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Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Efficient hydrogen production via electrochemical water splitting requires earth-abundant, high-performance bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes.
• Developing such catalysts remains a significant challenge in sustainable energy technologies.

Purpose of the Study:

• To fabricate and evaluate mesoporous cobalt iron oxide inverse opals (m-CFO IO) as bifunctional electrocatalysts for OER and HER.
• To investigate the effect of cobalt and iron ratios on catalytic performance.

Main Methods:

• Fabrication of m-CFO IO using a wet chemical method with polystyrene beads as a hard template, followed by calcination.
• Electrochemical characterization of OER and HER performance using techniques like overpotential and Tafel slope measurements.
• Testing in an alkaline water electrolyzer with a two-electrode configuration.

Main Results:

• The m-CFO IO catalyst with equal Fe and Co concentrations demonstrated excellent OER and HER performance.
• Achieved low overpotentials (261 mV for OER, 157 mV for HER) and small Tafel slopes (63 mV dec-1 for OER, 56 mV dec-1 for HER).
• An alkaline water electrolyzer using this catalyst reached 10 mA cm-2 at 1.55 V with superior long-term stability compared to IrO2 and Pt/C benchmarks.

Conclusions:

• The m-CFO IO catalyst exhibits remarkable bifunctional activity for OER and HER.
• The enhanced performance is attributed to synergistic effects including optimal particle size, crystallinity, oxygen content, numerous active sites, and a high surface area from the porous inverse opal structure.
• This catalyst represents a promising alternative to noble metal catalysts for efficient electrochemical water splitting.