Electrochemical energy conversion and storage (EECS) devices are a family of systems that are playing a major role in today’s efforts worldwide to decarbonize the energy infrastructure, with the ultimate goal to mitigate the greenhouse effect and reduce global warming [1]. Though EECS devices include very diverse systems such as secondary batteries, fuel cells, redox flow batteries and supercapacitors, among many others, all EECS devices share the same basic components i.e. , two electrodes (where redox process take place) sandwiching a separator that allows for the selective transport of ions. In particular, the separator plays a crucial role to set some of the most relevant features of every EECS device, including the maximum power density that it can express and the durability/cyclability. Ionic liquids (ILs) have demonstrated a huge potential to enable the realization of EECS devices exhibiting an improved performance and durability. This feat is possible by leveraging on the unique features of ILs, with a particular reference to their highly customizable chemistry [2]. Suitable synthetic approaches allow to obtain systems specifically tailored to a certain application. In some instances, the best electrolytes are achieved by: (i) using the IL to soak a suitable matrix ( e.g. , a perfluorosulfonic acid derivative); (ii) dissolving a suitable dissociable compound ( e.g. , LiTFSI or δ-MgCl 2 ) into the IL; and/or (iii) dispersing a suitable inorganic filler into the IL. The resulting IL-based electrolytes exhibit the desired features in terms of: (i) chemistry of the mobile species ( e.g. , the proton, lithium complexes, magnesium species); (ii) facile and selective transport of such mobile species; (iii) good compatibility with the electrodes, allowing an efficient plating/stripping of the desired metal species and minimizing undesired parasitic reactions; (iv) broad electrochemical stability window (ESW); and (v) well-controlled hydrophilicity/hydrophobicity features. The present contribution overviews our activities in the synthesis, characterization and implementation into various EECS device prototypes of IL-based electrolytes. The latter include: (i) electrolytes for proton-exchange membrane fuel cells (PEMFCs) obtained by swelling a perfluorosulfonic acid derivative with proton-conducing ionic liquids (PCILs) [3]; (ii) hybrid electrolytes for lithium batteries obtained by dispersing suitable inorganic fillers into ILs [4]; (iii) catenated ILs for multivalent batteries obtained by dissolving magnesium/aluminum/titanium halides into suitable ILs [5]; and (iv) highly hydrophobic ILs for special applications [6]. Particular efforts are dedicated to elucidate the complex interplay between: (i) the synthetic parameters; (ii) the physicochemical properties; (iii) the electric response; (iv) the long-range charge transport mechanism; and (v) the performance and durability of the IL-based electrolyte upon implementation into an EECS device prototype. Acknowledgments This work received funding from the U.S. Army Research Office under the grant W911NF-21-1-0347, from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 829145 (FETOPEN-VIDICAT) and from the University of Padova under the grant BIRD2121_01. References [1] P. Poizot et al. , Energy Environ. Sci. 4, 2003-2019 (2011). [2] M. Armand et al. , Nature Materials 8, 621-629 (2009). [3] V. Di Noto et al. , J. Am. Chem. Soc., 132, 2183-2195 (2010). [4] F. Bertasi et al. , Electrochim. Acta 307, 51-63 (2019). [5] G. Pagot et al. , J. Power Sources, 524, 231084 (2022). [6] F. Bertasi et al. , Phys. Chem. Chem. Phys., 19, 26230–26239 (2017).

Several families of electrochemical energy conversion and storage devices (e.g., fuel cells and metal-air batteries) exploit the oxygen reduction reaction (ORR) in their operation. Very often, the ORR is the slowest electrochemical process in these systems and plays the most relevant role to degrade their energy conversion efficiency. Thus, to devise high-performing ORR electrocatalysts (ECs) is of crucial importance for practical applications. Unfortunately, to understand in detail the operating mechanism of an ORR EC is typically complex and time-consuming, requiring the implementation of a broad spectrum of advanced techniques and extensive data analysis. Consequently, there is a strong need to design simple methods capable to yield information on the most critical features of an ORR EC for screening purposes. In this regard, cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) is a very popular approach. The latter allows for the facile study of the kinetics of an electrochemical process as promoted by an EC and minimizes the influence of complex spurious phenomena (e.g., charge and mass transport). In this contribution a general method is discussed allowing for the correlation of the outcome of conventional electrochemical experiments with the critical features determining the performance of an ORR EC. Such features include prominently: (i) the kinetic activation barrier of the ORR; and (ii) the accessibility of O2 to the active sites. The proposed method: (i) adopts the CV-TF-RRDE setup; (ii) does not lean on the simplifications associated with the conventional Butler-Volmer kinetic description of electrochemical processes; and (iii) does not make assumptions on the specific features of the EC. As a result, the proposed method allows to compare accurately the kinetic performance of ORR ECs exhibiting a completely different chemistry. Finally, it is shown that the figure of merit considered in this method, E(j Pt(5%)), is much more accurate than other popular figures of merit to gauge the ORR such as the half-wave potential E1/2. Acknowledgements This research has received funding from (a) the European Union’s Horizon 2020 research and innovation program under grant agreement 881603 (b) the project ‘Advanced Low-Platinum hierarchical Electrocatalysts for low-T fuel cells’ funded by EIT Raw Materials, (c) Alkaline membranes and (platinum group metals)-free catalysts enabling innovative, open electrochemical devices for energy storage and conversion d AMPERE, FISR 2019 project funded by the Italian Ministry of University and Research, and (d) the project ‘Hierarchical electrocatalysts with a low platinum loading for low-temperature fuel cells d HELPER’ funded by the University of Padova. PJK and IAR (University of Warsaw) were supported in part by the National Science Center (NCN, Poland) under Opus Project 2018/29/B/ ST5/02627.

