The Shanghai Institute of Ceramics has made significant progress in the research on flexible organic/inorganic thermoelectric composites.

Shenjia Hydraulics

Release time:

2020-05-26

The Shanghai Institute of Ceramics has made significant progress in the research on flexible organic/inorganic thermoelectric composites.

Flexible thermoelectric energy conversion technology can convert temperature differences in the environment or on the human body into electrical energy, enabling self-powered electronic devices and holding great promise for applications in fields such as wearable electronics. Traditional inorganic thermoelectric materials exhibit excellent thermoelectric performance but lack flexibility; while organic thermoelectric materials, though highly flexible and bendable, suffer from extremely low thermoelectric efficiency. Organic/inorganic composite thermoelectric materials, which combine the high thermoelectric performance of inorganic materials with the superior flexibility and bendability of organic materials, have become a research hotspot in recent years. One-dimensional carbon nanotubes or metal nanowires, with their unique one-dimensional structure, can form tightly connected conductive networks with one-dimensional molecular chains in organic materials, providing high-conductivity pathways along these chain networks. Consequently, they are often employed in the study of organic/inorganic composite thermoelectric materials. However, the extremely low Seebeck coefficient of carbon nanotubes or metal nanowires makes it difficult to enhance the Seebeck coefficient of the resulting composites. Although inorganic thermoelectric materials boast high Seebeck coefficients, their shapes are typically flaky or granular, leading to poor electrical transport properties in the composites. Therefore, selecting matching organic and inorganic materials to achieve optimal electrical transport has become a key scientific challenge in the research on organic/inorganic composite thermoelectric materials.

Recently, Researcher Shi Xun, Researcher Chen Lidong, Associate Researcher Qiu Pengfei, and Associate Researcher Qu Sanyin from the Shanghai Institute of Ceramics, Chinese Academy of Sciences, in collaboration with Professor Jian He from Clemson University in the United States, proposed a new strategy for designing thermoelectric composites based on dimensional matching. Specifically, they used inorganic semiconductor materials with one-dimensional structures to fabricate high-performance PVDF/Ta4SiTe4 organic/inorganic flexible thermoelectric composite films. The prototype device achieved the highest normalized maximum power density reported so far among flexible thermoelectric devices, under a temperature difference of 35.5 K. The related research findings, titled “Conformal organic–inorganic semiconductor composites for flexible thermoelectrics,” were published in Energy & Environmental Science.

The organic material polyvinylidene fluoride (PVDF) features a one-dimensional chain-like structure and is an excellent flexible insulator. Based on the design concept of dimensional matching, the team selected Ta4SiTe4—a inorganic material also with a one-dimensional structure—and combined it with PVDF to fabricate organic/inorganic flexible composite films. Through chemical vapor transport reactions, they obtained one-dimensional Ta4SiTe4 whiskers doped with 0.5% Mo at the Ta sites. Subsequently, using N,N-dimethylformamide (DMF) as a dispersant, they prepared PVDF/Ta4SiTe4 composite films via the spin-coating method. Scanning electron microscopy revealed that the Ta4SiTe4 whiskers were uniformly dispersed within the PVDF matrix, forming a network-like structure. Transmission electron microscopy showed that the Ta4SiTe4 whiskers formed a tightly bonded two-phase interface with the PVDF. Thermoelectric characterization demonstrated that the PVDF/50 wt% Ta4SiTe4 composite exhibited outstanding electrical transport properties, with a power factor reaching as high as 1060 μWm⁻¹K⁻² at 220 K. In particular, at the same electrical conductivity, the Seebeck coefficient of the PVDF/50 wt% Ta4SiTe4 film was significantly higher than that of organic/inorganic composite films based on carbon nanotubes or metallic nanowires. The semiconductor transport characteristics of Ta4SiTe4 itself, combined with its one-dimensional structure, jointly contributed to the superior electrical transport performance described above.

While achieving excellent electrical transport performance, the organic/inorganic composite film formed by dimension-matched PVDF and Ta4SiTe4 also exhibits good flexibility. After being repeatedly bent 5,000 times on a curved surface with a diameter of 9 mm, the resistance of the PVDF/50 wt% Ta4SiTe4 film showed no significant change. The research team has initially fabricated a prototype thermoelectric device comprising four PVDF/50 wt% Ta4SiTe4 thermoelectric couples. At a temperature difference of 35.5 K, the device achieved a normalized maximum power density of 0.13 Wm⁻¹, representing the highest value reported to date for flexible thermoelectric devices.

The research was funded and supported by the National Key R&D Program, the National Natural Science Foundation of China, the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the Shanghai Young Science and Technology Star Program.

Article link: https://doi.org/10.1039/c9ee03776d

Figure a) Schematic illustration of the flexible composite film PVDF/Ta4SiTe4. b) Comparison of thermoelectric performance between the PVDF/Ta4SiTe4 composite film and previously reported one-dimensional organic-inorganic composite films. c) Comparison of normalized maximum power density between the PVDF/Ta4SiTe4-based prototype thermoelectric device and previously reported flexible thermoelectric devices.

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