3D-Printed Ion-Conductive Spacers for Enhanced Reverse Electrodialysis in Salinity Gradient Energy Systems

Abstract

Reverse electrodialysis is a membrane-based technology that utilizes the salinity gradient between two solutions (e.g. river water and seawater) to generate sustainable energy. A critical component of RED systems is the spacer, which ensures effective flow distribution and ion exchange through the membranes. Conventional spacers suffer from the shadow effect, which limits ion transport and reduces power output. Moreover, the low ion conductivity in the solution with lower salt concentration leads to higher resistance, influencing power density. This
project explores the modeling, functionalization and electrochemical performance of 3D-printed ion-conductive spacers to overcome these limitations.

Spacers with different open areas were fabricated using fused deposition modeling, a 3D-printing technique. Ion-conductive spacers were prepared by sulfonation of 3D-printed spacers. Characterization techniques including ion exchange capacity, energy-dispersive X-ray spectroscopy and swelling measurement were employed to understand the degree of sulfonation. An optimal sulfonation time of 15 minutes resulted in a sulfonation degree of 1.22 meq/g while maintaining mechanical stability. Electrochemical testing was conducted on 2 cell and 5 cell
RED stacks using artificial feed solutions. The effects of varying river water concentration (concentration gradient), and spacer type on RED performance parameters were analyzed. Increasing the open area of 3D-printed spacer from 58 to 85% improved the power density by 38%. The best performing condition, using seawater (0.5 M) and river water (0.0051 M) with sulfonated spacer, achieved a maximum power density of 0.78 W/m2, 2.7-fold higher than that of commercial spacers. Using 5-cell, it was possible to achieve the same enhancement factor,
with only slight variation in power density. Additionally, functionalized spacers contributed to 27% improvement in power density compared to the non-functionalized spacers with identical geometry. Further testing with synthetic saline solution with multivalent ions, simulating natural waters condition, showed a 17% reduction in power density due to increased membrane resistance and lowered open-circuit voltage. These results indicate that a custom-made 3D-printed ion-conductive spacer tailored for RED application could enhance the system performance. Future research should investigate the performance of these spacers with natural waters and evaluate their long-term stability under continuous operations.

Popular Abstract

“Where the river greets the sea, nature whispers the possibility of clean energy”

The world’s energy demand is continuously growing, and relying on fossil fuels is causing sever environmental impact. As a result, shifting towards renewable energy sources has become crucial. While solar panels and wind turbines are well-established renewable energy sources, they heavily depend on weather conditions such as sunlight and wind, leading to fluctuations in power output. In comparison, hydropower is more reliable, but constructing large dams can disrupt natural water flows and impact ecosystems.

But what if continuous clean energy could be harnessed from the natural mixing of river water and seawater without disrupting the natural water cycle?

Every day, rivers carry massive amounts of freshwater into oceans and seas as part of the Earth’s natural water cycle. When freshwater meets seawater, energy is released as the salt ions spread from the salty seawater to the river water, a fundamental process driven by nature’s desire for balance. This energy source is known as salinity gradient power or “Blue Energy”. Globally, it is estimated that salinity gradient power could provide over 1 terawatt of clean energy. To put
this into perspective, 1 terawatt is equivalent to the combined output of 1000 nuclear power plants. More importantly, this energy can be harnessed without producing any emissions or waste and without building dams that change landscapes and ecosystems.

Reverse electrodialysis is one of the technologies that can access this energy. This technology uses thin, special membranes that act as smart filters. During the mixing process of seawater and fresh water inside this device the salt ions want to move from the salty water to the fresh water. However, these special membranes stacked together sort the salt ions based on their charge: positively charged ions move in one direction and the negatively charged ions move to the other side. This separation of positive and negative charge creates a voltage, just like a battery, which is directly converted to usable electricity.

To prevent the membranes from sticking together and to allow water flow, thin supports called spacers are placed between them. However, spacers have a limitation, they act like roadblocks. They partially block the path of salt ions trying to pass through the membranes, preventing them from reaching where they need to go and reducing the system efficiency and power output.

This study focused on enhancing the reverse electrodialysis performance by improving spacer design. 3D-printing was employed to fabricate custom designed spacers with higher open area and conductive property that facilitate charged particles transport through the membranes. When tested with synthetic river water and seawater, these spacers boosted the power generation by 2.7-times compared to conventional spacers. These results show that 3D-printed conductive spacers can enhance reverse electrodialysis efficiency and power generation. Future
work should focus on testing these spacers under real-world conditions using natural waters.

• author: Halefom, Alula Gebregergs
• supervisor: Frank Lipnizki; Ahmet Halil Avci
• organization: Chemical Engineering (M.Sc.Eng.)
• course: METM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Blue Energy, Salinity Gradient Power, Reverse Electrodialysis, 3D-Printing, Fused Deposition Modeling, Ion-conductive Spacer, Seawater, River Water, Membrane Engineering, Membrane Technology
• language: English
• id: 9203685
• date added to LUP: 2025-06-23 11:33:55
• date last changed: 2025-06-23 11:33:55