New inorganic-organic hybrid anion exchange membranes are produced after incorporation of tantalum oxide into trimethylammonium-functionalized polyethylene pyrrole-co-polyethylene ketone (functionalized polyketone, FPK), obtained by the chemical modification of a polyketone polymer. The influence of tantalum oxide fillers on the properties of the synthesized membranes is investigated. The interaction between inorganic fillers and the polymer chains is studied using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR). The thermal analysis of the FPK membranes reveals they are thermally stable at up to 250 degrees C. However, the incorporation of the inorganic fillers reduces the thermal stability. Modulated Differential Scanning Calorimetry (MDSC) results indicate that the inclusion of inorganic fillers leads to an increase in crystallinity. This study reports that the properties of the bulk polymer can be tuned by controlling the degree of functionalization and content of inorganic fillers, as confirmed by Near Ambient Pressure X-Ray Photoelectron Spectroscopy (NAP-XPS) studies. Finally, Broadband Electrical Spectroscopy (BES) studies demonstrate that the hybrid membranes are characterized by several polarization phenomena contributing to the overall ion conductivity of the material, which at RT is of 1.46 and 1.61 mS cm(-1) for the FPK cast membrane and the hybrid membrane with 5.0 wt.% of Ta2O5 filler, respectively.

Vanadium Redox Flow Batteries (VRFBs) are considered as a key technology in the field of large-scale energy storage systems [1, 2]. Unfortunately, their capabilities are compromised by the crossover of active species through the membrane which reduces the overall efficiency during operation and hinders the long-term capacity storage [3]. In this work, an extremely selective proton exchange material is proposed. “Zip-like” Ion Exchange Membranes (ZIEMs) are prepared by means of an acid-base reaction between the cationic and anionic functionalities of two interacting ionomers. The strong electrostatic crosslinking interactions between the two components generate an overall improvement of thermal and mechanical properties, and the permeation of vanadium ions is strongly hindered (the best performing membrane has a selectivity of 3.1⸱10 5 S⸱min⸱cm -3 , which is almost 50 times higher than Nafion). The best performing membranes show outstanding VRFB performance with a stable coulombic efficiency (>98% at 50 mA⸱cm -2 ), and a retained capacity of 82% after 100 cycles compared to the 21% of the same device with a Nafion 212 membrane. The results presented here show how ZIEM family of membranes can be regarded among the best performing ion exchange membranes up-to-date. Acknowledgements The authors wish to thank the fruitful collaboration within the project “Development of high-selectivity ion-exchange membranes for application in next-generation redox flow batteries” funded by ENI S.p.A., contract 2500026228. In addition, the authors wish to thank the SID2020Project of the Department of Industrial Engineering, University of Padova “A New frontier in Hybrid Inorganic-Organic Membranes for Energy Con-version and Storage Devices” (Prot. BIRD201244) for funding. References [1] R.K. Emmett, M.E. Roberts, Recent developments in alternative aqueous redox flow batteries for grid-scale energy storage, Journal of Power Sources, 506 (2021) 230087. [2] C. Sun, E. Negro, A. Nale, G. Pagot, K. Vezzù, T.A. Zawodzinski, L. Meda, C. Gambaro, V. Di Noto, An efficient barrier toward vanadium crossover in redox flow batteries: The bilayer [Nafion/(WO 3 ) x ] hybrid inorganic-organic membrane, Electrochimica Acta, 378 (2021) 138133. [3] V. Di Noto, K. Vezzù, G. Crivellaro, G. Pagot, C. Sun, L. Meda, I.A. Rutkowska, P.J. Kulesza, T.A. Zawodzinski, A general electrochemical formalism for vanadium redox flow batteries, Electrochimica Acta, 408 (2022).

This report describes a general method to correlate the features determining the performance of an electrocatalyst (EC), including the accessibility of O2 to the active sites and the kinetic activation barrier, with the outcome of conventional electrochemical experiments. The method has been implemented for oxygen reduction reaction ECs by cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) setup. The method: (i) does not rely on the simplifications associated with the Butler-Volmer kinetic description of electrochemical processes and (ii) does not make assumptions on the specific features of the EC, allowing to compare accurately the kinetic performance of oxygen reduction reaction ECs with completely different chemistry. Finally, with respect to other widespread figures of merit (e.g., the half-wave potential E1/2), the figure of merit here proposed, E(jPt(5%)), allows for much more accurate comparisons of the kinetic performance of ECs.

