• Energy Research

Micro power sources have a wide potential market for consumer electronics and portable applications, such as weather stations, medical devices, signal units, APU (auxiliary power units), gas sensors, and security cameras. A micro power source could be the direct methanol fuel cell system (DMFC). An important aspect of this system is the precise control of the concentration of the alcohol-water solution fed to the anode. Different detection principles were taken into consideration: electrochemical, infrared spectroscopy, gas chromatography, refractometry, density measurements, ultraviolet absorption. The present work is devoted to the study of an electrochemical amperometric sensor. The device is based on the electro-oxidation of methanol to carbon dioxide on platinum catalyst into a polymeric-membrane fuel cell operated as a galvanic cell. The alcohol-water solution under examination is fed to the anode (positive side) of a polymeric membrane fuel cell, where it reacts with water to produce carbon dioxide, protons, and electrons. Protons diffuse through the electrolyte material and recombine with electrons on the cathode catalyst (negative side). At high potentials (>0.7V) mass transfer of methanol to the electrode solution interface controls the observed current. Therefore, it is possible to correlate the solution concentration to the observed limiting current. This method was successfully applied to relatively diluted solutions (concentration <1M). The application of this principle to more concentrate solutions (up to 2M) requires an optimization of the anode structure to enhance the influence of mass transport limitation. Moreover, during continuous operation of the sensor, a decay of the signal was observed: the absence of a steady-state current value hinders the application of the sensor. An explanation of this phenomenon and a possible solution strategy are proposed.

Abstract The freeze-drying technique is employed for the production of novel strontium bromide/graphite/nanocellulose composites for thermochemical heat storage application. The aim is to obtain a better control and stability of salt organization within the composite, while maximizing the air/salt and salt/graphite interfacial areas and enhancing mass and heat transfer associated to the salt hydration and dehydration. A comparison with a conventional wet impregnation method is also reported. The morphology was investigated by means of scanning electron microscopy. Differential scanning calorimetry was employed to evaluate the energy storage density, while hydration kinetics were evaluated at 23 °C and 50% RH. The wet impregnation approach delivered materials with a limited porosity while freeze-drying produced highly porous structures with oriented channels for moisture transport across the composite. The organic binder provided an active contribution to the energy storage process, producing energy storage densities up to 764 kJ/kg, 48% greater than the theoretical value. Freeze-dried nanocellulose composites evidenced a significant increase of 54% in the hydration kinetics, compared to the pristine salt. Based on these results, the freeze-drying of ternary composites based on salt hydrate, graphite and nanocellulose is envisaged as a promising route for the production of fast charge and discharge thermochemical storage systems.

We describe a one-step detergent solubilization protocol for isolating a highly active form of Photosystem II (PSII) from Pisum sativum L. Detailed characterization of the preparation showed that the complex was a monomer having no light harvesting proteins attached. This core reaction centre complex had, however, a range of low molecular mass intrinsic proteins as well as the chlorophyll binding proteins CP43 and CP47 and the reaction centre proteins D1 and D2. Of particular note was the presence of a stoichiometric level of PsbW, a low molecular weight protein not present in PSII of cyanobacteria. Despite the high oxygen evolution rate, the core complex did not retain the PsbQ extrinsic protein although there was close to a full complement of PsbO and PsbR and partial level of PsbP. However, reconstitution of PsbP and PsbPQ was possible. The presence of PsbP in absence of LHCII and other chlorophyll a/b binding proteins confirms that LHCII proteins are not a strict requirement for the assembly of this extrinsic polypeptide to the PSII core in contrast with the conclusion of Caffarri et al. (2009).

The profitability of biodiesel is nowadays limited by the price of raw materials, which require high purity standards to be employed in conventional production processes. To overcome this problem, the transesterification of triglycerides in alcohol supercritical conditions could be conveniently used: the non-catalytic nature of this process allows the use of recycled raw materials, which are cheaper. To this end, a pilot scale plant for the continuous production of biodiesel in supercritical conditions was designed, manufactured and operated. In this research paper, rapeseed oil and bioethanol were used as raw materials, and the investigated temperatures were between 200 and 340°C, the pressure between 150 and 240 bar, and the alcohol-to-oil ratio ranged between 9 and 100. The best fatty acid ethyl ester (FAEE) yields were obtained at 340°C, 240 bar and a molar ratio of 42, which is line with easier-to-control lab-scale tests in batch conditions found in the literature. This encourages widening of the operating conditions to further improve the maximum achievable yields for the rapeseed oil-ethanol system.

