In chemical catalysis, understanding bond formation and cleavage processes is essential. In this study, core–shell electrocatalysts for proton exchange membrane fuel cells (PEMFCs) are investigated, with particular emphasis on the qualitative and quantitative characterization of their surface morphology. The chemical and physical properties of the electrocatalysts are evaluated through adsorption-based methods. N₂ physisorption is employed to determine the specific surface area (S, m²⋅g⁻¹) and to analyze micro- and mesoporosity using established mathematical models. Water adsorption measurements are conducted to assess the hydrophilic/hydrophobic behavior of the materials. Furthermore, by determining the real density of the electrocatalysts, the surface area per volume (Σ, m²⋅cc-1) parameter was calculated, which is particularly useful for the design of efficient membrane electrode assemblies (MEAs). The combined morphological (surface area and porosity) and compositional analyses (CHNS, XPS, and EDX) enable the establishment of correlations with ex situ electrocatalytic performance, as evaluated by rotating ring–disk electrode (RRDE) measurements.

The large-scale deployment of decarbonized hydrogen-based energy systems critically depends on the availability of large amounts of sustainable and low-cost “green hydrogen” produced without emissions of greenhouse gases. In this context, water electrolysis powered by renewable electricity represents a key enabling technology. Among emerging electrolyzer concepts, anion-exchange membrane water electrolyzers (AEMWEs) have recently attracted considerable scientific and technological interest. This growing attention stems from the unique position of AEMWEs, which combine the most advantageous features of other established electrolyzer families. Similar to proton-exchange membrane water electrolyzers (PEMWEs), AEMWEs exhibit a compact architecture and enable operation at high current and power densities. At the same time, their alkaline operating environment allows the use of electrocatalysts (ECs) that do not comprise platinum-group metals (PGMs), as in conventional alkaline electrolyzers, thus reducing reliance on critical raw materials. This contribution overviews two representative classes of oxygen evolution reaction (OER) ECs specifically developed for operation under alkaline conditions. The first class comprises spinel-type oxides, differentiated by the nature of the constituent metal cations and their distribution within the oxygen lattice. The second class includes multimetallic oxide systems synthesized via electrodeposition onto electrically-conductive substrates. All the ECs undergo a comprehensive physicochemical and electrochemical characterization, aimed at assessing bulk and surface composition, crystalline structure and phase distribution, morphological features, as well as OER activity and mechanistic aspects. The study primarily focuses on establishing correlations between synthesis parameters, intrinsic physicochemical properties, and electrochemical performance. In addition, the evolution of EC composition, structure, and morphology upon operation at the anode of a single-cell AEMWE is investigated. The combined insights are used to derive design principles for the development of next-generation PGM-free OER ECs suitable for alkaline electrolysis. Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels” ]; (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; (c) the project AMBITION financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; and (d) the project DURALYS funded by the the Italian Ministry of Foreign Affairs and International Cooperation (MAECI).

The practical implementation of the hydrogen economy on a large scale is still bottlenecked by the properties of proton-exchange membrane fuel cells (PEMFCs). The latter proved highly suitable for a variety of applications, both stationary and in the mobility sector, owing to their high energy conversion efficiency and remarkable power density. Despite decades of intensive research PEMFCs still require a significant loading of critical raw materials (CRMs), with a particular reference to platinum group metals (PGMs), to achieve the performance and especially the durability levels required by the applications. This work is focused on elucidating the interplay between the physicochemical features and the electrochemical performance of “core-shell” electrocatalysts (ECs) for the oxygen reduction reaction (ORR). The ORR ECs consist of a carbonaceous “core” covered by a carbon nitride (CN) “shell” coordinating PtNi x nanoparticles. The latter bear the active sites for the ORR. The CN “shell” of the proposed ECs includes less than 5 wt% of N to minimize the ohmic losses; Pt acts as the “catalyst” , providing most of the ORR performance; Ni acts as the “co-catalyst” , raising the performance of the “catalyst” [1]. The proposed ECs are obtained by a multi-step process, consisting of: (i) preparation of a Z-IOPE precursor, wherein Pt and Ni are bridged by cyano ligands; (ii) pyrolysis of the precursor; and (iii) final post-synthesis activation treatments to etch the labile synthesis byproducts [1]. This work investigates how activation and ageing affect the physicochemical features of the proposed ORR ECs. The latter undergo activation and accelerated chemical/electrochemical “ex-situ” ageing before going through an extensive characterization campaign. The chemical composition, morphology, structure and electrochemical properties are investigated as a function of activation and ageing. State-of-the-art techniques are implemented, including x-ray fluorescence (EDX), high-resolution transmission electron microscopy (HR-TEM), near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), X-ray absorption spectroscopy (XAS) and cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE). The resulting information is expected to shed light on how to develop ORR ECs beyond the state of the art and exhibiting an enhanced performance and durability. References [1] V. Di Noto et al. , ACS Catalysis, 12, 12291−12301 (2022). Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels”]; (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; (c) the project AMBITION financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; (d) the project DURALYS funded by the Italian Ministry of Foreign Affairs and International Cooperation (MAECI); and (e) project GreenHyFlex, #25700_006808 funded by Regione Veneto