A major restructuring of the energy system is underway at the global level, with the purpose to curtail the dependence from fossil fuels and minimize the emissions of greenhouse gases [1]. Thus, a shift of paradigm is necessary towards the widespread implementation of innovative energy conversion and storage technologies. In this regard, a pivotal role is to be played by electrochemical energy conversion and storage (EECS) systems owing to their independence from geographical constrains, facile scalability and outstanding efficiency [2]. Among the different families of EECS, the technology of proton exchange membrane fuel cells (PEMFCs) is expected to play a pivotal role in such a milieu. Indeed, PEMFCs are compact and do not require moving parts. Hence, PEMFCs are ideal for application in light-duty vehicles or in small-size stationary applications such as auxiliary power units (APUs) and household systems able to store reversibly the energy obtained from renewables [3]. PEMFCs also exhibit an energy conversion efficiency that is two-three times larger with respect to that of competing traditional technologies such as internal combustion engines (ICEs) [4]. PEMFCs operate by converting into electrical energy the chemical energy associated with the oxidation of hydrogen. One of the most important bottlenecks in this process is the oxygen reduction reaction (ORR), that takes place at the PEMFC cathode. The ORR is sluggish and it must be promoted by suitable electrocatalysts (ECs) to ensure that the PEMFC achieves a performance level compatible with the intended application [5]. The most effective ORR ECs for PEMFCs include active sites based on platinum, whose scarcity in Earth’s crust triggers the risk to incur in supply bottlenecks [6]. This is a major drawback inhibiting the large-scale rollout of PEMFCs. Hence, the development of ECs that are high-performing, durable and comprise a low loading of platinum (giving so rise to “Low-Pt ECs”) is a major goal of PEMFC research. This work overviews the development of a new family of low-Pt ECs for the ORR. The active sites of the ECs are found on the surface of sub-nanometric clusters (SNCs) consisting of PtMx alloys, where M is a first-row transition metal (e.g., Ni, Cu). M operates as a “co-catalyst” and raises the intrinsic performance of each active site much above the Pt baseline [7]. With respect to the Pt nanoparticles (NPs) adopted in state-of-the-art ORR ECs, the SNCs increase the utilization of Pt atoms included therein by up to ca. one order of magnitude and make them much more available for electrocatalytic purposes. Consequently, the specific power yielded by the PEMFCs including the proposed low-Pt ECs is significantly raised. Values as high as 14 kW/gPt are achieved, that exceed the target set by the DoE for 2020 (i.e., 8 kW/gPt) [8]. The support of the low-Pt ECs described here exhibits a “core-shell” morphology; it comprises a hierarchical graphene-based (H-GR) “core” that is covered by a carbon nitride (CN) “shell”. H-GR consists of a combination of: (i) highly defected graphene nanoplatelets; and (ii) carbon black NPs [9]. The resulting system provides a broad surface area and allows for the facile transport of mass and charge through the system. The CN “shell” includes less than 5 wt% of N to prevent the introduction of ohmic drops associated with the transport of electrons in the system. The SNCs are stabilized on the EC surface by means of strong interactions with: (i) defects of the graphene nanoplatelets; and (ii) C- and N-based ligands of the CN “shell”, making up the “coordination nests”. As a result, the low-Pt described here exhibit an outstanding durability. This work takes into consideration the various families of low-Pt ECs based on H-GR supports developed so far by our group, and discusses extensively the interplay between: (i) the preparation parameters (e.g., synthesis of the support, chemical/electrochemical activation steps) [10]; (ii) the physicochemical properties (e.g., chemical composition, morphology, structure); (iii) the electrochemical behavior (e.g., intrinsic activity and ORR reaction mechanism); and (iv) the performance in a single PEMFC tested under operating conditions. Finally, the results are compared with the state of the art and new research avenues are suggested. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD. Figure 1

A series of samples are collected from the catholyte solution of a vanadium redox flow battery (VRFB) at different values of state of charge (SoC)/state of discharge (SoD). The samples are analyzed by means of Raman spectroscopy to identify: (i) the species present into the catholyte; and (ii) how the composition of the catholyte is modulated along the charge and discharge processes of the VRFB. Raman results reveal that the most abundant species in the catholye are VO2+ and VO2+; they are coordinated by HSO4− and SO42− ligands. During the charge process of the VRFB the equilibrium between the vanadium species is shifted towards the formation of an ensemble of V(V) complexes. Instead, during discharge a family of V(IV) species is obtained. The formation of concatenated HV2O5− and H3V2O7− species in the catholyte is revealed, which indicates that side electrochemical reactions occur during the charge and discharge processes of a VRFB. The presence of these side reactions plays a crucial role in the modulation of the Coulombic efficiency of the VRFB. This work highlights the complexity of the chemical situation at a VRFB cathode, and the great importance to understand/control such chemical situation to improve the performance of VRFBs in the scenario of electrochemical energy storage field.

