Molecule-Based Proton-Electron Mixed Conductor with the Highest Ambipolar Conductivity.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Proton-electron mixed conductors (PEMCs) are crucial for hydrogen separation and energy conversion.
• Developing PEMCs with high ambipolar conductivity (σ_amb) is challenging due to difficulties in characterizing both proton and electron conduction mechanisms.

Purpose of the Study:

• To synthesize and characterize a novel molecule-based proton-electron mixed-conducting cation radical salt.
• To investigate the structural and conductive properties of the new material for potential applications.

Main Methods:

• Electrocrystallization was used to prepare the (ET)₄[Pt₂(pop)₂(Hpop)₂]·PhCN salt.
• Electronic conductivity was measured, and the metallic state was confirmed using magnetic susceptibility and band structure calculations.
• Proton conductivity was assessed, and structural studies (crystallography, computational) elucidated the hydrogen-bonding network responsible for proton transport.

Main Results:

• The synthesized salt exhibits metallic electronic conduction (σ_e = 1-2 S cm^-1) due to (ET)₂^•+ layers.
• Superprotonic conduction (σ_H = 2.1 × 10^-2 S cm^-1) was observed, facilitated by a 1D hydrogen-bonding network in the Pt-dimer complex anions.
• The material achieved the highest room temperature ambipolar conductivity (σ_amb = 2.1 × 10^-2 S cm^-1) among structurally defined PEMCs, comparable to metal oxides at high temperatures.

Conclusions:

• The molecule-based salt demonstrates excellent proton-electron mixed conduction properties.
• The findings highlight the potential of this material for practical applications in hydrogen separation and energy conversion devices.
• The study provides insights into the structure-property relationships governing mixed conduction in molecular materials.