Toward Redox-Free Reverse Electrodialysis with Carbon-Based Slurry Electrodes

Area of Science:

• Electrochemistry
• Renewable Energy Technologies
• Materials Science

Background:

• Salinity gradient energy, specifically from reverse electrodialysis (RED), presents a clean and renewable energy source.
• The electrode system is critical for converting ionic to electrical current in RED.
• Conventional RED systems often rely on redox solutions, posing challenges to sustainability, stability, and economic viability.

Purpose of the Study:

• To investigate carbon-based slurry electrodes (CSEs) as a sustainable replacement for traditional redox solutions in RED.
• To evaluate the performance and characteristics of different CSE compositions for enhanced RED processes.
• To assess the long-term stability and economic potential of CSEs in RED applications.

Main Methods:

• A 0.10 × 0.10 m² RED stack with a cross-flow configuration was employed.
• Six distinct CSE compositions, utilizing activated carbon, carbon black, and graphite powder, were synthesized and tested.
• Key CSE characteristics measured included viscosity, pressure drop, maximum current density, stability, power density, and energy efficiency.

Main Results:

• Continuous operation of a single membrane configuration with CSEs for 17 days demonstrated stable electrical output.
• A CSE mixture of activated carbon and carbon black (20 wt %) achieved the highest net power density of 0.7 W·m⁻² using artificial seawater and river water.
• Higher current densities up to 350 A·m⁻² were explored, with feasibility demonstrated up to 150 A·m⁻² for electrodialysis (ED).

Conclusions:

• CSEs are a promising, versatile alternative to conventional electrodes in RED systems.
• The developed CSEs significantly enhance the sustainability, stability, and economic value of salinity gradient energy harvesting.
• Further research into CSEs can unlock broader applications in various electrochemical processes.