The paradigm shift in today’s energy harnessing, distribution and utilization is leading to massive investments in innovative technologies, that include electrochemical energy conversion and storage systems (EECS) [1, 2]. The latter exhibit a number of very attractive features, that include negligible emissions of greenhouse gases at the point of operation, a facile scalability and the independence from geographical constrains. Furthermore, EECS are typically characterized by a very high efficiency, as they are not constrained by the limits associated to Carnot’s engines [3]. A broad range of EECS are available, each well-suited for a particular family of applications. In this panorama, the incidence and relevance of proton-exchange membrane fuel cells (PEMFCs) is progressively rising. State-of-the-art PEMFCs have exited the research laboratories and are currently implemented in early products, that include both stationary systems (e.g., power plants for “zero-emission” houses) and light-duty vehicles. Despite these successes, PEMFCs still suffer from several drawbacks. In particular: (i) the performance and the durability of the functional materials involved in PEMFC operation must be increased to match the requirements set by the applications; and (ii) at the same time, the costs must be curtailed to warrant a large-scale market penetration of PEMFCs and leverage the latter’s advantages over competing traditional technologies. One key issue affecting both development areas is the electrocatalyst (EC) that promotes the oxygen reduction reaction (ORR) at the PEMFC cathode. Indeed, to bestow the PEMFC a sufficient performance and durability, state-of-the-art ECs for the ORR must include a very high loading of platinum. Thus, to mitigate the risk to incur in supply bottlenecks [4], new and improved ECs with a low-loading of Pt (“low-Pt”) must be developed. An innovative approach to obtain advanced low-Pt ECs for the ORR exhibiting a performance and durability beyond the state of the art is to devise systems where the active sites are located on the surface of PtMx sub-nanometric clusters (SNCs). PtMx are alloys between Pt and a first-row transition metal (e.g., Ni, Cu), that acts as a “co-catalyst” and promotes the intrinsic ORR kinetics reaching levels that are well beyond the Pt baseline [5]. SNCs offer important advantages over the Pt nanoparticles (NPs) used in conventional ECs for the ORR. In particular, with respect to Pt NPs, in SNCs the utilization of Pt atoms is raised by up to ca. one order of magnitude. This allows for the maximization of the Pt availability for electrocatalytic purposes. Hence, the PEMFCs mounting the low-Pt ECs comprising the SNCs can achieve a specific power that is significantly larger than the 8 kW/gPt target set by the DoE for 2020 [6]. In the proposed ECs the SNCs are located on the surface of a support that exhibits unique features. In detail, the support is based on a “core” consisting of a combination of highly defected graphene nanoplatelets and carbon black NPs [7]. Such hierarchical graphene-based (H-GR) “core” is covered by a carbon nitride (CN) “shell”, that is able to stabilize effectively the SNCs by means of “coordination nests” consisting of C- and N- ligands. The present contribution compares the proposed low-Pt ECs with the state of the art and overviews the complex correlations that are established between: the physicochemical properties of the low-Pt ECs (e.g., chemical composition, morphology and structure of both the active sites and of the support); the electrochemical performance, the reaction mechanism and the durability in the ORR; and finally the characteristic curve of the PEMFC mounting the proposed ECs as tested in operating conditions. The information thus obtained is then used to identify the most promising research approaches to pursue in order to devise next-generation low-Pt ORR ECs able to comply with the stringent requirements of tomorrow’s PEMFCs. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD. Figure 1

One of the most relevant factors limiting the performance of proton-exchange membrane fuel cells (PEMFCs) is the large cathode overpotential, that is associated to the sluggishness of the oxygen reduction reaction (ORR) in an acidic environment. In conventional state-of-the-art PEMFCs the ORR is promoted by electrocatalysts (ECs) that include a very high loading of platinum-group metals in order to achieve performance and durability levels that are matching the requirements set by the applications. Indeed, Pt is the element that affords the best ORR kinetics in an acidic environment. This is a major shortcoming of today’s PEMFCs, whose large-scale rollout is hindered by the significant risk to incur in Pt supply bottlenecks [1]. This issue is addressed by developing ORR ECs that do not include platinum (“Pt-free” ECs). It is shown that the ORR can be effectively promoted by active sites that are based on a first-row transition metal (e.g., Fe, Co and Ni), that is bound on the surface of the EC by coordination interactions mediated by C and N ligand atoms. It is also revealed that the EC performance is raised significantly by the addition of another element (e.g., Sn) that acts as a “co-catalyst”. The ORR kinetics of such “Pt-free” ECs improves dramatically in an alkaline environment, where the adsorption of O2 on the active sites is more facile. Finally, the performance and the durability of the “Pt-free” ECs are strongly affected by the chemical composition, structure and morphology of the support, that must minimize the ohmic drops and facilitate the mass transport phenomena. In this framework, in principle graphene is a very attractive support for ORR ECs as it affords: (i) a very high specific area; (ii) an outstanding electron mobility; and (iii) a negligible microporosity. Hence, graphene is adopted as the main component of the support included in a several different families of “Pt-free” ORR ECs, whose development is overviewed in this work. All the ECs described here are obtained with the synthetic protocol devised in our laboratory [2], and are characterized by a “core-shell” morphology. In detail, the graphene-based support “core” is covered by a carbon nitride “shell”, that stabilizes the active sites in “coordination nests” based on C- and N- ligands. The physicochemical properties of the proposed ECs (e.g., chemical composition, morphology, porosity and structure) are correlated with the ORR performance determined both in “ex-situ” measurements carried out in half-cell configuration and in single fuel cell tested under operating conditions. It is elucidated the impact of: (i) the chemical composition of the active sites; (ii) the features of the support (e.g., size of graphene sheets, presence of spacers); and (iii) the details of the post-synthesis treatments carried out on the ECs on the ORR overpotentials and reaction pathway as a function of the pH of the environment. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD. References [1] R.L. Moss, E. Tzimas, P. Willis, J. Arendorf, L. Tercero Espinoza, Critical Metals in the Path towards the Decarbonisation of the EU Energy Sector – Assessing Rare Metals as Supply-chain Bottlenecks in Low-carbon Energy Technologies, Publications Office of the European Union, Luxembourg (2013). [2] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, 59 (2015).