One of the main stepping stones towards the practical implementation of the “hydrogen economy” is the availability of abundant and inexpensive hydrogen obtained without releasing massive amounts of greenhouse gases ( e.g. , CO 2 ) in the atmosphere. The most promising avenue to achieve this goal is to produce “green hydrogen” by water electrolysis. Recently, significant attention has been drawn by the development of the first effective anion-exchange membrane water electrolyzers (AEMWEs). The heart of such devices consists of membrane-electrode assemblies (MEAs) wherein an anion-exchange membrane (AEM) is sandwiched between two electrodes, each promoting either the hydrogen evolution reaction (HER) or the oxygen evolution reaction (OER). A very attractive feature of AEMWEs is that they operate in an alkaline environment. Hence, it is possible to devise very high-performing HER and OER electrodes for implementation in AEMWEs that do not include critical raw materials (CRMs), with a particular reference to platinum-group metals (PGMs). This work proposes a very straightforward approach to prepare complete, high-performance and completely “PGM-free” OER electrodes for application in AEMWEs. The electrodes are obtained by electrodeposition and undergo a comprehensive physicochemical and electrochemical characterization both before and after operation at the anode of a single-cell AEMWE. This allows to clarify the complex interplay between: (i) the synthetic parameters; (ii) the features of the electrodes; and (iii) how the latter are affected by the harsh conditions (especially in terms of alkaline pH and high current density) occurring at the anode of an AEMWE. The chemical composition of the electrodes is determined both in the bulk (by x-ray fluorescence, EDX) and on the surface (by near-ambient pressure X-ray photoelectron spectroscopy, NAP-XPS). The porosimetric features are studied by nitrogen physisorption; the morphology is probed by ultra-high resolution scanning electron microscopy (UHR-SEM), while the structure is investigated by wide-angle X-ray diffraction (WAXD) and vibrational spectroscopies ( e.g. , micro-Raman). The electrochemical performance of the electrodes is studied both “ex-situ” in a three-electrode configuration and in a complete single-cell AEMWE run in operating conditions. Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels” ]; (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; (c) the project AMBITION financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; and (d) the project DURALYS funded by the Italian Ministry of Foreign Affairs and International Cooperation (MAECI).

Sodium solid electrolytes combining high ionic conductivity, interfacial stability and long-term durability enable reliable all-solid-state sodium batteries, a promising alternative to lithium-based systems. This work presents a comparative study of three representative families of solid electrolytes: NASICON-type ceramics, cross-linked polymer electrolytes and hybrid polymer-in-ceramic systems obtained via in-situ cross-linking within porous ceramic matrices.Structural and morphological analyses reveal that dense NASICON electrolytes favor bulk Na⁺ transport, whereas cross-linked polymer electrolytes form amorphous networks with homogeneous composition. Hybrid electrolytes successfully integrate both phases, yielding improved interfacial contact and structural integrity and handling stability. Thermal characterization shows excellent stability for NASICON, delayed degradation for polymer electrolytes due to cross-linking, and significantly enhanced thermal stability for hybrids (>370 °C), attributed to strong organic-inorganic interactions. Broadband Electric Spectroscopy (0.03–107 Hz; −100 to +150 °C) clarifies conduction mechanisms, where Vogel-Tamman-Fulcher behavior confirms coupling between ion transport and matrix dynamics. Na⁺ migration distances increase with temperature, reaching ∼4 nm (NASICON), ∼10 nm (NPC1000-NaX), and up to 100 nm (HSE-NaX). Favorable interdomain pathways and ClO4⁻ anions enhance structural–dynamic coupling and long-range sodium transport in hybrids. Electrochemical cycling in Na/FePO₄ cells reveals a balance between initial capacity and durability. NASICON displays modest initial capacity (∼85 mAh·g⁻¹) but progressive increases to ∼113 mAh·g⁻¹ after 500 cycles (∼96 % retention), whereas polymer and hybrid electrolytes deliver higher initial capacities (>100 mAh·g⁻¹) but experience capacity decay during prolonged cycling. In summary, NASICON-type electrolytes offer superior long-term durability and stability, whereas polymeric and hybrid systems favor higher initial performance, revealing a trade-off governed by electrolyte architecture.

