Abstract
CoSb3-based skutterudite alloy is one of the most promising thermoelectric materials in the middle temperature range (room temperature—550 °C). However, the realization of an appropriate metallization layer directly on the sintered skutterudite pellet is indispensable for the real thermoelectric generation application. Here, we report an approach to prepare the metallization layer and the subsequent diffusion bonding method for the high-performance multi-filled n-type skutterudite alloys. Using the electroplating followed by low-temperature annealing approaches, we successfully fabricated a Co-Mo metallization layer on the surface of the skutterudite alloy. The coefficient of thermal expansion of the electroplated layer was optimized by changing its chemical composition, which can be controlled by the electroplating temperature, current and the concentration of the Mo ions in the solution. We then joined the metallized skutterudite leg to the Cu-Mo electrode using a diffusion bonding method performed at 600 °C and 1 MPa for 10 min. The Co-Mo/skutterudite interfaces exhibit extremely low specific contact resistivity of 1.41 μΩ cm2. The metallization layer inhibited the elemental inter-diffusion to less than 11 µm after annealing at 550 °C for 60 h, indicating a good thermal stability. The current results pave the way for the large-scale fabrication of CoSb3-based thermoelectric modules.
Highlights
Thermoelectric materials have attracted great attention for centuries because they can directly convert heat to electricity, and vice versa [1]
Since the skutterudite-based thermoelectric generators usually work between 50 ◦ C and 600 ◦ C, it is necessary to prepare a barrier layer on the surface of the skutterudite
The choice of the barrier layer needs to meet the following criteria: (i) The barrier layer can simultaneously form a finite reaction layer with the skutterudite compound and the electrode to form a high-strength joint. (ii) The barrier layer should possess a similar coefficient of thermal expansion (CTE) to that of the skutterudite compound and the metal electrode. (iii) The interfacial electrical and thermal resistances caused by the introduction of the barrier layer should be as low as possible
Summary
Thermoelectric materials have attracted great attention for centuries because they can directly convert heat to electricity, and vice versa [1]. The skutterudite (SKU) compound is one of the most promising thermoelectric materials for the middle temperature range of thermoelectric generation. In the fabrication of a thermoelectric device, both p-type and n-type thermoelectric materials are required to be connected with the metal electrodes [9]. Copper and nickel are the common electrode materials for the thermoelectric devices. When the electrode connects to the skutterudite compounds directly, they react violently. This reaction results in a great degradation
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