This work reports two quasi-solid composite electrolytes based on LiFT (Lithiated Fluorinated Titania) nanopowder and either 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) ionic liquid (IL). In details, LiFT nanopowder is doped with ca. 30 wt% of IL, giving rise to materials with formula LiFT/(EMImBF(4))(0.)(183) and LiFT/(EMImTESI)(0.)(087). The resulting composite electrolytes appear as powder-like solids as the IL is completely absorbed by LiFT. The correlation between structure, thermal properties and long-range charge migration processes of the here proposed electrolytes is investigated by several characterization techniques, as follows: i) differential scanning calorimetry (DSC) and high-resolution thermog-ravimetry (HR-TGA); ii) Fourier-transform infrared spectroscopy in both the medium and the far infrared (FT-MIR and FT-FIR); and iii) broadband electrical spectroscopy (BES). The conductivity of the here proposed composite electrolytes is promising. Indeed, at 30 and 100 degrees C it corresponds respectively to 1.75 x 10(-3) S cm(-1) and 1.05 x 10(-2) S cm(-1) for LiFT/(EMImBF(4))(0.183), and 1.36 x 10(-2) S cm(-1) and 4.42 x 10(-2) S cm(-1) for LiFT/(EMIMITSI)(0.087). Finally, LiFT/(EMImTESI)(0.087) is used to fabricate a coin cell prototype, that is tested by galvanostatic cycling for performance and durability. (C) 2019 Elsevier Ltd. All rights reserved.

Electrochemical energy conversion and storage (EECS) systems are of major interest for both industry and the scientific community owing to their potential to fulfill a major role in today’s worldwide efforts to decarbonize the energy sector. Indeed, EECS systems exhibit a very high energy conversion efficiency, are easy to scale-up and they are not affected by geographical constrains [1]. Two families of EECS are attracting particular attention owing to the complementarity of their applications, namely ion-exchange membrane fuel cells and redox flow batteries. On one hand, ion-exchange membrane fuel cells are particularly suited for light-duty vehicles and small-scale stationary systems (e.g., auxiliary power units) owing to their high energy and power densities [2]. On the other hand, redox flow batteries (with a particular reference to all-vanadium redox flow batteries, VRFBs) are ideally suited to the large-scale storage of energy for the power grid as they are characterized by a very high turnover efficiency and an outstanding cyclability [3]. Electrolyte membranes (EMs) are found at the core of both ion-exchange membrane fuel cells and VRFBs. The role of such EMs is to: (i) keep separated the electroactive species involved in the redox reactions taking place at the electrodes and, at the same time, (ii) ensure a facile and selective migration of ions to prevent the polarization of the device and allow for the establishment of large current densities. As of today, the most widely adopted EMs for both ion-exchange membrane fuel cells and VRFBs are based on perfluorinated ionomers such as Nafion™ and other similar macromolecules [3, 4]. These systems exhibit an outstanding proton conductivity and a very high chemical and electrochemical stability; however, they also suffer from important drawbacks such as: (i) a dramatic drop in conductivity at T > 80°C and in dry conditions; (ii) poor mechanical properties; and (iii) a large permeability to vanadium species [5]. Consequently, it is often necessary to: (i) add humidification modules to ion-exchange membrane fuel cells, thus raising the bulk and cost of the device; or (ii) especially in the case of VRFBs, use thick EMs that curtail the current density. These drawbacks can be addressed by implementing several different strategies, that include: (i) the introduction of a filler in the EM, giving so rise to a hybrid inorganic-organic membrane [6]; (ii) the fabrication of the EM with a different macromolecule (e.g., a sulfonated polyaromatic system such as sulfonated polyether ether ketone, SPEEK [7], or innovative anion-exchange polymers [8]); and (iii) the doping of the EM with an ion-conducting medium (e.g., phosphoric acid [9], or a proton-conducting ionic liquid [10]). All of these strategies operate by modulating the physicochemical properties of the EMs, with a particular reference to the details of the phase segregation at the nano/mesoscale [4]. This work overviews the study of the interplay between the physicochemical properties of hybrid ion-exchange membranes (with a particular reference to the chemical composition, thermoanalytical properties, morphology and structure), and the electrical response as determined by means of advanced investigation techniques such as Broadband Electrical Spectroscopy (BES). Results allow to: (i) elucidate the interactions between the different phases and components within each EM; and (ii) clarify the conductivity mechanism. On these bases, it is possible to identify the most promising avenues of research to devise EMs for application in ion-exchange membrane fuel cells and redox flow batteries exhibiting a performance and a cyclability beyond the state of the art. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD. Figure 1

