Contents
1. Introduction Page No.2
2. Development and application of the thermogalvanic
effect in the field of electrochemistry Page No.3
2.1. Working principle of redox reaction thermocouple Page No.3
2.2. Factors affecting thermocouples based on
thermogalvanic effect Page No.4
2.2.1. Impacts of hydrogel composition Page No.4
2.2.2. Impacts of structure design Page No.6
2.2.3. Impacts of electrode materials Page No.7
2.3. Application aspects and experimental scenarios
of thermogalvanic hydrogels Page No.7
2.3.1. Thermal induction self-supply equipments Page No.7
2.3.2. Integrated applications Page No.8
2.3.3. Heat collection and management devices Page No.9
3. Conclusions and Perspectives Page No.9
1. Introduction
With the exponential increase in energy demand, there has been an excessive reliance on fossil fuels such as natural gas, oil, and coal, resulting in severe pollution, widespread environmental damage, and further aggravation of the global energy crisis.[1-6] Therefore, the pursuit of energy recycling has gained significant attention. Heat energy, which is derived from the burning of fossil fuels or solar radiation, serves as a widely utilized energy source. While heat can be partially recycled, the challenge lies in effectively reusing and capturing low-order heat generated by human activities, solar radiation, and electronic devices.[7–11]
Solid-state thermoelectric devices based on semiconductors have been widely researched and applied for the recycling of low-grade thermal energy. Nonetheless, it is important to acknowledge that the output performance of these semiconductor devices is temperature-dependent. Excessively high temperatures pose a risk of fracture in the p-n junction, resulting in considerable deterioration in performance. Conversely, extremely low temperatures reduce the thermoelectric properties of solid materials, resulting in remarkably low Seebeck coefficients ranging from 100 to 200 µV K–1.[12,13] Currently, Bi2Te3 stands as the sole commercially utilized solid-state material in this domain. [14]Temperature fluctuations threaten the performance stability, safety, and lifespan of electronics. Thus, maximizing the efficiency of thermoelectricity and exploring new avenues for its development have become prominent areas of research. In this context, hydrogels have emerged as a promising electrolyte medium. Current studies indicate that hydrogels exhibit two distinct working modes for the thermoelectric effect: thermogalvanic effect and thermal diffusion effect. Table 1 provides a simple comparison of the two modes. Thermogalvanic effect is a cost-effective option that offers flexible structural designs. Recent studies suggest that hydrogels utilizing the thermoelectric current effect can achieve Seebeck coefficients exceeding 1 mV K–1.[15–22] Moreover, certain experimental samples can be coupled and integrated to achieve higher output voltages. This review primarily focuses on the discussion of hydrogels using redox reactions as a basis for thermoelectric devices. It aims to provide a comprehensive understanding of the fundamental principles, gel structures, and practical applications of such systems.