Tailoring d-band centers in NiCo2O4 through phase engineering for high-performance ethanol oxidation and coupled hydrogen generation

Amorphous/crystalline heterostructures have emerged as an effective strategy for optimizing electrocatalytic performance by leveraging the complementary properties of both structural phases. In this study, a nickel cobalt spinel catalyst featuring an amorphous/crystalline heterophase (A/C-NiCo 2 O 4 /NF) was synthesized on nickel foam via a combination of hydrothermal treatment and electrochemical transformation. This heterostructured catalyst demonstrates significantly enhanced activity toward the ethanol oxidation reaction (EOR), achieving a high current density of 400 mA cm⁻ 2 at a low potential of 1.36 V. The nanoarray architecture, composed of interconnected hexagonal nanosheets, provides a high electrochemically active surface area, ensuring efficient exposure of catalytic sites. Electrochemical analyses reveal that the A/C-NiCo 2 O 4 /NF catalyst benefits from the synergistic integration of the high electrical conductivity inherent to the crystalline domains and the superior intrinsic catalytic activity of the amorphous regions. In contrast, its fully crystalline counterpart (C-NiCo 2 O 4 /NF) exhibits limited surface reconstruction and inferior EOR performance, underscoring the critical role of amorphization in facilitating catalytic enhancement. The unique amorphous/crystalline interface in A/C-NiCo 2 O 4 /NF facilitates electron redistribution, forming electron-deficient amorphous domains that promote OH¯ adsorption. Furthermore, a higher concentration of high-valence metal species in the catalyst enhances the in-situ generation of active CoO 2 intermediates. When integrated into a Pt-C/NF||A/C-NiCo 2 O 4 /NF ethanol-assisted electrolyzer, the system achieves a current density of 100 mA cm⁻ 2 at a cell voltage of just 1.7 V, enabling simultaneous hydrogen production and value-added acetate generation. • The A/C-NiCo 2 O 4 /NF catalyst exhibits significantly enhanced ethanol oxidation reaction (EOR) performance, achieving a high current density of 400 mA cm⁻ 2 at a low potential of 1.36 V, outperforming its fully crystalline counterpart (C-NiCo 2 O 4 /NF). • The heterostructured A/C-NiCo 2 O 4 /NF catalyst benefits from the combination of high electrical conductivity in crystalline domains and superior intrinsic catalytic activity in the amorphous regions, leading to improved electrocatalytic performance. • The amorphous/crystalline interface in A/C-NiCo 2 O 4 /NF facilitates electron redistribution, leading to electron-deficient amorphous domains that favor OH⁻ adsorption. This redistribution of electron density, along with modifications in the catalyst's d-band structure, enhances the adsorption of key reaction intermediates and optimizes catalytic activity. • The EOR-assisted electrolyzer delivers 100 mA cm⁻ 2 at 1.70 V with >95% Faradaic efficiency, enabling energy-efficient H 2 evolution and selective C 2 -product formation.