Membrane technology is recognized to be unique in many industrial sectors. This technology contributes significantly to sustainable development promoted by the principles of Green Chemistry and Process Intensification Strategy (PI). It has become a successful alternative technology that led to significant benefits concerning the conventional separation techniques, such as ease of processability, flexibility, and small footprints making them the preferred choice in many fields of interest. In this overview, the vision for the future development of membrane operations is evidenced and it is based on the improvement of existing membrane processes for specific applications, such as hydrogen production, food sector, and distillation, by using membrane reactors, bioreactors, and membrane distillation (MD) processes, respectively. Furthermore, to enhance the sustainability throughout the lifecycle of membrane products, the exploitation of new solvents and biopolymers platforms that have great potential to replace hazardous solvents or petroleum-based materials for more sustainable membranes in different geometries is presented and discussed.

Visible-light-driven splitting of water into oxygen and hydrogen is an attractive way to convert solar energy into fuels: artificial photosynthesis and dye-sensitized photoelectrochemical cells (DS-PECs), have been deeply investigated as a promising route to convert solar energy into renewable hydrogen fuel. A crucial strategy to increase the efficiency of DS-PEC is the optimization of the dye used in the sensitization of nanostructured TiO2 photoanode that must match with the ruthenium complex used as water oxidation catalyst (WOC). Our goal is the design, synthesis, and optimization of a metal-free sensitizer having D(donor)-?-A(acceptor) structure and photoelectrochemical properties for applicability in DS-PEC. In this study, we report the synthesis of the dye 1 (Figure 1), based on a dioctyl-4H-silolo[3,2-b:4,5-b'] dithiophene central cores and having a 2-cyanoacrylic acid as acceptor group and a 4-(4-methoxyphenyl) benzo[c] [1,2,5] thiadiazol as donor group. The challenging synthesis was optimized through recent approaches as direct arylation reactions instead of common C-C bond formation by Pd-catalyzed cross coupling reactions.

In the field of artificial photosynthesis, dye-sensitized photoelectrochemical cells (DS-PECs) for water-splitting have been extremely investigated in the last years in the effort to provide a reliable system to produce solar fuels from water and sunlight. Given the crucial role of the dye in the working mechanism of the device, the design and synthesis of novel sensitizers with a broad optical response, appropriate energy levels, and good stability represents a key-point. Among the different classes of sensitizers employed for such a process, organic metal-free dyes, and especially D (donor)-pi-A (acceptor) sensitizers, have been intensely investigated thanks to their low cost, tunable spectroscopic properties, good stability and relatively easy synthesis. In this study, we report the design and synthesis of a family of five new metal-free organic dyes, based on quinoxaline (compound 1a-c) and pyrido-pirazine (compounds 2,3) central cores. Moreover, we explored their potential application as sensitizers in DS-PECs in combination with the chosen water oxidation catalyst: Ru(bda)(pyP)2 (pyP = pyridin-4-methyl phosphonic acid). All the compounds have been successfully synthesized, with good overall yields, through well-known Pd-catalysed C-C cross coupling reactions, such as Suzuki-Miyaura and Stille reactions, or, when possible, through more recent approaches like direct C-H activation reactions. Preliminary studies, such as absorption and emission spectra and cyclic voltammetry, have been also carried out in order to evaluate their photoelectrochemical properties and applicability in the device.

In a growing global energy demand combined with the excessive use of fossil fuels, renewable sources of energy are considered a good alternative to avoid the use of hydrocarbon deposit. In this scenario visible light-driven splitting of water into oxygen and hydrogen is an attractive way to convert solar energy into fuels: artificial photosynthesis and dye-sensitized photoelectrochemical cells (DS-PECs), have been deeply investigated as a promising route to convert solar energy into renewable hydrogen fuel. A crucial strategy to increase the efficiency of DS-PEC is the optimization of the dye used in the sensitization of nanostructured TiO2 photoanode that must match with the ruthenium complex used as water oxidation catalyst (WOC). Our goal is the design, synthesis, and optimization of a metal-free sensitizer having D(donor)-?-A(acceptor) structure and photoelectrochemical properties for applicability in DS-PEC. In this study, we report the synthesis of the dye 1 (figure), based on a dioctyl-4H-silolo[3,2-b:4,5-b']dithiophene central cores and having a 2-cyanoacrylic acid as acceptor group and a 4-(4-methoxyphenyl)benzo[c] [1,2,5] thiadiazole as donor group. The challenging synthesis was optimized through recent approaches as direct arylation reactions instead of common C-C bond formation by Pd-catalyzed cross coupling reactions.

