Green hydrogen production from water electrolysis (WE) is one of the most promising technologies to realize a decarbonized future and efficiently utilize intermittent renewable energy. Among the various WE technologies, the emerging anion exchange membrane (AEMWE) technology shows the greatest potential for producing green hydrogen at a competitive price. To achieve this goal, simple methods for the large-scale synthesis of efficient and low-cost electrocatalysts are needed. This paper proposes a very simple and scalable process for the synthesis of nanostructured NiCo- and NiFe-based electrode materials for a zero-gap AEMWE full cell. For the preparation of the cell anode, oxides with different Ni molar fractions (0.50 or 0.85) are synthesized by the sol–gel method, followed by calcination in air at different temperatures (400 or 800 °C). To fabricate the cell cathode, the oxides are reduced in a H₂/Ar atmosphere. Electrochemical testing reveals that phase purity and average crystal size significantly influence cell performance. Highly pure and finely grained electrocatalysts yield higher current densities at lower overpotentials. The best performing membrane electrode assembly exhibits a current density of 1 A cm⁻² at 2.15 V during a steady-state 150 h long stability test with 1 M KOH recirculating through the cell, the lowest series resistance at any cell potential (1.8 or 2.0 V), and the highest current density at the cut-off voltage (2.2 V) both at the beginning (1 A cm⁻²) and end of tests (1.78 A cm⁻²). The presented results pave the way to obtain, via simple and scalable techniques, cost-effective catalysts for the production of green hydrogen aimed at a wider market penetration by AEMWE.

Green hydrogen production from water electrolysis (WE) is one of the most promising technologies to realize a decarbonized future and efficiently utilize intermittent renewable energy. Among the various WE technologies, the emerging anion exchange membrane (AEMWE) technology shows the greatest potential for producing green hydrogen at a competitive price. To achieve this goal, simple methods for the large-scale synthesis of efficient and low-cost electrocatalysts are needed. This paper deals with the synthesis of nanostructured NiCo- and NiFe-oxides and their evaluation as electrode materials in a zero-gap AEMWE full cell. Oxides with different Ni contents are synthesized by the sol-gel method, followed by calcination in air at different temperatures. The anode and cathode of the cell are fabricated using the as-prepared oxides and H2-/Ar-reduced oxides, respectively. Electrochemical testing of the synthesized catalysts reveals that phase purity and average crystal size significantly influence cell performance. Highly-pure and finely-grained electrocatalysts yield higher current densities at lower overpotentials. These findings underscore the critical role of catalyst composition and morphology in enhancing AEMWE efficiency, paving the way for scalable and cost-effective hydrogen production.

The development of sustainable and low-cost electrocatalysts based on Earth-abundant elements is essential for the large-scale deployment of green hydrogen production via anion exchange membrane water electrolysis (AEMWE). Herein, we demonstrate the feasibility of cobalt-free high-entropy oxide (HEO) electrodes for AEMWE through a set of spinel oxides based on equimolar Cr, Mn, Fe, Ni, and Zn. The HEOs were synthesized by a scalable sol-gel route followed by calcination at different temperatures (400–800 °C). The pristine oxides were employed as oxygen evolution reaction catalysts, whereas their H₂/Ar-reduced counterparts were used as hydrogen evolution reaction catalysts in symmetric membrane electrode assemblies (MEAs). Comprehensive physicochemical characterization combined with electrochemical testing revealed that the phase purity of the anodic catalyst mainly correlates with both the maximum current density and the polarization resistance of the electrolyzer. In contrast, a correlation is observed between the physicochemical features of the reduced cathodic catalyst, the iR-free potential and the polarization resistance after prolonged operation. The best-performing Co-free MEA achieved a current density of 0.51 A cm⁻² at 2.2 V and exhibited stable operation for hundreds of hours under alkaline electrolysis conditions. Although the complete replacement of cobalt results in lower activity than previously reported Co-containing HEOs, the present work establishes a viable design strategy for fully Co-free electrocatalysts and highlights the critical balance between catalytic performance, long-term stability, and material sustainability in future AEMWE technologies.