Electrolyte systems based on the short chain block copolymer (BCP) of poly(ethylene oxide)-b-polyethylene, PEO-b-PE, doped with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide ([EMIM][TFSI]) and monovalent cation salts (MTFSI) were examined. Samples were prepared with the ratio of [IL]/[EO] equal to 0.04 and the r = [M+]/[EO] = 0.02 and 0.04. The interplay between ion coordination, polymer dynamics, and conductivity were elucidated. Small- and wide-angle X-ray scattering results highlighted the effect of metal cations on the decreasing d-spacing as well as increasing anion-anion distance, emphasizing the interactions between the cations with the PEO chains and their role as physical junctions. The interactions also make the chains more packed, destroy the crystalline structure of PEO, and increase the viscosity. The coordination of the oxygen atoms of PEO with the cations hinders the chain mobility. Broadband electric spectroscopy (BES) results suggest that Li+ and Na+ electrolytes exhibit a higher density of dynamic cross-links than K+ electrolytes. To clarify how polymer matrix relaxation dynamics correlate with long-range cation migration, we applied the Walden rule. Electrolytes show deviations from ideal conditions of perfect coupling between polymer matrix relaxation dynamics and long-range ionic migration. For K+ at r = 0.02 and 0.04, Li+ at r = 0.02, and Na+ and at r = 0.04 electrolytes, polymer relaxation dynamics are more hindered than ionic migration processes. In contrast, Li+ at r = 0.04 and Na+ and at r = 0.02 electrolytes have more hindered long-range ionic migration than matrix relaxation phenomena.

Developing cost-effective materials for electrocatalytic water splitting is essential for clean hydrogen production and making it competitive with other hydrogen produced by carbon-footprint fossil fuels. In anion exchange membrane water electrolysis (AEMWE), achieving both high efficiency and long-term durability is essential to enable economically viable and scalable hydrogen production. High efficiency reduces the energy input required for hydrogen generation, directly impacting operating costs and sustainability, while durability ensures stable performance under harsh alkaline conditions, minimizing degradation of catalysts, membranes, and electrodes in practical electrolyzer conditions. The simultaneous optimization of these properties remains a central challenge, as materials that deliver excellent activity often suffer from limited stability, especially in the higher oxidative potential for the anode. Therefore, the development of robust, highly active materials is critical for advancing AEM electrolyzer technology toward practical, industrial deployment. Transition metals such as iron-triad (nickel, cobalt, and iron) are particularly promising due to their abundance, tunable physico-chemical properties, and excellent catalytic performance in alkaline environments. [1-2] Their adaptability also enables the design of advanced materials that are at the top to replace expensive noble metals, supporting the production of sustainable hydrogen. Herein, transition metal-based alloy and boride-derived materials are developed via scalable hydrothermal or chemical reduction, yet with comparable performance compared to PGM catalysts under similar alkaline conditions. As earth-abundant transition metal-based catalysts with exceptional bifunctionality for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are greatly desired, the enhanced OER performance of the MoNi catalyst simultaneously boosts HER activity.As a consequence, when assembled as a self-supported electrode in the AEMWE cell, a higher current density of 4.0 A cm -2 is achieved at a lesser than 2.0 V (without iR-compensation). Detailed physicochemical and electrochemical characterization indicates that both high-temperature chemical reduction and in situ structural reconstruction lead to the formation of a stable catalyst with platinum-group-metal-like properties for water electrolysis. Furthermore, through the controlled iterative reduction, a self-supported cobalt boride–phosphite electrode with mixed crystalline–amorphous phases is fabricated. [3] Microstructural and spectroscopic analyses confirm the one-pot method’s success in incorporating boron and phosphite to tune cobalt's microenvironment. This strategy enables precise catalyst design without thermal post-treatment, advancing phase engineering of metal boride nanomaterials. Acknowledgment This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 101102946. We acknowledge the funding from the project “DURALYS - DURAble, Scalable, and Recyclable Components and Cell Designs for Next Generation Alkaline Exchange Membrane Water Electrolysis” funded under the German-Italian Joint call for proposals on “Green Hydrogen Research: A Collaboration to Empower Tomorrow's Energy” within the framework of the collaboration between the German Federal Ministry of Education and Research (BMBF), the Italian Ministry of Foreign Affairs and International Cooperation (MAECI) and the Italian Ministry of University and Research (MUR). References 1. J. M. V. Nsanzimana, L. Cai, D. Abdoulaye, G. Pagot, P. Mattana, K. Vezzù, E. Negro, B. Y. Xia, V. Di Noto, Adv. Energy Mater. , 2025, 2501686. J. M. V. Nsanzimana, V. Jose, M. Sk, V. Reddu, L. Xiaogang, R. Dangol, R. Hao, Z. Huang, Q. Yan, R. Thapa, T. Maiyalagan, X. Wang, and J.-M. Lee, Small 2025, 21, 2500587 . 3. J. M. V. Nsanzimana, C. O. Ogolla, et al., J. Mater. Chem. A, 2025, 13 , 40655-40664 .

