Volume 96, Issue 4 - Special Issue: Avogadro Colloquia 2022

The fifth edition of Avogadro Colloquia entitled “From Water to Chemicals: Vision and Opportunities of a Sustainable Hydrogen Society”, jointly organized by the Department of Chemical Sciences and Materials Technologies of the National Research Council (DSCTM CNR) and the Italian Chemical Society (SCI), was held at the CNR headquarters in Rome on December 15 th –16 th , 2022. This relevant periodic conference of SCI also was one of the first events for the celebrations of the Centenary of the Italian CNR. This edition of the Colloquia was focused on the technologies for hydrogen production and use in the so-called green transition towards a society with reduced CO 2 emissions. Such technologies well fit the objectives recommended by the United Nations and by Mission EU2030 for the mitigation of the climate change. Greeting addresses to this event were given by the CNR president Maria Chiara Carrozza, the president of SCI Gaetano Guerra, the elected president of the European Chemical Society (EuChemS) Angela Agostiano, the IUPAC president Javier García Martínez and the director of DSCTM CNR Lidia Armelao. All the representatives of the national and international chemical societies underlined the key role of chemical sciences and innovative materials in the green transition.

Hydrogen can be used to sustain a revolutionary energy system, capable of integrating renewable sources and free from greenhouse gas emissions, in the perspective to mitigate global warming. Fuel cells and electrolyzers are the cornerstone of this new clean energy system, that is currently under research, development and implementation.

The development of new technologies for the current energy and environmental challenges requires the acquisition of a very fundamental knowledge about the structure and activity of catalytic materials at the nanometric scale. As a consequence, in situ and operando methodologies are blossoming, but only a fraction of them really aims at a local vision that would allow watching atoms at work during reactions. In this short report, we want to outline the merits of a new technique based on scanning tunnelling microscopy (Current-roughness electrochemical scanning tunneling microscopy, cr-EC-STM) which can visualize electrocatalytic reactions down at the single atom level. Results of two case studies in the field of hydrogen evolution reaction (HER) are briefly summarized, witnessing the capability of cr-EC-STM to provide critical information about the structure and catalytic performance of the active sites with atomic resolution.

Hydrogen is currently used as an intermediate product in the chemical (mostly ammonia and methanol) and refining industries. It is produced mostly from natural gas in large scale plants using steam methane reforming, a very mature technology. Hydrogen produced from natural gas has a high carbon footprint, considering that about 6–9 tons of CO 2 are co-produced (and emitted to the atmosphere) per ton of produced hydrogen, depending on natural gas composition. For this reason, hydrogen produced from fossil fuels is nowadays named as “grey” hydrogen. The current production of hydrogen is responsible of about 2.5 % of CO 2 emissions worldwide. For hydrogen remaining in business, and then becoming a factor in the energy transition period and later, decarbonizing its production is a must. Partially decarbonized hydrogen produced from fossil fuels, through CO 2 capture, is named “blue” hydrogen. A completely different path is followed for the production of fully decarbonized, or “green” hydrogen. This path is already commercially available, though on a smaller scale than required for wide industrial application. It is the electrolysis of water, i.e. the use of electric power from renewable sources to break the water molecule into its constituent hydrogen and oxygen. Pros & cons of these two options will be critically examined.

This contribution critically addresses the “green” H 2 production issue. After introducing the topic and the limits of the production of H 2 from electrolysis, some examples of alternative methods are discussed, highlighting the possibility of reducing costs, carbon footprint and intensity of use of renewable energy compared to electrolysis.

The use of molecular hydrogen (H 2 ) in the energy sector faces several technical and economic hurdles related to its chemical and physical properties, particularly volumetric energy density and mass. The production, transport and storage of hydrogen, both in gas and liquid form, are intrinsically inefficient and expensive. Moreover, the mass production of green hydrogen would preferably use surpluses of renewable electricity that will be largely available not before the next decade. To fulfill the great potential of H 2 in the decarbonization of the global economy – which should greatly accelerate – applications must be carefully selected, favoring for instance hard-to-abate sectors with respect to low-temperature residential heating or long-distance transportation versus light duty vehicles. In the meantime, research on production, transportation and storage of H 2 must substantially leap forward.