The sluggishness of the kinetics of the oxygen reduction reaction (ORR) is one of the most relevant phenomena curtailing the operation capability of proton-exchange membrane fuel cells (PEMFCs)[1]. Hence, the development of advanced ORR electrocatalysts (ECs) is one of the main goals of the research in this field. The ECs described here exhibit a “core-shell” morphology: a hierarchical graphene-based support (H-GR) “core” is covered by a carbon nitride “shell” stabilizing the active sites in “coordination nests” [2]. The “core” comprises highly defected graphene nanoplatelets [3] and carbon black nanoparticles; the latter act as spacers and facilitate the charge and mass transport phenomena that take place during the EC operation. The ECs proposed here are characterized by a very low loading of platinum, on the order of ca. 5 wt%, that is the “active metal”; Ni is introduced as the “co-catalysts” to improve the ORR performance [2]. An extensive post-synthesis activation process (A) is applied to the ECs, significantly affecting their chemical composition, structure and morphology. The ORR performance of the “activated” ECs is much improved in comparison with state-of-the-art Pt/C reference ECs. This work is aimed at investigating the effect of different activation parameters on the ORR performance and reaction mechanism, aiming at a robust and reliable upscaling of the preparation process [4]. The proposed ECs are extensively characterized both before and after A to study the complex interplay between the synthetic/activation parameters, the physicochemical properties, and the electrochemical ORR performance both “ex-situ” and in single PEMFC. The bulk chemical composition of the ECs is determined by means of Inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and CHNOS microanalyses; the structure is investigated through wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies (e.g., confocal micro-Raman); the surface composition and oxidation states are probed with X-ray photoelectron spectroscopy (XPS); morphology is observed by high-resolution transmission electron microscopy (HR-TEM); the details of the ORR performance and reaction pathway as a function of the pH of the environment are elucidated by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE). Finally, the ECs are used to fabricate membrane-electrode assemblies (MEAs) that are tested in single PEMFC in operating conditions. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219, and from the BIRD 2018 program of UNIPD. References [1] I. Katsounaros, S. Cherevko, A. R. Zeradjanin, K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 53, 102 (2014). [2] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, (2015) 59-64. [3] V. Di Noto, E. Negro, A. Bach Delpeuch, F. Bertasi, G. Pagot, K. Vezzù, Patent application PCT/EP2017/084801 (2017). [4] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, L. Toncelli, S. Zeggio, F. Bassetto, Patent application PCT/IB2016/055728 (2016).

Nafion-tungsten oxide hybrid membranes, [Nafion/(WO3)(x)], with varying loading levels of WO3 nanofiller (x = 0, 0.024, 0.329) are prepared and investigated as candidates for application as solid electrolytes in vanadium redox flow batteries (VRFBs). The thermal properties of [Nafion/(WO3)(x)] hybrid membranes are probed both by high-resolution thermogravimetric analysis (HR-TGA) and by modulated differential scanning calorimetry (MDSC). Vibrational spectroscopy studies are carried out by: (i) Attenuated Total Reflectance - Fourier Transform Infrared spectroscopy (ATR-FTIR); and (ii) Raman spectroscopy, to elucidate the secondary structure of [Nafion/(WO3)(x)]J and study the interactions taking place between the nanofiller and the Nafion matrix. The electrical response of [Nafion/(WO3)(x)]J is determined by Broadband Electrical Spectroscopy (BES) and the permeability towards VO2+ is measured by UV-VIS spectrometry. It is demonstrated that the [Nafion/(WO3)(x)] hybrid membranes exhibit a high ion selectivity (up to 10.6.10(3) S.min-cm(-2) for [Nafion/(WO3)(0.329)]) that is much improved in comparison with that characterizing recast Nafion (6.5-10(3) S.min.cm(-3)). A structural model and a conductivity mechanism for the [Nafion/(WO3)(x)] hybrid membranes are proposed, in order to rationalize the experimental results and correlate the electrical response with the transport properties.

The electrical response of zirconia composite polybenzimidazole membranes [PBI4N(ZrO2)(x)](H3PO4)(y) is studied by Broadband Electrical Spectroscopy (BES), and correlated with our previous Dynamic Mechanical Analysis (DMA) and Modulated Differential Scanning Calorimetry (MDSC) measurements. The presence of nanofiller in the PBI4N polymer matrix is shown to plasticize the membrane, with a maximum effect observed at a nanofiller loading level of x approximate to 0.13. The disrupting effect of the nanofiller on the interchain dipole interactions modulates the overall electrical response of the materials. Following acid doping, a marked increase in conductivity is observed as new chemistry is installed at the interfaces between polymer and nanofiller that facilitates dipolar fluctuations and segmental motions of the polymer chains. In these composite membranes, two mechanisms of conductivity are postulated based on BES analysis; i) proton hopping between binding sites, and ii) proton hopping at the interfaces between H(n)PHI4N(n+)/H(n)PBI4N(n+) and H(n)PHI4N(n+)/HmZrO2m+. The results here presented demonstrate the effect of zirconia nanofiller and subsequent acid doping on the conductivity properties of composite PBI4N membranes. Of note, at 100 degrees C for [PBI4N(ZrO2)(0.132)](H3PO4)(11), conductivity as high as 0.035 S/cm is achieved.

