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.