethylene (PTFE) and Nafion and decreases the MEA charge transfer resistance. NZ, as a very cheap modifier, not only prevents the anolyte leakage but also provides more MEA’s active sites for the oxygen reduction reaction (ORR). The electrochemical performance of the MEA was compared to a PTFE- based gas diffusion electrode (GDE) in the SCMFC. The MEA cell provided a pulse power density of 1790 mW/m2, roughly twice as high as the pulse power density of GDE (920 mW/m2). SCMFC’s internal resistance decreased from 1.84 KΩ (with GDE) to 0.8 KΩ (with MEA). Also, the cell’s columbic efficiency increased from 4.2% (with GDE) to11.7% (with MEA). Additionally, the capacitance of the MEA (65 mF) was much higher than the value for GDE (0.73 mF). Thus, the MEA compared to the GDE showed higher performance in the SCMFC for electricity generation and wastewater treatment at a lower cost.

AbstractAn analysis of Italy's National Energy Budget of in the last decades shows the important role of the civil sector and the impact of fossil fuels in air conditioning systems. The high consumption of fossil fuel is Likely due to the predominance of plants with conventional boilers in buildings. Based on the analysis of the Exergy flow this paper proposes the Cogeneration technology for Air conditioning systems with heat pumps to implement the Rational Use of Energy. The feasibility of a retrofit intervention on existing systems of a large size is shown, by the projection of a cogeneration plant for the buildings of the University of Cagliari currently equipped with fossil fuel plants.

AbstractThe penetration of renewable sources, particularly wind and solar, into the grid has been increasing in recent years. As a consequence, there have been serious concerns over reliable and safety operation of power systems. One possible solution, to improve grid stability, is to integrate energy storage devices into power system network: storing energy produced in periods of low demand to later use, ensuring full exploitation of intermittent available sources. Focusing on stand-alone photovoltaic (PV) energy system, energy storage is needed with the purpose of ensuring continuous power flow, to minimize or, if anything, to neglect electrical grid supply.A comprehensive study on a hybrid stand-alone photovoltaic power system using two different energy storage technologies has been performed. This study examines the feasibility of replacing electricity provided by the grid with hybrid system to meet household demand. This paper is a part of an experimental and a theoretical study which is currently under development at University of Bologna. A test facility is under construction, at the University of Bologna, for the experimental characterization of the cogenerative performance of small scale hybrid power systems, composed of micro-CHP systems of different technologies : a Micro Rankine Cycles (MRC), a Proton Exchange Membrane Fuel Cells (PEM-FC), a battery, an electrolyzer and a heat recovery subsystem. The test set-up is also integrated with an external load simulator, in order to generate variable load profiles.This paper presents the theoretical results of the performance simulations developed considering an hybrid system consisting on a photovoltaic array (PV), electrochemical batteries (B) and electrolyzer (HY) with a H2 tank and a Proton Exchange Membrane Fuel Cell (PEM-FC) stack, in case of a household electrical demand. The performance of this system have been evaluated by the use of a calculation code, in-house developed by University of Bologna; future activities will be the tuning of the software with the experimental results, in order to realize a code able to define the correct size of each sub-system, ones the load profile of the utility is known or estimated.

AbstractAlthough the application of internal insulation to existing perimeter walls poses significant challenges in terms of building physics and loss of habitable space, it is sometimes an inevitable choice because of practical or legislative constraints. Innovative solutions are then required to deliver satisfying performances and reduce nuisance to inhabitants of residential buildings in case they are going to remain in their flats during the retrofit works.Three systems for inner thermal retrofitting purposes have been designed and produced as prototypes. Two of them are composed by silica aerogel containing fibrous material: the first one is a rigid flat laminated panel, the second one is a rollable solution with a fabric finishing layer. The third insulating system is a perlite based board with a hydrophobic layer. All the materials composing the retrofit solutions have been characterized by means of laboratory tests in order to measure their main hygrothermal properties. In fact, some parameters are fundamental for determining the hygrothermal performance of the composite systems: thermal conductivity, at dry and wet state (moisture dependant), water vapour diffusion resistance factor, hygroscopic sorption at isotherm condition and water absorption coefficient. All those measured data were necessary for optimizing the solutions, guaranteeing energy efficiency and vapour open layers to systems that are intended for installation on existing walls.