Spent lithium‐ion batteries represent a growing environmental challenge, yet their transition‐metal‐rich cathodes remain largely underutilized as functional materials. We report a direct upcycling strategy in which LiCoO ₂ cathodes recovered from end‐of‐life smartphones are transformed into efficient heterogeneous catalysts via a single‐step oxidative calcination (600 °C, 6 h, air). The resulting material retains a predominantly layered Li _{1− x} CoO ₂ structure with a minor spinel‐like phase formed during treatment. This reconstructed fraction significantly enhances cobalt reducibility, introducing a low‐temperature reduction feature absent in the untreated precursor. Under 20 bar H ₂ at 180 °C, the catalyst selectively converts furfural to furfuryl alcohol at short reaction times, while prolonged reaction promotes further hydrogenation to tetrahydrofurfuryl alcohol, enabling tunable selectivity. Compared with the untreated precursor and commercial references, the calcined material shows markedly improved catalytic activity. Computational simulations reveal that the spinel‐like phase provides the most favorable adsorption and activation of furfural, identifying it as the dominant catalytic motif. Catalyst deactivation is reversible, and activity is largely restored by a simple recalcination step. These results establish spent LiCoO ₂ cathodes as readily accessible cobalt‐based catalysts for upgrading biomass‐derived platform molecules, providing a circular route that couples battery‐waste valorization with sustainable chemical manufacturing.

Lattice defects, particularly oxygen vacancies, are commonly considered beneficial to photocatalytic performance, as they can reduce the bandgap, broaden the light absorption range, and suppress electron/hole recombination. In this perspective, high-entropy oxides (HEOs) could be considered “ideal” materials for photocatalysis because the random distribution of multiple metal cations within the crystalline lattice generates intrinsic structural disorder, which can be modulated by varying their composition and synthesis conditions. This work studies the photocatalytic activity of electrospun Cr–Mn–Fe–Co–Ni-based HEOs for the degradation of methylene blue in aqueous solution. The selected preparation conditions (calcination in air at 400 °C for 2 h) yield nanofibers consisting of ultra-small grains (≤9 nm) with copious oxygen vacancies on their surface. The presented results raise an important question: does the catalyst always promote the dye photodegradation or does it sometimes hinder it? A critical discussion is proposed, highlighting the case in which defects can induce competitive recombination pathways, negatively impacting the material’s photocatalytic performance.

In the perspective of replacing the use of fossil fuels with green and renewable alternatives, hydrogen can be considered a clean and sustainable energy carrier. There are multiple possible uses with a great number of applications and business sectors involved (power to gas, industry applications, residential uses, mobility etc.). One of the best cost effective and most environmentally friendly methods for the production of hydrogen is alkaline water electrolysis (AWE) powered by renewable resources [1]. In recent years, there has been a growing interest in high entropy materials (HEMs), including high entropy alloys (HEAs), high entropy oxides (HEOs), and other similar compounds. These materials are characterized by their unique structure, which combines antisite disorder with crystalline periodicity [2]. Although initially studied mainly for structural applications, their extraordinary properties are opening up new possibilities in energy fields, such as catalysis [3,4]. The project “HEM4GREEN” (High-Entropy Materials as cost-effective catalysts in anion exchange membrane water electrolysis for GREen hydrogEN production) has as main purpose the development and engineering of novel nanostructured CRM-free electrocatalysts based on HEM, to be used in an electrolyzer employing a polymeric anion exchange membrane (AEM) as the electrolyte. Low-entropy CoNi and NiFe based oxides for the anode and CoNi and NiFe based alloys for the cathode have been synthesized and characterized by means of different techniques (XRD, MRS, SEM). Electrodes were fabricated by ink spraying and assembled in a zero-gap AWE full cell, which were electrochemically tested. HEMs were also prepared by scalable techniques, suitable for mass-production and characterized in terms of physio- and electrochemical properties. Electrochemical testing indicates that samples preparation conditions strongly influence cell performance. The Authors gratefully acknowledge the European Union for the financial support to this project through Next-Generation EU funds (National Recovery and Resilience Plan, PNRR - Mission 4 “Education and Research” - C2 component - Investment 1.1, Fund for the National Research Program and Projects of Relevant National Interest, PRIN). [1] S. Campagna Zignani, M. Lo Faro, A. Carbone, C. Italiano, S. Trocino, G. Monforte, A.S. Aricò, Electrochim. Acta 2022, 413, 140078. [2] S. Schweidler, M. Botros, F. Strauss, Q. Wang, Y. Ma, L. Velasco, G.C. Marques, ... B. Breitung, Nature Rev. Mater. 2024,9, 266. [3] K. Huang, J. Xia, Y. Lu, B. Zhang, W. Shi, X. Cao, X. Zhang, L.M. Woods, C. Han, ... Y. Huang, Adv. Sci. 2023, 10, 2300094 [4] C. Triolo, K. Moulaee, A. Ponti, G. Pagot, V. Di Noto, N. Pinna, G. Neri, S. Santangelo Adva. Funct. Mater. 2024, 34, 2306375.