Anion exchange membranes (AEMs) are key components in emerging electrochemical technologies and are attracting increasing interest as alternatives to proton exchange membranes (PEMs). Polyketones have recently emerged as low-cost and easily tunable precursors for AEM fabrication; however, their conventional functionalization through the 1,4-diketonic moieties by convection heating requires prolonged reaction times (48-72 h), limiting process scalability and sustainability. Here, we report a microwave-assisted synthetic strategy to synthesize poly[ethylene pyrrole/ethylene ketone/propylene ketone] with morpholinium groups, achieving complete conversion within 3 h while preserving excellent yields (>95%), representing a significant improvement over the traditional thermal method. Moreover, precise control over the degree of functionalization is guaranteed. The resulting membranes (3MPA-FPKKf(X)(g), X = I, OH) were extensively characterized in the anionic form. They exhibited good thermal stability (up to 150 degrees C), and promising anion conductivity in the hydroxide form (4.5 mS cm(-1) at 80 degrees C). These properties underline the effectiveness of the proposed functionalization strategy and its potential to advance the development of polyketone based materials for ionic conduction applications.

Zinc-polyiodide flow batteries (FBs) offer a promising alternative to conventional vanadium-based systems, combining lower cost with the potential for higher energy density. In this work, we introduce an environmentally benign additive, consisting of a mixture of acetic acid and sodium acetate ligands, providing both buffering and metal complexing functions, to enhance reversibility and improve the morphology of zinc deposits at the anode. The additive operates via a dual mechanism: (i) modulating Zn2+-I- complexation to lower the energy barrier for zinc plating/stripping; and (ii) stabilizing the pH at the electrode-electrolyte interface to suppress side reactions leading to inactive byproducts. Single-cell tests demonstrate notable performance improvements over state-ofthe-art systems, with coulombic efficiency exceeding 98.2 % and energy efficiency reaching 85 % after 100 cycles. Spectroscopic and morphological analyses link these gains to the suppression of less active [ZnIx(H2O)4x]2- x species (for 2 <= x <= 4) and the inhibition of ZnO formation on the electrode surface during cycling. These findings highlight metal coordination by acetate ligand forming [ZnIxAcy(H2O)z]2-(x+y) species in solution as a simple, non-toxic, and effective strategy to improve the long-term performance of Zn-I2 FBs, paving the way for the development of more durable and energy-dense aqueous flow batteries.

The sluggish kinetics of the oxygen reduction reaction (ORR) hinder cost-effective polymer electrolyte fuel cells (PEFCs), which rely on scarce, expensive platinum-based electrocatalysts (ECs). Here, we present a novel synthesis method for ORR ECs achieving exceptional platinum utilization. The design features a hierarchical "multi-carbon" support comprising carbon nanoparticles interacting with graphene nanoplatelets as the "core", encapsulated by a porous carbon nitride (CN) "shell". This configuration promotes strong core/shell interactions and a bimodal active site distribution, consisting of chemically dispersed Pt and Ni single-atom complexes and PtNix alloy nanoclusters embedded in the CN shell. These advantages enable high activity and durability, achieving an ORR activity of 1.6 A mgPt-1 at 0.9 V vs. RHE-an order of magnitude higher than Pt/C (0.17 A mgPt-1). A proof-of-concept PEFC demonstrates a specific power of 12.0 kW gPt-1 at 0.60 V. This approach offers a significant step toward more efficient and sustainable PEFC technologies.

The development of efficient oxygen evolution reaction (OER) electrocatalysts free from platinum-group metals (PGMs) and cobalt is essential for advancing sustainable hydrogen production by alkaline water electrolysis. Multimetallic high-entropy oxide (HEO)-based systems offer unique opportunities to tune electrocatalytic performance through compositional complexity, phase engineering, and defect chemistry. In this study, a series of multiphasic HEO-based electrocatalysts containing Cr, Mn, Fe, Ni and Sn is synthesized, and the effects of calcination temperature (400 – 900 °C), calcination duration (2 – 9 h), and post-calcination cooling rate on their physicochemical properties and OER activity are systematically investigated. The synthesis conditions control the partitioning of Sn, Ni, and Fe among spinel HEO, rock-salt HEO, cassiterite, and NiFe carbonate/hydroxide phases, thereby affecting crystallinity, morphology, surface chemistry, defect-related features, and electrochemical performance. Several of the developed electrocatalysts outperform commercial IrOx in “ex-situ” OER measurements. Single-cell anion-exchange membrane water electrolysis tests further confirmed the superior performance of the best two electrocatalysts, which exhibited cell voltages 66 and 108 mV lower than that of the IrOx-benchmark cell at a current density of 1 A·cm-2. The corresponding cells also show practically unchanged polarization behavior during 24 h of operation, indicating short-term operational stability under the investigated AEMWE conditions. The enhanced activity is attributed to synthesis-controlled phase partitioning, minimized Sn segregation into cassiterite, the presence of reconstruction-prone HEO and NiFe carbonate/hydroxide (NiFe-CH) phases, and the small crystallite size of the reconstruction-prone components. Post-operation TEM/HRTEM and STEM-EDX analyses further reveal pronounced morphological and compositional reorganization of HEO-400/3 and HEO-500/2 after 24 h of AEMWE operation, consistent with the reconstruction of the electrocatalysts. These findings demonstrate the potential of Co- and PGM-free multiphasic HEO-based systems as high-performance OER electrocatalysts and provide design guidelines for advanced materials for alkaline water electrolysis.

