Tuning Defects in Ni-Doped Maghemite for Enhanced Solar Driven Oxygen Evolution: Insights From Operando X-Ray...

Area of Science:

• Materials Science
• Catalysis
• Electrochemistry

Background:

• Maghemite ($\gamma$ - ${\mathrm{Fe}}_2$ $O_3$) is a promising non-precious metal photocatalyst for water oxidation.
• It offers corrosion resistance, a favorable band structure, high conductivity, and an adaptable spinel structure, outperforming Hematite in some aspects.
• Catalytic performance can be improved by doping with donor elements.

Purpose of the Study:

• To synthesize and characterize ultra-thin Ni-doped maghemite films.
• To investigate the effects of varying Ni concentrations on structural and electronic properties.
• To evaluate the impact of Ni doping on oxygen evolution reaction (OER) onset and photoconversion efficiency.

Main Methods:

• Synthesis of 6 nm Ni-doped $\gamma$ - ${\mathrm{Fe}}_2$ $O_3$ (111) films using molecular beam epitaxy.
• X-ray Absorption Spectroscopy (XAS) to study electronic reconfiguration and the role of Ni.
• X-ray fluorescence (XRF) pump-and-probe spectroscopy, specifically Fixed energy X-ray absorption PhotoVoltammetry, to probe light-driven surface chemistry modifications.

Main Results:

• Successful synthesis of ultra-thin Ni-doped maghemite films with controlled Ni concentrations.
• Demonstrated correlation between Ni concentration, structural reconfigurations, and enhanced OER performance.
• Identified the electronic reconfiguration and catalytic mechanism influenced by Ni doping under operando conditions.

Conclusions:

• Ni doping is an effective strategy to tune the catalytic properties of maghemite for water oxidation.
• Optimized Ni concentrations lead to improved OER onset potential and photoconversion efficiency in alkaline media.
• The study provides insights into the fundamental mechanisms of Ni-doped maghemite photocatalysis for energy conversion applications.