De Nora, an Italian multinational corporation listed on Euronext Milan, stands as a notable leader in sustainable technologies, especially within the growing field of green hydrogen. Over its century-long existence, the company has undergone distinct phases, culminating in a significant global role for a greener and more sustainable future. De Nora has substantiated its international presence with a robust network of 25 operational entities, five research centers, and a workforce exceeding 2000 employees. Originating in 1923 under Oronzio De Nora’s vision, the establishment of Oronzio De Nora Impianti Elettrochimici propelled the company into pioneering electrochemical advancements. Initially focusing on chlor-alkali technologies, De Nora’s strategic collaborations and acquisitions facilitated its evolution from a specialized enterprise to a versatile multinational entity. The contemporary phase of De Nora’s journey has been fortified by strategic partnerships, notably with Blackstone Tactical Opportunities and later Snam S.p.A. These alliances align with the need to face climate change and underscore De Nora’s commitment to achieving carbon neutrality by 2050. As the transition to cleaner energy solutions accelerates worldwide, De Nora’s expertise in electrode technology and electrochemical processes positions it as a frontrunner in the green hydrogen revolution. Central to this evolution is the rise of green hydrogen, produced through water electrolysis using renewable sources. De Nora’s research and development initiatives have yielded transformative outcomes, including energy-efficient electrodes and innovative electrode packages tailored for alkaline electrolysis. This focus on efficiency and cost reduction enhances De Nora’s potential to drive the widespread adoption of green hydrogen technology, amplifying its influence on the global energy landscape. De Nora’s impact extends to pivotal global initiatives, exemplified by its role as a strategic partner in NEOM project, an ambitious green hydrogen production facility in Saudi Arabia. Furthermore, De Nora’s contributions resonate in Europe’s largest green hydrogen generation project through collaboration with H2 Green Steel in Sweden. Moreover, a crowning achievement in De Nora’s trajectory is the visionary ‘GigaFactory’, a model of innovation and sustainability made in partnership with Snam. Located near Milan, this pioneering manufacturing hub will embody principles of Industry 4.0, flexibility and automation practices. Supported by the European IPCEI Hydrogen program and the European Commission, this initiative represents a significant stride towards a renewable hydrogen value chain. In conclusion, De Nora’s journey encapsulates a century-long evolution from its electrochemical roots to a dynamic global company propelling sustainable technologies. Anchored by an unwavering commitment to carbon neutrality and bolstered by transformative partnerships, the company embodies innovation and collaborative engagement – essential elements for steering industries towards a sustainable future. In a world united by the necessity of decarbonization, De Nora stands steadfast, carving its role as a symbol of a sustainable future.

In this article, we present an in-situ and operando time-resolved X-ray Absorption Spectroscopy (XAS) technique which exploits a combination of Grazing Incidence XAS (GIXAS) and Fixed Energy X-ray Absorption Voltammetry (FEXRAV), the Grazing Incidence FEXRAV (GI-FEXRAV). A case-study is also outlined. Palladium ultra-low loadings were deposited above Au polycrystalline iso-oriented substrates adopting three different deposition methods: surface-controlled electrochemical methods, direct electrodeposition, and physical vapour deposition (PVD). These catalytical surfaces were prepared for the investigation by GI-FEXRAV of the Pd oxidation/dissolution phenomenon that could occur when the metal is used in the anodic compartment of Direct Alcohol Fuel Cells (DAFCs) or in electrochemical reformers. Moreover, we report a robust, low cost and versatile procedure to obtain wide and flat iso-oriented gold substrates that can mimic monocrystalline gold (1 1 1) in the electrochemical response. The use of GI-FEXRAV for the operando characterization of the catalysts, in conjunction with the designed experimental cell and our flexible Au-based electrochemical substrates show an invaluable potential in the operando study of fundamental phenomena in heterogeneous electrocatalysis model systems and, due to its versatility, paves the way to further studies on a wide selection of electrochemical systems.