This work presents a simple and efficient methodology for the synthesis of well‐defined fluorinated copolyphosphazenes incorporating 2,2,2‐trifluoroethan‐1‐olate (–OCH 2 CF 3 , TFE) and 3‐(diethylamino)phenolate (3DEAP) side groups, randomly distributed along the polymer chains, via living cationic polymerization. Two fluorinated copolyphosphazenes, 4a and 4b , with different CF 3 /3DEAP ratios (1:1 and 1:3, respectively), are prepared. The 3DEAP groups in these polymers are selectively and smoothly quaternized using methyl iodide (CH 3 I), yielding cationic fluorinated copolyphosphazenes 5a and 5b with quaternization degrees of ≈80% and 90%, respectively. These cationic copolymers, featuring tailored CF 3 /3DEMAP + ratios (3DEMAP + = 3‐(diethyl(methyl)ammonio)phenolate), exhibit complete water solubility and demonstrate self‐assembly in aqueous solutions, forming large compound micelles (LCMs) or bilayer vesicles depending on their composition. The amphiphilic nature of these materials, combining hydrophobic (CF 3 ) and hydrophilic (3DEMAP + ) moieties, enables their application in the efficient capture of anionic pollutants, such as sodium diclofenac (SDF) and perfluorooctanoic acid (PFOA), commonly found in wastewater. This study highlights the potential of these cationic fluorinated copolyphosphazenes as promising candidates for water decontamination and environmental remediation.

In this report, anion exchange membranes based on poly[(N-(1,4-dimethyl piperaziniumethyl)-ethylenepyrrole) (X)/ethyleneketone/propyleneketone/N-(n-butyl)ethylenepyrrole], where X = I- or OH-, terpolymer are prepared by converting the 1,4-diketonic groups of an aliphatic poly[ethylene ketone/propylene ketone] (PKK) into pyrrole substituted repeat units through a Paal-Knorr reaction. These materials are prepared by co-reacting 1-(2aminoethylpiperazine) and n-butylamine in different amines/PKK molar ratios to investigate the effect of varying degree of functionalization (f) and the incorporation of hydrophobic butyl pendant groups on the physicochemical properties of the membranes. The molecular structure and composition of the membranes are confirmed by ATR-FTIR and CHNS/O elemental analysis, while their electrochemical and physical properties are characterized through evaluation of water uptake (WU %), ion exchange capacity (IEC), thermal stability, ionic conductivity, and alkaline stability. BES studies reveal ionic conductivity values of 0.49 and 0.87 mS cm- 1 at 50 degrees C for the membranes in iodide and hydroxide form, respectively. The membrane PB-FPKK0.47/0.04(OH)0.43 demonstrates an exceptional chemical stability for 720 hours at 45 degrees C in 1 M KOH aqueous solution.

The electrochemical splitting of water for the production of “green hydrogen” holds great promise; however, the efficiency of the corresponding electrochemical reactions is crucial for its practical implementation. One of the main bottlenecks is the development of inexpensive and highly active electrocatalysts (ECs) for the oxygen evolution reaction (OER). Indeed, the latter process is typically slower than the hydrogen evolution reaction (HER), thus causing larger overpotentials. Spinel-structured transition metal (TM) oxides have emerged as promising and sustainable alternatives to ECs based on platinum-group metals (PGMs) for devices operating in an alkaline environment. Spinel-structured high-entropy oxides (SHEOs) with multiple TM-cation sites are ideal to design octahedral redox-active centers that can improve the EC activity [1,2]. The presence of surface oxygen vacancies contributes to achieve a promising electrochemical performance in the OER. In this work new (Cr, Mn, Fe, Sn, Ni) SHEOs are proposed, especially targeted to enhance the OER activity in the alkaline environment. The effect of calcination conditions on the electrochemical performance and surface-active sites of (Cr, Mn, Fe, Sn, Ni) SHEOs are investigated towards the alkaline OER. Changes in the chemical structure of SHEOs during single/multi-step calcinations at different temperatures are examined by XRD, ICP-AES, and NAP-XPS. The morphology is probed by SEM and TEM; the porosimetric features are assessed via nitrogen physisorption studies. The OER kinetics and mechanism are investigated by cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE). Particular attention is dedicated to elucidating the role of Sn in the modulation of: (i) the physicochemical features; and (ii) the electrochemical performance in the OER carried out in the alkaline environment. References [1] Vezzù, K., Triolo, C., Moulaee, K., Pagot, G., Ponti, A., Pinna, N., Neri, G., Santangelo, S. and Di Noto, V., Small, 2408319, 2024. [2] Triolo, C., Moulaee, K., Ponti, A., Pagot, G., Di Noto, V., Pinna, N., Neri, G. and Santangelo, S., Advanced Functional Materials, 34(6), 2306375, 2024. Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels” ]; and (b) the project DURALYS funded by the the Italian Ministry of Foreign Affairs and International Cooperation (MAECI).