In the field of artificial photosynthesis, dye-sensitized photoelectrochemical cells (DS-PECs) for water-splitting have been extremely investigated in the last years in the effort to provide a reliable system to produce solar fuels from water and sunlight. Given the crucial role of the dye in the working mechanism of the device, the design and synthesis of novel sensitizers with a broad optical response, appropriate energy levels, and good stability represents a key-point. Among the different classes of sensitizers employed for such a process, organic metal-free dyes, and especially D (donor)-p-A (acceptor) sensitizers, have been intensely investigated thanks to their low cost, tunable spectroscopic properties, good stability and relatively easy synthesis. In this study, we report the design and synthesis of a family of five new metal-free organic dyes, based on quinoxaline (compound 1a-c) and pyrido-pirazine (compounds 2,3) central cores. Moreover, we explored their potential application as sensitizers in DS-PECs in combination with Ru-based water oxidation catalysts. All the compounds have been successfully synthetized, with good overall yields, through well-known Pd-catalysed C-C cross coupling reactions, such as Suzuki-Miyaura and Stille reactions, or, when possible, through more recent approaches like direct C-H activation reactions. Preliminary studies have been also carried out in order to evaluate their photoelectrochemical properties and applicability in the device.

Dye-sensitized photoelectrochemical cells (DS-PECs) for water-splitting are receiving increasing attention as a novel technology for visible light-induced solar fuels production. The water oxidation reaction, occurring at the photoanode (PA), represents the key rate-determining step in water splitting, therefore the assembly of efficient and stable photoanodes is an essential part of DS-PECs. Beside the semiconductor (SC) oxide and the water oxidation catalyst (WOC), the role of the dye is crucial for optimizing the harvesting of visible light and triggering the oxidation reaction at the catalytic active site. Most of the dyes tested to date in PA-DS-PEC for water splitting show a narrow absorption spectrum (?max<450 nm) and poor stability. Therefore, the design of dye molecules with a broad optical response, appropriate energy levels, and good stability is urgently needed. In this study, three novel metal-free organic dyes (1a-c), based on a quinoxaline central core, have been investigated as possible anode sensitizers. Compounds 1a-c contains three slightly different donor moieties in order to modulate their HOMO energy level and use them in combination with the chosen WOC: Ru(bda)(pyP)2 (pyP =pyridin-4-methyl phosphonic acid). All the compounds have been successfully obtained through a simple and general synthetic method leading to good overall yields. Preliminary studies, such as absorption and emission spectra and cyclic voltammetry, have been also carried out in order to evaluate their photoelectrochemical properties. All three compounds show promising energy levels, especially dye 1c, for possible application in PA-DS-PEC.

Defect-engineering is a viable strategy to improve the activity of nanocatalysts for the oxygen evolution reaction (OER), whose slow kinetics still strongly limits the broad market penetration of electrochemical water splitting as a sustainable technology for large-scale hydrogen production. High-entropy spinel oxides (HESOs) are in focus due to their great potential as low-cost OER electrocatalysts. In this work, electrospun HESO nanofibers (NFs), based on (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, with granular architecture and oxygen-deficient surface are produced by calcination at low temperature (600 or 500 °C), characterized by a combination of benchtop analytical techniques and evaluated as electrocatalysts for OER in alkaline medium. The variation of HESO composition and calcination temperature produces complex and interdependent changes in the morphology of the fibers, crystallinity and inversion degree of the spinel oxide, concentration of the oxygen-vacancies, cation distribution in the lattice, which mirror on different electrochemical properties of the fibers. The best electrocatalytic performance (overpotential and Tafel slope at 10 mA cm: 360 mV and 41 mV dec, respectively) pertains to (CrMnFeCoNi)O NFs calcined at 500 °C and results from the lower outer 3d-electron number, e filling closer to its optimal value and higher occupation of 16d sites by the most redox-active species.

