Sulfate-Terminated High-Entropy Oxyhydroxide Porous Nanocubes for Efficient Nitrate-to-Ammonia Conversion

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Coupling nitrate reduction (NO3RR) with oxygen evolution (OER) offers dual benefits but is hindered by slow reaction kinetics.
• Designing catalysts to overcome kinetic barriers for efficient ammonia synthesis and pollution mitigation is challenging.
• High-entropy materials (HEMs) show potential but require precise synthesis control.

Purpose of the Study:

• To develop a novel high-entropy catalyst for efficient bifunctional electrocatalysis.
• To investigate the electrochemical transformation and active species in the catalytic process.
• To elucidate the mechanisms behind enhanced performance in ammonia synthesis and OER.

Main Methods:

• Synthesis of porous high-entropy sulfide nanocubes (NiCoFeCuMn-S) as precatalysts.
• Electrochemical characterization including OER overpotential and NH3 Faradaic efficiency measurements.
• In situ spectroscopy and Density Functional Theory (DFT) calculations to study reaction mechanisms.

Main Results:

• Electrochemical transformation of NiCoFeCuMn-S into active sulfate-terminated oxyhydroxides (NiCoFeCuMnOOH-SO42-).
• Achieved ultralow OER overpotential (216 mV @ 10 mA cm-2) and high NH3 Faradaic efficiency (94.5%).
• Demonstrated high NH3 yield rate (21.8 mg h-1 mgcat-1) in alkaline electrolyte.
• DFT revealed coordinated sulfate lowers water dissociation barrier, enhancing NH3 synthesis.

Conclusions:

• Porous high-entropy sulfides are effective precatalysts for bifunctional electrocatalysis.
• The developed catalyst exhibits superior performance for simultaneous nitrate reduction and OER.
• This work presents a viable design strategy for efficient high-entropy electrocatalysts.
• The findings pave the way for sustainable ammonia synthesis and environmental remediation.