Temperature-Dependent Protonic Exchange Affects Blue Energy Generation in Soft Nanochannels

Area of Science:

• Nanofluidics
• Renewable Energy Harvesting
• Electrochemistry

Background:

• Blue energy harvesting utilizes salinity gradients for power generation.
• Ion selectivity and electrochemical coupling are crucial at the nanoscale.
• Polyelectrolyte layers (PELs) in nanochannels influence ion transport.

Purpose of the Study:

• To numerically investigate electrical energy generation in a PEL-grafted nanochannel under coupled salinity and temperature gradients.
• To model temperature-dependent PEL ionization, ion partitioning, electrothermal-ionic transport, and thermo-diffusion.
• To analyze the impact of these factors on ion selectivity and power output.

Main Methods:

• Developed a comprehensive numerical framework using Poisson-Nernst-Planck (PNP) and energy equations.
• Employed a finite-element approach for solving the model.
• Validated the numerical model against theoretical, experimental, and steady-state PNP solutions.

Main Results:

• Temperature-dependent PEL ionization critically regulates space charge density and local pH.
• Increasing reservoir temperature reduces PEL ionization strength and shifts neutral pH to more acidic conditions.
• Ion partitioning creates a basic PEL region and acidic core, enhancing cation selectivity (>0.5 transference numbers).
• Increased pH and temperature significantly boost ionic current, maximum pore power, and power density.
• Achieved power density exceeding 5 W m^-2 and energy conversion efficiency over 30% at alkaline pH.

Conclusions:

• PEL-modified nanochannels offer efficient blue energy harvesting potential.
• Coupled thermal and chemical gradients significantly enhance energy conversion efficiency.
• The developed numerical framework provides a valuable tool for designing advanced nanofluidic energy harvesters.