Ultrahigh-mobility microbial cytochrome nanowires generate power from humidity

Area of Science:

• Materials Science
• Biotechnology
• Energy Harvesting

Background:

• Mixed electronic-ionic conductors are vital for self-sustainable power generation technologies.
• Biological proteins have been explored as potential mixed conductors for decades.
• Previous research suggested Geobacter sulfurreducens pili filaments could generate power.

Purpose of the Study:

• To identify the specific biological components responsible for power generation in Geobacter sulfurreducens.
• To characterize the electronic and proton conductivity of these biological components.
• To elucidate the mechanisms behind humidity-enhanced conductivity and power generation.

Main Methods:

• Synthesis and characterization of cytochrome OmcZ nanowires from Geobacter sulfurreducens.
• Electrical conductivity measurements using AC impedance spectroscopy and four-probe van der Pauw methods.
• Field-effect transistor (FET) device fabrication and characterization.
• Electrochemical measurements to determine voltage and mobility requirements for power generation.

Main Results:

• Cytochrome OmcZ nanowires exhibit 20,000-fold higher electron conductivity compared to pili.
• Ultrahigh electron and proton mobility (>0.25 cm2/Vs) attributed to stacked hemes and charged surface.
• Humidity increases carrier mobility by 30,000-fold; cooling reduces activation energy.
• Generated potentials exceed 0.5 V, sufficient for sustained power output.
• High aspect ratio and hydrophilic surface facilitate efficient moisture capture and oxygen reduction.

Conclusions:

• Established cytochrome OmcZ nanowires as the primary power-generating component in Geobacter sulfurreducens.
• Demonstrated a new class of biologically-synthesized, low-cost, high-performance mixed conductors.
• Identified key design principles for enhancing power output through tunable electronic and protein structures.