The existing literature survey reports rare and conflicting studies on the effect of the preparation method of metal-based semiconductor photocatalysts on structural/morphological features, electronic properties, and kinetics regulating the photocatalytic H-2 generation reaction. In this investigation, we compare the different copper/titania-based photocatalysts for H-2 generation synthesized via distinct methods (i.e., photodeposition and impregnation). Our study aims to establish a stringent correlation between physicochemical/electronic properties and photocatalytic performances for H-2 generation based on material characterization and kinetic modeling of the experimental outcomes. Estimating unknown kinetic parameters, such as charge recombination rate and quantum yield, suggests a mechanism regulating charge carrier lifetime depending on copper distribution on the TiO2 surface. We demonstrate that H-2 generation photoefficiency recorded over impregnated CuxOy/TiO2 is related to an even distribution of Cu(0)/Cu(I) on TiO2, and the formation of an Ohmic junction concertedly extended charge carrier lifetime and separation. The outcomes of the kinetic analysis and the related modeling investigation underpin photocatalyst physicochemical and electronic properties. Overall, the present study lays the groundwork for the future design of metal-based semiconductor photocatalysts with high photoefficiencies for H-2 evolution.

The only strategy for reducing fossil fuel-based energy sources is to increase the use of sustainable ones. Among renewable energy sources, solar energy can significantly contribute to a sustainable energy future, but its discontinuous nature requires a large storage capacity. Due to its ability to be produced from primary energy sources and transformed, without greenhouse gas emissions, into mechanical, thermal, and electrical energy, emitting only water as a by-product, hydrogen is an effective carrier and means of energy storage. Technologies for hydrogen production from methane, methanol, hydrocarbons, and water electrolysis using non-renewable electrical power generate CO2. Conversely, employing photoelectrochemistry to harvest hydrogen is a sustainable technique for sunlight-direct energy storage. Research on photoelectrolysis is addressed to materials, prototypes, and simulation studies. From the latter point of view, models have mainly been implemented for aqueous-electrolyte cells, with only one semiconductor-based electrode and a metal-based counter electrode. In this study, a novel cell architecture was numerically modelled. A numerical model of a tandem cell with anode and cathode based on metal oxide semiconductors and a polymeric membrane as an electrolyte was implemented and investigated. Numerical results of 11% solar to hydrogen conversion demonstrate the feasibility of the proposed novel concept.

The development of innovative technologies based on employing green energy carriers, such as hydrogen, is becoming high in demand, especially in the automotive sector, as a result of the challenges associated with sustainable mobility. In the present review, a detailed overview of the entire hydrogen supply chain is proposed, spanning from its production to storage and final use in cars. Notably, the main focus is on Polymer Electrolyte Membrane Fuel Cells (PEMFC) as the fuel-cell type most typically used in fuel cell electric vehicles. The analysis also includes a cost assessment of the various systems involved; specifically, the materials commonly employed to manufacture fuel cells, stacks, and hydrogen storage systems are considered, emphasizing the strengths and weaknesses of the selected strategies, together with assessing the solutions to current problems. Moreover, as a sought-after parallelism, a comparison is also proposed and discussed between traditional diesel or gasoline cars, battery-powered electric cars, and fuel cell electric cars, thus highlighting the advantages and main drawbacks of the propulsion systems currently available on the market.

A nickel ferrite was prepared by a liquid-phase method and used as an oxygen evolution catalyst in an anion exchange membrane electrolyser. A complete physicochemical characterization of the catalyst was performed through X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Then, the nickel ferrite was deposited by spray coating technique onto a Fumasep (R) FAA3-50 anion-exchange membrane to realize a catalyst-coated membrane (CCM), and tested in a 5 cm(2) single cell setup in the so-called zero-gap configuration. At 60 degrees C and 2.2 V, a current density of 3 A/cm(2) was reached, which is higher than that obtained with NiO and IrO2 commercial catalysts. Moreover, a chronoamperometric test of 120 h highlighted the good stability of the synthesized catalyst.