After production and before the use in different applications, hydrogen may need to be purified, transported, compressed and stored. Hydrogen is conventionally stored in high pressure gas cylinders and, as a liquid phase at low temperatures, in opened tanks. These methods present several economic and security problems. So, hydrogen storage in liquid or solid carriers is a suitable method for future applications. Hydrogen absorption and desorption in metal and complex hydrides will be discussed. Examples are provided, including the role of additives in promoting hydrogen sorption reactions. Some case studies using metal hydrides as hydrogen carrier are presented. The HyCARE project, focussed on the development of an efficient metal hydride-based system for the storage of renewables energies is presented, giving evidence of about 50 kg of hydrogen stored in metal hydrides. A small-scale hydrogen refuelling station developed to provide hydrogen for a fuel cell driven drone will be described. The Life Cycle Assessment (LCA) methodology to evaluate the environmental impacts associated with developed systems is also shortly described. Finally, main open challenges will be outlined, suggesting possible approaches for their overcoming.

Water electrolysis fed by renewable energy is the foremost technology to generate green hydrogen. Relevant challenges regard decrease of precious metal loadings and performance enhancement while maintaining cutting edge efficiency. Next generation electrolysers must provide dynamic behaviour to improve grid-balancing services and thus integrate with the grid the intermittent renewable energy sources. The HPEM2GAS project developed a low-cost optimised PEM electrolyser for grid management through both stack and balance of plant innovations.

Flexible electronics is a new generation of electronic devices in which electronic components are integrated into flexible substrates. It is used in the fabrication of displays, solar cells, integrated circuits, and increasingly in the fabrication of electronic skin (E-skin), which can mimic the properties of human skin by being able to follow skin movements and flexures without loss of mechanical and electrical properties. E-skin is suitable for integrating various sensors to monitor personal health. Conductive polymers are used in flexible electronics due to their electrical conductivity, low mass, and stability. However, their main disadvantage is their brittleness, which is why they don’t possess flexibility property without modification. Therefore, in this work, the conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was used as the main chain and the side branches of poly(acrylate-urethane) (PAU) were grafted onto it by atom transfer radical polymerization (ATRP) onto it, obtaining the grafted copolymer PEDOT- g -PAU. In this way, the main chain of PEDOT retains the property of electrical conductivity without losing conjugation, while the side branches of PAU have the ability to crosslink non-covalently through hydrogen bonds with PAU side branches of adjacent polymer molecules due to the presence of oxygen in their structure. The presence of hydrogen bonds allows increasing the stretchability and flexibility of the material, and they also have the ability to spontaneously renew themselves when they break due to excessive stress. Three different synthesis conditions were used to obtain polymers of different structure, which were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and measurement of electrical conductivity with a four-point probe (4PP) method. The obtained graft copolymer was prepared in the form of ink and printed on a polyurethane (PU) substrate using inkjet technique. The conductivity of the printed layer, its elongation and adhesion were investigated, while possible delamination of the printed polymer layer was also monitored. The results showed that the PEDOT- g -PAU copolymer was successfully synthesized and inkjet printing on PU film was successful. The obtained material has satisfactory electrical and mechanical properties and could be used for the integration of fully functional biosensors with further optimization of the composition.

Copper and copper-based compounds have broad spectrum antimicrobial activity, but concerns about leaching into the environment and toxicity on non-target organisms is leading the use of copper-based coatings being restricted. Our objective was to develop coatings that used the biocidal activity of copper, but with low negative impacts by reducing its leaching into the environment. This study reports the synthesis and characterisation of copper coordinating ligands, their formulation into coatings and testing of their antibacterial activity. A polyacylhydrazone and a series of simple acylhydrazones were synthesised and coordinated to Cu(II), but were considered unsuitable due to either their poor water-solubility or high levels of copper leaching. In an alternative approach, copper was successfully chelated to the tetraazamacrocycle, cyclen, and used to synthesise Cu(II)-cyclen functionalised silica particles, which were successfully combined with commercial paint formulations. These functionalised products showed poor antibacterial activity when incorporated into epoxy coatings, probably due to the low copper content of the formulations. However, these ligands may have other applications, such as removal of heavy metals from contaminated effluent steams.