Electrochemical energy storage and conversion systems hold immense potential to replace conventional fossil fuels as primary energy sources. Despite this, the widespread adoption of electrochemical energy technologies such as green hydrogen technology has been slow, as it has been hampered by several interconnected challenges. 1 Among the most important technical obstacles is the development of cost-effective and stable electrocatalysts (ECs). ECs play a crucial role in enhancing the efficiency of green electrochemical energy storage and conversion systems. Their use is essential for achieving sustainable energy solutions, as they enable the efficient conversion of clean energy sources into usable power while minimizing raw materials and energy losses. The state-of-the-art catalysts are based on scarce platinum-group metals (PGMs), which limit scalability. Consequently, the search for alternative materials is essential for enabling widespread adoption and advancing energy economy toward a zero-carbon-emission society. Earth-abundant transition metal-based ECs have received considerable interest as alternatives or co-catalysts to PGMs due to their favorable electronic properties and diverse redox activity. Key strategies to improve their performance include doping and alloying, where the introduction of non-metals or metalloids (e.g., nitrogen, phosphorus, sulfur, boron) or other metals modulates the electronic properties, improves conductivity, and enhances catalytic efficiency. In addition, hybrid materials of TM-based materials with heteroatom-doped carbon exhibit improved performance due to the high conductivity of carbon nanomaterials. For example, using this strategy, N-doped carbon–cobalt boride heterointerface catalysts have demonstrated superior performance in oxygen reduction reactions (ORR). 2 Although these advances have overall promoted TM-based catalysts as a potential candidate in electrochemical energy applications, the efficiency and durability still need to be further explored for practical use at large scale. For large-scale application of green energy technologies, the development of materials on a large scale is equally important. Therefore, cost-efficient approaches for material synthesis, such as one-pot synthesis, are desirable. However, this often limits the possibility of tailoring the catalytic activity, especially in the development of bifunctional electrocatalysts (ECs). From economic point of view, it is desirable to develop bifunctional ECs for chemical reactions that occur at the same electrode, such as the ORR and the oxygen evolution reaction (OER) in fuel cells and metal air batteries (MABs). For example, MABs could be simplified and made more cost-effective if a similar EC could function efficiently for both chemical reactions. The lack of bifunctional ECs for MABs such as zinc-air batteries (ZABs) is a significant bottleneck for this emerging battery technology. 3 This challenge arises because OER and ORR in ZABs follow different mechanisms, and require catalysts with different properties to efficiently perform these multistep reactions during charge and discharge cycles, while both processes occur on the same air electrode. Addressing these different requirements while maintaining long-term capability remains a critical hurdle to overcome and will lead to future discoveries of high-performance electrochemical energy systems. Based on these advances and the challenges of developing highly efficient and long-lasting bifunctional ECs, herein, we report the developed metal boride-derived nitrogen-doped carbon ECs for efficient hydrogen evolution reaction (HER) and oxygen electrolysis processes (OER and ORR). By comprehensive scale-bridge spectroscopic techniques, chemical elemental analysis, and electrochemical characterization, we established a structure-activity relationship. The advanced catalytic activity of these developed electrocatalysts is attributed to the presence of metal-nonmetal or metalloid interactions, together with a large surface area and a highly conductive heteroatom-doped graphitic carbon. This enabled the development of highly efficient and durable electrocatalysts through a combination of facile chemical reactions to form nanomaterials based on TMs as intermediates, which were further tailored through pyrolysis treatment to engineer hybrid system of transition-metal and carbon. In summary, simultaneous doping of heteroatoms in carbon and transition-metal nanoparticles is a promising approach for synthesizing highly efficient and stable ECs for OER and ORR and/or HER. The synthesis approach and the investigated structure-performance analysis provide valuable insights for the future discovery of multifunctional electrocatalysts based on PGMs-free materials for metal-air batteries, fuel cells, and water spliting. Acknowledgements This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement ID: 101102946. We acknowlege the support under the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels”]. References T. Terlouw, L. Rosa, et al., Nat. Commun. 2024 , 15 , 7043.. V. Jose, J. M. V. Nsanzimana, et al., Adv. Energy Mater. , 2021 , 11, 2100157. X. Zhang, Y. Liu, et al., Energy & Fuels , 2024 , 38, 19236-19252.