The intrinsic sluggishness of the oxygen reduction reaction (ORR) is a major bottleneck in the operation of low-temperature fuel cells. This issue is particularly relevant for proton-exchange membrane fuel cells (PEMFCs). In these systems the electrodes operate in a strongly acid environment, where the best performance is afforded by active sites based on platinum-group elements (PGMs). Accordingly, owing to the extremely low abundance of PGMs in Earth’s crust, the development of ORR electrocatalysts (ECs) comprising a minimized loading of PGMs is a major goal of both fundamental and applied research to achieve a widespread rollout of PEMFC technology. One of the best strategies to obtain high-performing ORR ECs with a minimized loading of PGMs is to devise nanocomposite systems, comprising: (i) support materials with a high electrical conductivity and large surface area (e.g., carbon black or carbon nanotubes); and (ii) PGM-based nanostructures (e.g., nanoparticles, nanowires, and nanocages) exhibiting a large specific area. This approach allows to maximize the utilization of PGM atoms and boost the EC performance. The intrinsic performance of the active sites in the ORR can be further raised by introducing in the EC suitable “co-catalysts”, typically first-row transition metals (e.g., Fe, Co, Ni, Cu). This work reports a new family of ECs with a low loading of PGMs (L-PGM) for the ORR. The ECs exhibit a “core-shell” morphology. A hierarchical graphene-based support (H-GR) “core” is covered by a carbon nitride (CN) “shell” stabilizing Pt-based nanostructures in “coordination nests” [1]. Two main components are comprised in the “core”, namely: (i) highly defected graphene nanoplatelets, that are supported on ZnO nanoparticles (NPs) [2]; and (ii) carbon black NPs, whose introduction facilitates the charge and mass transport phenomena. The CN “shell” binds the Pt-based nanostructures bearing the ORR active sites. The latter include two “co-catalysts”, i.e., Ni and Cu. This work studies the interplay between: (i) the relative stoichiometry of the Ni and Cu “co-catalysts”; and (ii) the physicochemical properties and the electrochemical performance of the ECs, as determined both “ex-situ” and in an operating PEMFC. The ECs undergo extensive characterization studies aimed at the elucidation of the chemical composition, morphology, structure, and porosity features of the ECs. Particular efforts are dedicated to study the impact of the “post-synthesis” activation steps that are necessary to maximize the performance of the ECs [3]. The cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE) technique is adopted to study: (i) the ORR kinetics and reaction mechanism, by means of the Tafel analysis; (ii) the average number of electrons exchanged during the ORR, in order to determine the selectivity in the reduction of O2 to water. Finally, the most promising ECs are studied in single PEMFC running in operating conditions, with the purpose to: (i) optimize the electrode configurations and the compatibility with the proton-conducting membrane; and (ii) study the interplay between the physicochemical properties of the ECs (e.g., the morphology) and the PEMFC performance. Acknowledgement This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 785219 of the Graphene Flagship, and from the BIRD 2016 program of UNIPD. References [1] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, (2015) 59-64. [2] V. Di Noto, E. Negro, A. Bach Delpeuch, F. Bertasi, G. Pagot, K. Vezzù, Patent application 102017000000211 (2017). [3] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, L. Toncelli, S. Zeggio, F. Bassetto, Patent application PCT/IB2016/055728 (2017).

In this study, a new family of poly(vinyl alcohol)-based solid membrane electrolytes is proposed. The single ion conducting polyelectrolytes are obtained by direct lithiation of partially hydrolyzed poly(vinyl alcohol), forming a lithium-poly(vinyl alkoxide) macromolecular salt. Furthermore, in order to improve the ionic conductivity, the obtained polymer is plasticized with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) ionic liquid. Thermogravimetric analysis demonstrates a thermal stability higher than 215 degrees C. Differential Scanning Calorimetry studies show a polymer associated glass transition event and a melting transition related to the ionic liquid domains at ca. +80 and -40 degrees C respectively. Fourier-transform infrared spectroscopy proves that: a) lithiation of the membrane results in an increase to the amorphic character of the polymer backbone; and b) after ionic liquid addition to the lithiated membrane, the effective coordination of lithium cations by the TFSI-anions of the ionic liquid augments the ionic conductivity of the proposed materials. Broadband electrical spectroscopy (BES) investigations reveal that this system is characterized by several polarization phenomena and dielectric relaxation events. Analysis of the DES results, using suitable models, allows for the conductivity mechanism in the proposed polymer electrolytes to be hypothesized. Finally, the ionic conductivity values of 1.29 . 10(-5) S cm(-1) and 1.92.10(-3) S cm(-1) at 30 and 80 degrees C render these materials very promising for application in electrochemical devices.

In this study, a new family of electrocatalysts (ECs) for the oxygen reduction reaction (ORR) is presented. The ECs, that exhibit a “core-shell” morphology, include: (i) a hierarchical graphene-based support (H-GR) “core” , that is covered by: (ii) a carbon nitride “shell” stabilizing the active sites in “coordination nests” [1]. The H-GR comprise two main components, namely: (i) ZnO nanoparticles supporting highly defected graphene nanoplatelets [2]; and (ii) carbon black nanoparticles; the latter improve the charge and mass transport phenomena associated to EC operation. The active sites of the ECs do not include platinum-group metals (PGMs); instead, they are based on Fe (playing the role of “active metal” ) and also contain Sn as the “co-catalyst” [1]. The synthetic route that is pursued to obtain the proposed ECs consists in the following main steps: (i) preparation of a precursor comprising the H-GR support; and (ii) multi-step pyrolysis process yielding the carbon nitride “shell” and the active sites [1]. In this study, other treatments are introduced in the synthetic route ( e.g. , chemical etching; electrochemical cycling; and/or further pyrolysis steps), with the purpose of fine-tuning the morphology, pore structure, and chemical composition of the ECs and thus maximize the performance in the ORR. The ECs obtained in this study undergo an extensive characterization campaign, with the aim of elucidating the details of the interplay between the parameters of the synthetic route, the physicochemical features and the electrochemical performance and durability. In particular, the role of the various components included in the H-GR support ( i.e. , the highly defected graphene nanoplatelets, the ZnO and the carbon black nanoparticles) is studied accurately, striving to discern the impact of each in the properties of the final ECs. The bulk chemical composition of the samples is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and CHNOS microanalysis. X-ray photoelectron spectroscopy is adopted to probe the chemical composition and the oxidation states of the elements on the surface of the ECs. The structure of the samples is studied by means of vibrational spectroscopies ( e.g. , confocal micro-Raman) and wide-angle X-ray diffraction (WAXD). The morphology and pore structure of the samples is investigated by means of high-resolution transmission electron microscopy (HR-TEM) and nitrogen physisorption techniques. The performance, reaction mechanism and durability of the ECs in the ORR is studied through the CV-TF-RRDE technique (cyclic voltammetry with the thin-film rotating ring-disk electrode). Finally, the interplay between the ORR kinetics and the chemical composition of the active sites is clarified by studying the ORR mechanism at different pH values. Acknowledgements This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 696656. The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence). References [1] V. Di Noto, E. Negro, K. Vezzù, F. Bertasi, G. Nawn, The Electrochemical Society Interface, Summer 2015, (2015) 59-64. [2] V. Di Noto, E. Negro, A. Bach Delpeuch, F. Bertasi, G. Pagot, K. Vezzù, Patent application 102017000000211 (2017).