Five randomly cross-linked amphiphilic copolymer networks (ACPN) were prepared via the free radical cross-linking copolymerization of the hydrophobic n -butyl acrylate (BuA) and the hydrophilic N , N -dimethylacrylamide (DMAAm), in the presence of a small amount (5 mol% with respect to the sum of BuA plus DMAAm monomers) of the hydrophobic 1,6-hexanediol diacrylate (HexDA) cross-linker, initiated by 4,4ʹ-azobis(4-cyanovaleric acid) in 1,4-dioxane at a 10 % w/v total monomer concentration. The five ACPNs differed in their BuA content, fixed at 10, 30, 50, 70 and 90 mol%. The two homopolymer networks, BuA and DMAAm, were also prepared using the same polymerization method. Thus, this study involved a total of seven polymer networks, forming a homologous series with BuA contents ranging from 0 to 100 mol%. These networks were characterized in terms of their degrees of swelling in tetrahydrofuran (THF) and water, their mechanical properties in water, and their adhesion to human skin. The degrees of swelling (DS) of the networks in THF were higher than those in water because THF is a non-selective solvent, whereas water is selective for the hydrophilic DMAAm units. The DSs in THF increased with the network content in the less polar BuA units, while the opposite was true for the DSs in water which decreased with the content in the hydrophobic BuA units from 11 (0 mol% BuA) down to 1.1 (100 mol% BuA). A maximum in the elastic modulus was observed for the hydrogel with 50 mol% BuA, reflecting the opposing effects of polymer composition in soft polymer (polyBuA) content and hydrogel water content. In contrast, the tensile strain at break increased monotonically with the hydrogel BuA content, reaching a remarkable ∼900 % for the hydrogel with 90 mol% BuA. Finally, the adhesion of the ACPNs, both in their dried and hydrated states, onto human skin was explored. The adhesion of the hydrated samples onto skin was stronger than that of the dried ones. The hydrated ACPN with 30 mol% BuA exhibited the strongest adhesion onto skin, attributable to the best combination of a rather high content in polar DMAAm units (70 mol%), and a rather low aqueous DS (∼2.5), with the low DS value causing only a small dilution in the DMAAm units participating in the polar interactions with skin. The present work demonstrates that, even in this synthetically simple ACPN system, the multiple effects of ACPN composition on a certain property, in some cases opposing and in some other cooperating, lead to a rather complicated behavior. In particular, as the BuA content increases, some properties display maxima (elastic modulus, stress at break and fracture energy of hydrated ACPNs, and adhesion of hydrated ACPNs onto skin) while some other properties exhibit monotonic increases (strain at break of hydrated ACPNs, and adhesion of dried ACPNs onto skin). Thus, the optimal ACPN for a particular application will highly depend on the property best-serving the particular application, e.g. , the ACPNs with 30, 50 and 90 mol% BuA for strongest wet adhesion to skin, stiffest hydrogel response, and highest hydrogel extensibility and toughness, respectively.

It is widely recognized that electrostatics plays a central role in the intermolecular interactions in condensed phases, as evidenced by the “electrostatics + Lennard-Jones” form of the potential functions that are commonly used in classical molecular dynamics simulations. Then, do we understand all about electrostatics in condensed phases? In this review, recent theoretical advances in relation to this topic will be discussed: (1) vibrational spectroscopic probing of the electrostatics in condensed phases, and (2) some phenomena affected by deviation from the scheme of isotropic fixed atomic partial charges, i.e. , anisotropy and intermolecular transfer of electron distributions. A theoretical basis for better understanding on them and some theoretical models for practical calculations will be shown with some typical example cases of hydrogen- and halogen-bonded systems.

Chemical speciation studies, i.e., the study of the distribution of an element or compound among its various species in a system of interest, are of fundamental importance. Chemical speciation investigations can be performed mainly by either the direct measurement of the chemical species by different analytical techniques, or by chemical modeling through equilibrium thermodynamic data, based on the use of stability constants (and other thermodynamic parameters) of the formed species. For these purposes, a series of techniques can be used. As soon as the complexity of the systems of interest increases, the need for more detailed information arises. As such, a multi-technique approach is essential to derive complementary data to define a chemical system. In this tutorial review we analyzed the most common instrumental techniques employed for chemical speciation studies and equilibrium data analysis. The main advantages and disadvantages of potentiometry, voltammetry, coulometry, UV–vis spectrophotometry, spectrofluorimetry, NMR, EPR, ITC, HRMS and quantum mechanical calculations, together with brief mention to other less common techniques, are discussed together with a series of practical examples of their application. The main aim of this tutorial review is to provide a practical guide to all scientists interested in the field.