Structurally disordered CoS_x-Co(OH)₂ heterointerface for boosting alkaline hydrogen evolution reaction

Area of Science:

• Electrochemistry
• Materials Science
• Nanotechnology

Background:

• Hydrogen evolution reaction (HER) is slower in alkaline than acidic media, necessitating advanced electrocatalysts.
• Structurally disordered heterostructure nanomaterials offer synergistic advantages of disordered and composite materials.
• Cobalt-based materials are cost-effective alternatives to precious metals for catalysis.

Purpose of the Study:

• To develop a high-performance, durable, and cost-effective electrocatalyst for alkaline HER.
• To investigate the synergistic effects of a disordered cobalt sulfide/hydroxide heterostructure (CoSx-Co(OH)2) on catalytic activity.
• To evaluate the practical feasibility of the developed catalyst in alkaline water electrolyzers.

Main Methods:

• In situ electrodeposition of CoSx-Co(OH)2 heterostructure onto a 3D microporous copper foam (CF) skeleton.
• Electrochemical characterization including half-cell HER tests and Tafel slope analysis.
• Durability testing over 1000 cycles and 500 hours of continuous operation.
• Fabrication and testing of a compact zero-gap alkaline electrolyzer.
• Density Functional Theory (DFT) calculations to elucidate reaction mechanisms.

Main Results:

• The CoSx-Co(OH)2/CF catalyst achieved a current density of 10 mA cm⁻² at an overpotential of 88 mV vs. RHE in 1 M KOH.
• The catalyst exhibited a favorable Tafel slope of 81.1 mV dec⁻¹, low charge-transfer resistance, and an enlarged electrochemically active surface area.
• Exceptional durability was demonstrated over 1000 cycles and 500 hours, with stable electrolyzer operation at 500 mA cm⁻² for ~240 hours.
• DFT calculations revealed a built-in electric field at the heterointerface facilitating electron transport and optimizing hydrogen adsorption/desorption.

Conclusions:

• The structurally disordered CoSx-Co(OH)2 heterostructure on CF provides a highly active and stable electrocatalyst for alkaline HER.
• The synergistic effects at the heterointerface, including enhanced water dissociation and H* conversion, significantly boost catalytic kinetics.
• The catalyst demonstrates practical feasibility for efficient and durable alkaline water electrolysis, offering a promising non-precious metal alternative.