Plasma-assisted fabrication of NiO nanoarchitectures: from design to oxygen evolution electrocatalysis

Abstract

Electrocatalytic oxygen evolution reaction (OER), playing a key role in water splitting processes to yield green hydrogen, is critically dependent on the implementation of stable, efficient, and economically viable catalysts. Among the various runners, NiO-based nanomaterials have recently gained considerable attention. Herein, we focus on the plasma enhanced-chemical vapor deposition (PE-CVD) of NiO nanoarchitectures, grown on conducting glasses from a fluorinated Ni(II) precursor and subjected to a comprehensive experimental and theoretical characterization. Modulations of the growth temperature from 100 to 400 °C yielded a progressive evolution from hierarchical quasi-1D nanopillars, featuring the surface presence of CF_x groups, to cauliflower-like structures, characterized by a homogeneous fluorine distribution inside NiO. The open morphology of the 100 °C-grown system, possessing a higher content of structural defects, enhanced charge carrier transport and promoted reactants/products diffusion, yielding the best activity among the investigated materials (overpotential of ≈390 mV at 10 mA × cm⁻² and Tafel slope of 39 mV × dec⁻¹). Density functional theory (DFT) modeling indicates that CF_x groups create intra-gap empty states which could promote OER activity. The obtained performances compare favorably with various Ni-based electrocatalysts reported up to date, opening the door to additional research developments towards sustainable energy generation.