Room-Temperature Superprotonic Conductivity beyond 10^-1 S cm^-1 in a Co(II) Coordination Polymer

Area of Science:

• Materials Science
• Chemistry
• Energy Storage

Background:

• Efficient crystalline solid-state proton conductors (SSPCs) are vital for clean energy applications.
• Achieving high conductivity (≥10⁻¹ S cm⁻¹) at room temperature is a key challenge.

Purpose of the Study:

• To design and synthesize novel 1D Co(II) coordination polymers (CPs) as SSPCs.
• To investigate the effect of coordinated water and oxo-anions on proton conduction mechanisms.

Main Methods:

• Rational synthesis of two 1D Co(II) coordination polymers, PCM-2 and PCM-3.
• Characterization of their structures and proton conductivity under varying humidity and temperature.

Main Results:

• PCM-2 demonstrated ultrahigh superprotonic conductivity (1.03 × 10⁻¹ S cm⁻¹ at 25 °C, 95% RH), exceeding commercial Nafion 117.
• Enhanced proton conductivity in PCM-2 is attributed to cooperative H-bonding between metal-bound water and nitrate anions.
• PCM-3, lacking this H-bonding, showed significantly lower conductivity (5.87 × 10⁻⁵ S cm⁻¹ at 85 °C, 95% RH).

Conclusions:

• PCM-2 is the first SSPC to achieve 10⁻¹ S cm⁻¹ conductivity at ambient temperature with excellent recyclability.
• The coordinated-water-driven proton conduction mechanism, enhanced by specific H-bonding, is effective for designing high-performance SSPCs.