Cation Modulation of Layered Self-Assembled Polyoxometalates Enables Efficient and Robust Hydrogen Evolution

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Polyoxometalate (POM) superstructures with tunable composition and diverse structures are gaining attention.
• The impact of alkyl chain length on POM superstructure architecture and performance, particularly for the hydrogen evolution reaction (HER), is not well understood.

Purpose of the Study:

• To investigate the influence of alkyl chain length in alkyl trimethyl ammonium bromide (TAB) surfactants on the self-assembly and electrochemical HER activity of POM superstructures.
• To establish a structure-performance relationship for designing advanced POM-based electrocatalysts.

Main Methods:

• Controlled self-assembly of four-layered superstructures using a giant POM (P8W48) and various alkyl TAB surfactants.
• Electrochemical characterization to evaluate HER activity, including overpotential measurements.
• In situ electrochemical spectroscopy and theoretical calculations to elucidate the mechanism.

Main Results:

• Alkyl chain length significantly affects POM superstructure architecture and HER performance.
• Short chains limit catalytic site accessibility, while long chains hinder charge transport.
• Superstructures assembled with cetyl TAB (P8W48-CTAB) demonstrated the highest HER activity, requiring only 55 mV overpotential for 10 mA cm-2.
• Enhanced interfacial electronic coupling and optimized active site density were observed in P8W48-CTAB.

Conclusions:

• A clear correlation exists between the organic cation alkyl chain length and the electrocatalytic performance of POM superstructures.
• Molecular-level self-assembly provides a pathway for designing multifunctional POM-based materials.
• Optimal alkyl chain length is crucial for maximizing HER efficiency by tuning electronic properties and active site accessibility.