Abstract A novel method is proposed for studying kinetics and overall activity of water oxidation (WO) catalysts using a bubbling reactor, where oxygen concentration is measured simultaneously in the liquid and in the gaseous phase. Total oxygen evolution is obtained from direct integration. The actual rate of oxygen formation as a function of time, R O 2 ( t ) not accessible to direct measurement with batch reactors, is calculated from raw data through a simple but comprehensive mathematical model, taking into account mass transfer phenomena occurring in the system. Data concerning the activity of a nanostructured Co3O4 catalyst dispersed on a mesoporous silica (MSU-H), in the presence of tris(2,2′-bipyridyl)Ruthenium [ Ru ( bpy ) 3 ] 2 + as sensitizer and Na2S2O8 as sacrificial reactant, are used to illustrate data processing. Behaviour of the system is complicated by the occurrence, besides WO reaction, of the degradation of the sensitizer. Increase of sweeping gas flow increases R O 2 ( t ) , by decreasing diffusional limitations to the reactions in the system: conditions for minimizing those were established. Data reported show that the assumption generally made of equilibrium between gaseous and liquid phase through Henry’s law is incorrect, the more so the smaller the apparent mass transfer coefficient, kLa. An additional reason for removing oxygen from the liquid phase through bubbling is the occurrence of a parasitic reaction of molecular oxygen with the sensitizer. The method seems to yield reliable values of both kLa and the set of R O 2 ( t ) values: the former scales with the flow of sweeping gas, as expected; R O 2 ( t ) curves are in qualitative agreement with accepted reaction mechanisms. Results concerning R O 2 ( t ) lend support to our previous kinetic studies (M. Armandi et al., ACS Catal, 2013, 3, 1272) where the reaction rate was assumed as constant for the first ∼15 min. Availability of R O 2 ( t ) data not too biased by diffusional limitations opens the way to realistic studies of the kinetic features of WO heterogeneous reactions, in the present case as well as in many others.

AbstractThe development of an “artificial leaf” that collects energy in the same way as a natural one is one of the great challenges for the use of renewable energy and a sustainable development. To avoid the problem of intermittency in solar energy, it is necessary to design systems that directly capture CO2 and convert it into liquid solar fuels that can be easily stored. However, to be advantageous over natural leaves, it is necessary that artificial leaves have a higher solar energy‐to‐chemical fuel conversion efficiency, directly provide fuels that can be used in power‐generating devices, and finally be robust and of easy construction, for example, smart, cheap and robust. This review discusses the recent progress in this field, with particular attention to the design and development of ‘artificial leaf’ devices and some of their critical components. This is a very active research area with different concepts and ideas under investigation, although often the validity of the considered solutions it is still not proven or the many constrains are not fully taken into account, particularly from the perspective of system engineering, which considerably limits some of the investigated solutions. It is also shown how system design should be included, at least at a conceptual level, in the definition of the artificial leaf elements to be investigated (catalysts, electrodes, membranes, sensitizers) and that the main relevant aspects of the cell engineering (mass/charge transport, fluid dynamics, sealing, etc.) should be also considered already at the initial stage because they determine the design and the choice between different options. For this reason, attention has been given to the system‐design ideas under development instead of the molecular aspects of the O2‐ or H2‐evolution catalysts. However, some of the recent advances in these catalysts, and their use in advanced electrodes, are also reported to provide a more complete picture of the field.

Abstract A new-designed transparent, conductive and porous electrode was developed for application in a compact laboratory-scale proton exchange membrane (PEM) photo-electrolyzer. The electrode is made of a thin transparent quartz sheet covered with fluorine-doped tin oxide (FTO), in which an array of holes is laser-drilled to allow water and gas permeation. The electrical, morphological, optical and electrochemical characterization of the drilled electrodes is presented in comparison with a non-drilled one. The drilled electrode exhibits, in the visible region, a good transmittance (average value of 62%), a noticeable reflectance due to the light scattering effect of the hole-drilled internal region, and a higher effective surface area than the non-drilled electrode. The proof-of-concept of the applicability of the drilled electrode was achieved by using it as a support for a traditional photocatalyst (i.e. commercial TiO 2 nanoparticles). The latter, coupled with a polymeric electrolyte membrane (i.e.Nafion 117) and a Pt counter electrode, forms a transparent membrane electrode assembly (MEA), with a good conductivity, wettability and porosity. Electrochemical impedance spectroscopy (EIS) was used as a very powerful tool to gain information on the real active surface of the new drilled electrode and the main electrochemical parameters driving the charge transfer reactions on it. This new electrode architecture is demonstrated to be an ideal support for testing new anodic and cathodic photoactive materials working in tandem configuration for solar fuels production by water photo-electrolysis.