Microscopic view of thermoelectric element after wet etching.

Thermoelectric Breakthrough: Enhancing Efficiency with Innovative Wet Etching

Jordan Keane in Tech & Innovation August 2025 • 5 min read.

"New Research Reveals How Wet Etching Can Significantly Improve the Performance of Thermoelectric Devices"

Thermoelectric modules are gaining increased attention as a promising avenue for sustainable energy solutions, capable of converting heat energy directly into electricity and vice versa. These modules leverage the Seebeck effect, generating electric currents from temperature gradients, and the Peltier effect, creating temperature differences through electric currents. Their application in thermoelectric generators requires numerous elements to be connected in series, making the quality and reliability of each bond critical to overall performance.

A significant challenge in the fabrication of these modules lies in ensuring robust and durable connections between the thermoelectric elements and the conductive layers. Traditional soldering methods often suffer from the formation of brittle intermetallic compounds, particularly when using tin-based solders with telluride-based thermoelectric materials. These compounds degrade the bond strength over time, reducing the module's efficiency and lifespan. A common solution involves creating a diffusion barrier, often a nickel or nickel alloy layer, between the thermoelectric material and the solder.

Electroless plating is an attractive method for applying these barrier layers, offering uniform coating thickness even on complex shapes. However, achieving strong adhesion between the electrolessly plated layer and the thermoelectric element can be difficult. Surface treatments like sandblasting have been used to enhance adhesion by increasing surface roughness, but this method can introduce unwanted physical damage. Recent research explores a gentler approach: wet etching. Wet etching uses chemical solutions to selectively remove material from the surface, creating a controlled roughness without the drawbacks of mechanical methods.

The Science Behind Wet Etching for Enhanced Thermoelectric Performance

Microscopic view of thermoelectric element after wet etching.

A study published in the Journal of Nanoscience and Nanotechnology details a novel wet etching method to improve the electroless nickel-phosphorus (Ni-P) plating on bismuth-telluride (Bi-Te) thermoelectric elements. The research focuses on creating a reliable and efficient fabrication process for thermoelectric modules, addressing common issues related to bond strength and durability. The team, led by Sung Hwa Bae from Kyungpook National University, investigated the impact of wet etching on the surface properties of Bi-Te elements and the resulting adhesion of the Ni-P plating.

The experimental procedure involved several key steps: sintering commercial n-type (Bi2Te2.7Se0.3) and p-type (Bi0.5Sb1.5Te3) Bi-Te ingots using spark plasma sintering (SPS). These sintered pellets were then cut into thin disks, followed by a wet etching process using a nitrate solution. After etching, the samples underwent a cleaning process to remove any residual chemicals before being immersed in a palladium catalyst solution. This step is crucial for initiating the electroless Ni-P plating, which was carried out in a commercial solution at 90°C for 20 minutes, resulting in a uniform Ni-P layer approximately 3 micrometers thick.

Improved Adhesion: Wet etching significantly increased the surface roughness of the Bi-Te thermoelectric element, creating an anchoring effect that enhanced the adhesion of the Ni-P plating.
Enhanced Bond Strength: Thermoelectric modules fabricated using the wet etching method demonstrated excellent bond strength, with values around 10 MPa.
Heat Treatment Stability: The Ni-P plating exhibited remarkable adherence, even after heat treatment at 200°C for 24 hours, indicating its suitability for high-temperature applications.
Uniform Plating: The electroless plating method ensured a uniform thickness of the Ni-P layer, crucial for consistent performance of the thermoelectric module.

The results of the study indicated that wet etching effectively roughens the surface of the Bi-Te thermoelectric elements, providing an increased surface area for the Ni-P plating to adhere. Confocal laser scanning microscopy and scanning electron microscopy (SEM) images confirmed the enhanced surface roughness after etching. Shear strength tests demonstrated that modules fabricated with the wet etching method exhibited robust bond strength, comparable to modules treated with sandblasting. Furthermore, the Ni-P plating remained intact and adhered well to the Bi-Te elements, even after being subjected to high-temperature heat treatment, a critical requirement for many thermoelectric applications. Further analysis using energy-dispersive X-ray spectroscopy (EDS) confirmed the presence and distribution of key elements at the bonding interface, highlighting the effectiveness of the wet etching process in creating a strong and reliable connection.