The increasing demand for energy and commodities has led to escalating greenhouse gas emissions, the chief of which is represented by carbon dioxide (CO2). Blue hydrogen (H2), a low-carbon hydrogen produced from natural gas with carbon capture technologies applied, has been suggested as a possible alternative to fossil fuels in processes with hard-to-abate emission sources, including refining, chemical, petrochemical and transport sectors. Due to the recent international directives aimed to combat climate change, even existing hydrogen plants should be retrofitted with carbon capture units. To optimize the process economics of such retrofit, it has been proposed to remove CO2 from the pressure swing adsorption (PSA) tail gas to exploit the relatively high CO2 concentration. This study aimed to design and numerically investigate a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the PSA tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant using NaX zeolite adsorbent. The effect of operating conditions, such as purge-to-feed ratio and desorption pressure, were evaluated in relation to CO2 purity, CO2 recovery, bed productivity and specific energy consumption. We found that conventional cycle configurations, namely a 2-bed, 4-step Skarstrom cycle and a 2-bed, 6-step modified Skarstrom cycle with pressure equalization, were able to concentrate CO2 to a purity greater than 95% with a CO2 recovery of around 77% and 90%, respectively. Therefore, the latter configuration could serve as an efficient process to decarbonize existing hydrogen plants and produce blue H2.

A novel free-standing and flexible counter electrode for dye solar cells has been developed by conveniently transferring a vertically aligned carbon nanotube forest onto an oxygen-plasma-treated flexible, free-standing and conductive nanocomposite foil. Vertically aligned carbon nanotubes were first grown onto an aluminium foil by chemical vapour deposition and then transferred to the nanocomposite surface by hot pressing. The most meaningful electrochemical parameters have been quantitatively analyzed by means of electrochemical impedance spectroscopy and cyclic voltammetry in order to elucidate how the implementation of the anisotropic carbon nanotube top layer impacts the ultimate catalytic performances of the plate. Such an engineered counter electrode is able to guarantee a fast and effective reduction of the iodide-based electrolyte as well as to provide a solar conversion efficiency that is comparable with a typical Pt/TCO-coated rigid counter electrode. A photocurrent density higher than 13.36 mA cm−2 along with a solar conversion efficiency of 7.26% have been reported for the dye solar cell mounting a counter-electrode based on vertically aligned carbon nanotubes implanted onto a conductive nanocomposite plate.

The combination of photonics and silicon technology is a great challenge because of the potentiality of coupling electronics and optical functions on a single chip. Silicon nanocrystals are promising in various areas of photonics especially for light-emitting functionality and for photovoltaic cells. This review describes the recent achievements and remaining challenges of Si photonics with emphasis on the perspectives of Si nanoscale materials. Many of the results and properties can be simulated and understood based on theoretical studies. However, some of the key questions like the light-emitting mechanism are subjects of intense debates despite a remarkable progress in the recent years. Even more complex and important is to move the known experimental observations towards practical applications. The demonstrated devices and approaches are often too complex and/or have too low efficiency. However, the challenge to combine optical and electrical functions on a chip is very strong, and we expect more research activity in the field of Si nanophotonics in the future.

Abstract This paper presents an original model capable of simulating the thermal behavior of a vanadium redox flow battery stack in standby condition, i.e. without power and reactant flow, where the temperature distribution in the cells evolves because of ions crossover through the membrane, Joule losses due to shunt currents and inherent self-discharge effects. For the first time, a model is presented that is capable of simulating the cell temperature distribution in the stack and its time evolution considering all above effects. The model is applied to a 9 kW/40-cell stack and validated against measurements from a thermal imager. Numerical results show that shunt currents affect the temperature in the stack and can be responsible for local increases of cell temperatures up to 10 °C if the solutions are initially at high state of charge. This effect can be critical if standby occurs after a period of operation, with the electrolyte stack temperature markedly higher than air temperature. In addition, results show that shunt currents can play a major role in the thermal behavior of compact stacks, based on new materials capable of high power density and low ion crossover. The model presented here can constitute the basis for advanced cooling strategies.