The increase in the global energy demand, which is mainly provided by the utilization of fossil fuels, has caused both a significant increase in environmental problems and a depletion in the fossil fuel reserves. This situation has also led to concerns related to future energy supply; and therefore, the interest in alternative fuel production by the use of new technologies has increased. In this regard, membrane reactors, which can provide the desired fuel production and separation in the same reactor, have taken significant attention recently. In this chapter, hydrogen and synthetic fuel production from different renewable sources through the use of a membrane reactor are presented in detail. Firstly, a categorization of membrane reactors is done according to membrane types (nature, housing, and separation regime) and membrane reactor configurations (packed-bed, fluidized-bed, and hollow-fiber micro membrane reactors). A comparison between the membrane reactor and the conventional reactor is also made in terms of their advantages and disadvantages. Secondly, some discussions on hydrogen production using membrane reactors through the utilization of fuel obtained from renewable sources such as biomass-derived biofuel and ammonia are given, and various studies on this topic found in the literature are investigated and discussed. Finally, a discussion on synthetic fuel production using membrane reactors through the utilization of renewable resources is given.

Hydrogen has the largest energy density of all fuels and is considered the more suitable energy source (properly H2 is an energy vector) for matching a clean and carbon neutral future energetic scenario. This rather old technology was theorized almost 50 years ago but still doesn't have a widespread application due to severe limitations. The high cost and the poor sustainability for large scale application of electrochemical devices for hydrogen production and conversion to electricity are the main limitations. In fact, proton exchange membrane electrolyzers (PEMs) and fuel cells (PEMFCs) employ catalysts based on high amounts of rare noble metals, such as Pt, Ir, Ru and Pd. In addition, proton exchange membranes, such as the DuPont Nafion®, are very expensive materials. The reduction of precious metal loadings to negligible amounts keeping constant catalyst activity is a possible route for making fuel cells and electrolyzers sustainable devices. Traditional electrocatalysts are based on metal nanoparticles dispersed on conductive supports where only the particles surface atoms are involved in electrocatalysis. Replacing nanoparticles with metal complexes is a way for making accessible each metal center of the catalyst. A molecular catalyst offers other advantages with respect to nanosized materials, such as control of the selectivity of the oxidation reaction occurring in direct fuel cells fed with liquid and renewable fuels such as alcohols and formic acid. So direct fuel cells can convert a biomass-derived fuel not only into electricity but also into high purity chemicals. A second route to make fuel cells and electrolyzers sustainable devices is the replacement of proton exchange membranes with anion exchange membranes (AEMs) because in alkaline environment several nanostructured catalysts based on cheap metals can be used (in acidic environment most of the transition metals would be subject to corrosion phenomena). Thanks to the development over the last few years of high efficiency and stable alkaline membranes, we have developed anodic and cathodic nanostructured catalysts based on cheap metals like iron and nickel which are assembled together in alkaline fuel cells and eletrolyzers able to reach an activity close to the state of the art PEM based devices. As example an iron phthalocyanine cathode based H2/O2 fed fuel cell set up in our laboratory delivered a remarkable power density of 1 W cm-2.

The most widely used process for hydrogen production is steam methane reforming. It can be carried out using a membrane reactor in which simultaneous hydrogen production and purification occur. Mathematical modeling of these reactors plays a key role in the selection of the design and operating parameters that yield high performance for the reactor. This review study discusses, synthesizes, and compares different mathematical modeling studies on the packed bed membrane reactors for hydrogen production from methane found in the literature. Different approaches used in these modeling studies for the hydrogen permeation steps, reaction kinetic expressions, phases involved (pseudo-homogeneous and heterogeneous), and spatial dimensions (one, two, and three dimensional) are given.

L'attività del secondo semestre all'interno del progetto SOS ACQUA (Sistema per la decontaminazione e di produzione di energia dall'acqua) è stata focalizzata all'ottimizzazione delle performance di foto-elettrodi a base di rame prodotti mediante gli inchiostri (denominati Ink_25 e 55_Cu) che hanno dimostrato le migliori proprietà in termini di produzione di idrogeno (RT 88/2020) nel semestre precedente. Di questi sistemi è stata inizialmente studiata la dipendenza tra spessore e proprietà per poi considerare l'utilizzo di un materiale conduttivo (platino) e/o l'assorbimento di un co-catalizzatore a base metallica al fine di ottimizzarne le performance e la durabilità.