Future Directions and Implications

This research demonstrates the potential of wet etching as a viable and effective method for enhancing the fabrication of thermoelectric modules. By carefully controlling the etching process, it is possible to create a surface roughness that promotes strong adhesion of electrolessly plated layers without causing physical damage to the thermoelectric material. This approach can lead to more durable and efficient thermoelectric devices, which are essential for various applications, including waste heat recovery, automotive thermoelectric generators, and portable power sources. Future studies could focus on optimizing the etchant composition and etching parameters to further improve the performance and reliability of thermoelectric modules.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1166/jnn.2019.16247, Alternate LINK

Title: Wet Etching Method For Electroless Ni–P Plating Of Bi–Te Thermoelectric Element

Subject: Condensed Matter Physics

Journal: Journal of Nanoscience and Nanotechnology

Publisher: American Scientific Publishers

Authors: Sung Hwa Bae, Hyo Jae Jo, Injoon Son, Ho-Sang Sohn, Kyung Tae Kim

Published: 2019-03-01

Everything You Need To Know

What are thermoelectric modules and how do they utilize the Seebeck and Peltier effects for sustainable energy?

Thermoelectric modules utilize the Seebeck effect, which generates electric currents from temperature gradients, and the Peltier effect, which creates temperature differences through electric currents. These effects are crucial for converting heat energy directly into electricity and vice versa, making thermoelectric modules a sustainable energy solution. The efficiency of these modules depends heavily on the connections between thermoelectric elements and conductive layers. The wet etching process helps to create more robust and durable connections.

How does wet etching improve the adhesion of electroless nickel-phosphorus (Ni-P) plating on bismuth-telluride (Bi-Te) thermoelectric elements, and why is this significant?

Wet etching improves the adhesion of the electroless nickel-phosphorus (Ni-P) plating on bismuth-telluride (Bi-Te) thermoelectric elements by creating a controlled roughness on the surface. This increased surface roughness provides an anchoring effect, enhancing the bond strength between the Ni-P plating and the Bi-Te material. Unlike sandblasting, wet etching achieves this without causing physical damage to the thermoelectric material, making it a gentler and more effective method.

What is the role of electroless nickel-phosphorus (Ni-P) plating in the fabrication of thermoelectric modules after wet etching, and how does it contribute to module performance?

The electroless nickel-phosphorus (Ni-P) plating is applied to bismuth-telluride (Bi-Te) thermoelectric elements after wet etching. The wet etching roughens the surface of the Bi-Te, and the electroless plating ensures a uniform coating of Ni-P. This method provides consistent performance of the thermoelectric module. The Ni-P plating acts as a diffusion barrier, preventing the formation of brittle intermetallic compounds that can degrade the bond strength over time.

Can you describe the experimental procedure used in the study to enhance thermoelectric performance through wet etching and electroless plating?

The study, published in the *Journal of Nanoscience and Nanotechnology*, involved sintering commercial n-type (Bi2Te2.7Se0.3) and p-type (Bi0.5Sb1.5Te3) Bi-Te ingots using spark plasma sintering (SPS). These ingots were then cut into thin disks and underwent a wet etching process using a nitrate solution. After cleaning, the samples were immersed in a palladium catalyst solution to initiate the electroless Ni-P plating, which was performed in a commercial solution at 90°C for 20 minutes. This resulted in a uniform Ni-P layer approximately 3 micrometers thick. The research was led by Sung Hwa Bae from Kyungpook National University.

How does the enhanced adhesion and bond strength achieved through wet etching and electroless plating impact the durability and application of thermoelectric modules in high-temperature environments?

The enhanced adhesion and bond strength achieved through wet etching and electroless nickel-phosphorus (Ni-P) plating contribute to the durability and longevity of thermoelectric modules. The Ni-P plating's ability to withstand heat treatment at 200°C for 24 hours, without losing adherence, makes these modules suitable for high-temperature applications. This durability is critical for applications such as waste heat recovery and automotive thermoelectric generators, where the modules are exposed to harsh conditions.