The slow kinetics of the oxygen reduction reaction (ORR) is one of the most relevant bottlenecks in the operation of proton exchange membrane fuel cells (PEMFCs). The latter technology is highly promising for a large-scale implementation, to promote the energy transition away from fossil fuels [1]. The best electrocatalysts (ECs) for the ORR in the acidic environment are based on platinum-group metals (PGMs), whose low abundance raises concerns associated to supply bottlenecks in the perspective of a large-scale rollout of PEMFC technology. Hence, the development of high-performing and durable ORR ECs able to minimize the PGM loading in the PEMFC cathode electrode is a major goal of the state of the art [2]. This work describes a new family of ORR ECs consisting of a carbonaceous support “core” covered by a carbon nitride (CN) “shell” , whose C- and N- “coordination nests” stabilize PtNi x nanostructures bearing the ORR active sites. The ECs are obtained by strongly coupling the carbonaceous support “core” with a binder-free macromolecular system wherein Pt and Ni atoms are bridged by cyano groups. The resulting precursor undergoes a multi-step pyrolysis process, during which: (i) the CN “shell” is formed on the “core” ; and (ii) PtNi x species (x ≈ 5) are nucleated on the CN “shell” . The final EC is obtained upon the application of a suitable electrochemical activation process, triggering the selective etching of excess Ni “co-catalyst” . It is studied the interplay between: (i) the synthetic features, focusing on the details of the pyrolysis process and the electrochemical activation; (ii) the physicochemical properties, especially in terms of chemical composition, morphology and structure; and (iii) the electrochemical performance. The latter is determined both: (i) “ex-situ” , by means of cyclic voltammetry with the rotating ring-disk electrode method (CV-TF-RRDE); this study is specifically aimed at evaluating the ORR kinetics and reaction mechanism; and (ii) “in-situ” , upon fabrication of membrane-electrode assemblies (MEAs) to be tested in operating conditions in single PEMFC. References [1] Hydrogen’s Big Shot, ECS Interface, 30(4), Winter 2021. [2] V. Di Noto et al. , ACS Catalysis, 12, 12291−12301 (2022). Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union - NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels” ]; and (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5.

Redox flow batteries (RFBs) represent a promising solution for large-scale energy storage, particularly in the context of integrating renewable energy sources into the power grid. Their unique architecture allows for independent scaling of power and energy, offering significant flexibility, long operational life, and enhanced safety compared to conventional battery systems. Despite these advantages, several challenges remain before RFBs can achieve widespread commercial deployment. Key issues include the relatively low energy density, high system costs, and the need for more sustainable and efficient electrolyte components. Overcoming these limitations is essential to improving their competitiveness and enabling broader adoption in energy storage applications. To address these challenges, research efforts are increasingly focusing on: a) the ionomer—the polymer material within the membrane and electrodes that governs ion transport and b) understanding the electrochemical processes at play. By tailoring the chemical structure and morphology of the ionomer, it is possible to enhance ion selectivity and conductivity, reduce crossover of active species, and improve overall cell performance and durability. Instead the understanding of the elettrochemical process shed light on a new scenario of phenomena that is necessary to master, in order to manage the operation of a RFB and to improve its long-term stability and charge retention ability, particularly under rest conditions. At the same time, exploring and designing new redox couples is critical for advancing RFB technology. The choice of redox-active species directly impacts the battery’s efficiency, stability, and environmental footprint. Developing more robust and earth-abundant redox couples can lead to higher energy densities, improved cyclability, and lower environmental impact, thus contributing to the creation of next-generation redox flow batteries.