L'attività del primo semestre all'interno del progetto SOS ACQUA (Sistema per la decontaminazione e di produzione di energia dall'acqua) è stata principalmente focalizzata su i) analisi dello stato dell'arte, ii) identificazione dei materiali più idonei per la produzione del foto-catodo e, iii) caratterizzazione chimico-fisica, morfologica e prestazionale dei materiali selezionati. I risultati derivanti dal primo punto sono stati descritti nella 1° relazione (Analisi dello stato dell'arte, selezione dei materiali e piano sperimentale, protocollo ISTEC 1864 del 29-09-2020) mentre, gli esisti relativi all'identificazione dei materiali più idonei e loro caratterizzazione sono invece ampliamente trattati in questo documento. In questo rapporto sono in particolar modo riportati i risultati relativi allo studio di materiali volti ad individuare i sistemi più adatti per la produzione di idrogeno mediante reazione di water splitting in cella foto-elettrochimica. Le classi di materiali prese in considerazione sono state: Cu2O/CuO, LaFeO3 (LF), La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), La0.8Sr0.2MnO3 (LSM), La0.1Sr0.9TiO3 (LST). Per ciascuna di esse sono state ampiamente caratterizzate le polveri di partenza da un punto di vista morfologico-strutturale e di superficie specifica; è stata inoltre valutata l'attività foto-catalitica tramite reazione con una molecola modello (Rodamina B). Dopo un attento studio di formulazione sono stati prodotti e selezionati inchiostri idonei per la deposizione di film elettrodici sottili su un supporto vetroso mediante serigrafia. Degli elettrodi così ottenuti sono state accuratamente valutate le proprietà elettrochimiche e fotoelettrochimiche. Sui composti con le caratteristiche più promettenti sono state eseguite misure di produzione di idrogeno trmite cella fotoelettrochimica.

Nanostructured gels have emerged as an attractive functional material to innovate the field of energy, with applications ranging from extraction and purification to nanocatalysts with unprecedented performance. In this review we discuss the various classes of nanostructured gels and the most recent advancements in the field with a perspective on future directions of this challenging area.

Oxygen evolution reaction (OER) is a demanding step within the water splitting process for its requirement of a high overpotential. Thus, to overcome this unfavourable kinetics, an efficient catalyst is required to expedite the process. In this context, we report on Ni foam functionalised with low cost iron (Fe) and iron hydroxide (Fe(OH)(X)), wet chemically synthesized as OER catalysts. The prepared catalyst based on iron hydroxide precipitate shows a promising performance, exhibiting an overpotential of 270 mV (at a current density of 10 mA cm(-2)in 1 M KOH solution), an efficient Tafel slope of similar to 50 mV dec(-1)and stable chronopotentiometry. The promising performance of the anode was further reproduced in the overall water splitting reaction with a two electrode cell. The overall reaction requires a lower potential of 1.508 V to afford 10 mA cm(-2), corresponding to 81.5% electrical to fuel efficiency.

Photocatalysis and electrolysis are crucial processes for the development of a sustainable, clean energy system, since they enable solar fuel production, such as hydrogen by water splitting, as well as CO reduction. In these processes efficient and robust catalysts for water oxidation are required and the reduction of employed amount of noble metals is crucial to reduce costs and increase the sustainability of the technology. To obtain extremely low iridium loading on nickel foam electrodes we have employed electroless deposition by spontaneous galvanic displacement as a simple, low cost, highly scalable technique. After deposition the Ir oxidation has been achieved by annealing in air at 250 °C. By varying the deposition parameters, an optimal condition has been achieved, with an overpotential for water oxidation of 360 mV at 10 mA cm in 1.0 M KOH solution. The Ni foam coverage with Ir oxide has also a positive impact on the electrode stability, strongly decreasing the degradation rate, compared to the case of bare Ni foam. The average amount of noble metal in the best performing electrode is only 35 ?g cm for a 1.6 mm thick Ni foam electrode. The proposed approach is highly promising for gas diffusion electrodes, and can be implemented in electrolytic cells, as well as in fuel cells.