Operando spectroscopic analysis of an amorphous cobalt sulfide hydrogen evolution electrocatalyst

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Water electrolysis for H2 fuel generation is a key solar energy storage method.
• Efficient and affordable catalysts are crucial for large-scale hydrogen production.
• Amorphous hydrogen evolution reaction (HER) catalysts offer scalability but lack detailed structural understanding.

Purpose of the Study:

• To elucidate the structure and function of amorphous cobalt sulfide (CoSx) catalysts for HER.
• To understand the atomic-level mechanisms governing the catalytic activity of CoSx.

Main Methods:

• Raman spectroscopy was used to analyze the catalyst's structure.
• X-ray absorption spectroscopy (XAS) provided insights into the electronic and local structure.
• Operando experiments were conducted under catalytic conditions.

Main Results:

• Ex situ analysis showed as-deposited CoSx consists of small clusters with cobalt bonded to sulfur and oxygen.
• Operando XAS revealed an octahedral CoS2-like state under HER conditions.
• The active sites feature cobalt centers with a sulfur-rich first shell preferentially exposed to the electrolyte.

Conclusions:

• Amorphous CoSx catalysts form active CoS2-like clusters under cathodic polarization.
• These clusters present a high density of catalytically active sulfur sites for efficient HER.
• The findings provide a molecular model for understanding amorphous HER catalyst performance.