The technology of Redox Flow Batteries is an important option to store energy from the operating irregularly renewable energy sources. The flow-based electrochemical energy storage systems utilize the appropriate electroactive species dissolved in externally flowing electrolytes which are ready to accumulate all (or part) of the charge. Among important issues is the search for highly efficient (i.e., capable of fast electron transfers) electroactive systems that would yield high power and energy densities during the systems’ operation. In the present work, we concentrate on utilization of highly concentrated iodine/iodide redox systems and their possibility to exhibit high rates of charge propagation. In practical terms, it can be combined with ZnI 2 , or other zinc salt, containing electrolyte. Reactions in the zinc/iodine (polyiodide) redox flow battery are as follows: Zn → Zn 2+ + 2e - (E = −0.76 V vs SHE) at the negative electrode (anode), and 3I - → I 3 − + 2e − (E = 0.54 V vs SHE) at the positive electrode (cathode) thus yielding a total theoretical potential output as high as ∼1.3 V. Obviously, the increase of current density can be achieved by reducing viscosity of the electrolyte. Alternatively - by analogy to the performance of iodine/iodide couple as charge relay in dye-sensitized solar cells – through improvement of the dynamics of charge propagation in highly concentrated iodine/iodide solution via the catalyzed enhancement of rates of electron self-exchange (hopping) between iodine/iodide (polyiodide) redox species as well as by accelerating the interfacial kinetics at electrodes. This can be realized by choosing appropriate electrode materials and through their activation or modification. The electrochemical activities of the redox couples are usually significantly increased through application of nanostructured functionalized carbons. While dispersed in solutions they can improve electron transfers to the redox sites. The proposed chemistry has been first tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation, heterogeneous and homogeneous (electron self-exchange) rates of electron transfers. Unless catalyzed, both interfacial and bulk (self-exchange) electron transfers involving the iodine/iodide redox system are somewhat complicated; there is a need to break the I-I bond in the I 3 - or I 2 molecule; it has also been well-established that platinum (e.g. when deposited on the counter electrode) induces electron transfers within the iodine/iodide redox system. In the presentation, we are going to explore the respective interfacial (electrocatalytic) phenomena on nanostructured metal oxides (e.g. zirconia), in addition to traces of expensive platinum or palladium nanoparticles (provided that catalytic centers are three-dimensionally distributed in the electrolyte phase), and we will utilize them to enhance iodine/iodide electron transfers to develop a new generation of redox mediators or ultra-fast components of redox electrolytes. Based on the results, it has been found that modification of the glassy carbon electrode with a layer of Nafion™ eliminates unwanted follow-up reactions (formation of polyiodides) in the iodine/iodide system, as well as the addition of iodine to the solution increases the reduction currents in each of the electrolytes tested. In addition, catalytic activity in the reduction reactions of the iodine/iodide system has also been demonstrated by cobalt(II,III) hexacyanoferrate(II) Finally, our results show that the catalyzed iodine/iodide system can reach extremely high electron self-exchange rates on the level of 10 9 – 10 10 mol -1 dm 3 s -1 .

The development of improved electrocatalysts (ECs) for the oxygen reduction reaction (ORR) is a critical stepping stone towards the large-scale rollout of proton-exchange membrane fuel cells (PEMFCs). Indeed, the ORR gives rise to large overpotentials (no less than ca. 300 mV), bottlenecking the overall energy conversion efficiency of the PEMFC. In addition, it is extremely challenging to obtain ORR ECs exhibiting a sufficient durability to comply with the requirements of applications. Our research group developed a synthetic route to obtain ORR ECs that is very different from those that are widely reported in the state of the art [1]. The proposed ECs consist of a “core-shell” support wherein a carbonaceous “core” is covered by a carbon nitride (CN) “shell” whose C- and N-functionalities form “coordination nests” stabilizing the metal active sites. The proposed synthetic route is extremely flexible and allows to tailor critical features of the ORR ECs, including the chemical composition and the morphology. This work reports a further refinement of the preparation route described above, with a systematic study focused to better elucidate the interplay between: (i) the synthetic parameters; (ii) the physicochemical properties; and (iii) the electrochemical performance of the resulting ECs. A full array of advanced analytical tools is adopted to comprehensively characterize the ECs. Specifically: (i) the bulk chemical composition is determined by inductively-coupled plasma optical emission spectroscopy (ICP-OES) and microanalysis; (ii) the porosimetric features are studied by nitrogen physisorption studies; (iii) the morphology is probed by electron microscopies, including ultra-high resolution scanning electron microscopy (UHR-SEM) and transmission electron microscopy (TEM); (iv) the surface chemical composition and the surface chemical state of the elements is investigated by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS); and (v) the structure is inspected by wide-angle X-ray diffraction (WAXD). “Ex-situ” electrochemical techniques yield information on: (i) the ORR active sites (by CO stripping); and (ii) the ORR performance and reaction mechanism (by cyclic voltammetry with the rotating ring-disk electrode, CV-TF-RRDE). The ECs are also used in the fabrication of single PEMFCs, whose performance is tested in a variety of operating conditions. Of particular relevance is the investigation of the impact of the partial pressure of oxygen at the cathode and the maximum power yielded by the PEMFC. The latter is prove crucial to clarify the role of the morphology and of the porosimetric features of the ECs towards the modulation of the losses due to mass transport, a major bottleneck for efficient PEMFC operation especially in the high-current regime that is relevant for practical applications. References [1] V. Di Noto et al. , ACS Catalysis, 12, 12291−12301 (2022). Acknowledgements This work has been supported under: (a) the National Recovery and Resilience Plan (NRRP), funded by the European Union – NextGenerationEU [Award Number: CNMS named MOST, Concession Decree No. 1033 of June 17, 2022, adopted by the Italian Ministry of University and Research, Spoke 14 “Hydrogen and New Fuels”, Flagship project 2023 – Line B – DHINAMIC and Flagship project 2024 – Line B – HERMES]; (b) the project PERMANENT financed in the framework of the Italian PNRR, M2C2, Investment Line 3.5; and (c) the project DURALYS funded under the German-Italian Joint Call for Proposals on “Green Hydrogen Research: A Collaboration to Empower Tomorrow’s Energy”.