Ionic liquids (ILs) have drawn sustained attention in the last twenty years due to their unique combination of intrinsic conductivity, very low vapour pressure and their ability to be tailored to an application via facile chemical modification [1]. As a consequence, the development of new ILs with improved properties and an in-depth understanding of the interplay existing between structures and properties are particularly active research fields. In this report preparation and study of a new lipophilic tetraoctyl-formamidinium bis(trifluoromethanesulfonyl) imide (TOFATFSI) ionic liquid [2], will be discussed. Tetraoctyl-formamidinium (TOFA) TFSI proved to be a water-insoluble IL that is completely miscible with the lower alkanes and the solutions are ionic conductors. Therefore, we were intrigued if conductivity could be induced in an even more demanding medium, i.e. supercritical carbon dioxide (scCO2) [3,4]. Following this, the conductivity and relaxation phenomena of this new IL are revealed through the analysis of the broadband electric spectra with a particular emphasis on the effect of temperature and CO2 pressure on the IL conductivity. It is found that temperature boosts the conductivity via an increase in the charge carrier mobility. Also, CO2 absorption affects both the conductivity and the permittivity of the material due to the presence of CO2–IL interactions that modulate the nanostructure and the size of the TOFATFSI aggregates, which increases both the mobility and the density of the charge carriers. Acknowledgements The authors wish to thank the Strategic Project of the University of Padova “Materials for Membrane-Electrode Assemblies to Electric Energy Conversion and Storage Devices (MAESTRA)” for funding. V.D.N. thanks the University Carlo III of Madrid for granting him the “Catedra de Excelentia” (Chair of Excellence). References [1] F. Bertasi, K. Vezzù, G. Nawn, G. Pagot, V. Di Noto, Interplay Between Structure and Conductivity in 1-Ethyl-3-methylimidazolium tetrafluoroborate/(δ-MgCl2)f Electrolytes for Magnesium Batteries, Electroch. Acta, 219, 152-162 (2016). [2] Federico Bertasi, Guinevere A. Giffin, Keti Vezzù, Pace Giuseppe, Yaser Abu-Lebdeh, Michel Armand, Vito Di Noto, A lipophilic ionic liquid based on formamidinium cations and TFSI: The electric response and the effect of CO2 on conductivity mechanism, PCCP, 19, 26230 – 26239 (2017). [3] V. Di Noto, K. Vezzù, F. Conti, G.A. Giffin, S. Lavina, A. Bertucco. Broadband electric spectroscopy at high CO2 pressure: Dipole moment of CO2 and relaxation phenomena of the CO2 - poly(vinyl chloride) system. J. Phys. Chem. B, 115, 9014-9021 (2011). [4] S. Kitajima, F. Bertasi, K. Vezzu’, E. Negro, Y. Tominaga, V. Di Noto. Dielectric relaxations and conduction mechanisms in polyether-clay composite polymer electrolytes under high carbon dioxide pressure. Phys. Chem. Chem. Phys., 15, 16626-16633 (2013). Figure 1

The numerous potential benefits of incorporating anion-exchange membranes (AEMs), in place of proton-exchange membranes (PEMs), in energy storage and conversion technologies renders their development of fundamental importance for the continued evolution of alternative energy systems. However, the widespread implementation of AEMs is currently plagued by a range of problems including lower conductivity (with respect to PEMs), poor stability, and high cost. This study reports the conversion of polyketone, one of the world's most mass produced and cheap polymers, to a new highly tuneable polymer architecture, functionalized polyketone (FPK), that demonstrates a range of excellent properties rendering it a significant prospect for AEM materials. The thermal, processing, and ion-conducting properties of FPK are governed by the amount and nature of the newly formed N-substituted pyrrole pendant side groups. At 80 degrees C, the quarternized pyridyl FPK derivative (4MPyrFPK) yields ion-conductivities of 8.6 and 10.5 mS cm(-1) in the iodide and hydroxide forms. In addition, the hydroxide form of 4MPyr-FPK demonstrates remarkable stability toward the typically problematic alkaline conditions. No chemical decomposition is observed to the membrane after imbibing it in KOH solution for 72 h, and furthermore, the ion-conductivity is demonstrated to remain constant for at least 30 d at 80 degrees C.