水热法制备三维导电石墨烯气凝胶及其焦耳热性能研究

Joule-heating studies of electrically conducting three-dimensional graphene aerogels prepared by hydrothermal assembly

采用水热法将氧化石墨烯(GO)组装成三维圆柱状结构,通过冷冻干燥和高温热还原法成功制备三维导电的还原氧化石墨烯气凝胶。该气凝胶内部的高度交联和多孔道网状结构为电子传输提供有效路径,利于系统的焦耳热研究。结果表明,通过对其进行电流加热,石墨烯气凝胶表现出高功率-温度线性相关性、高电热转换效率、超快升温和降温速率、长时间且稳定的循环加热能力。通过不同模型验证了气凝胶内部可进行焦耳热传导,其高电导率主要由材料自身较低的活化能所决定。石墨烯气凝胶超高的热导率赋予其超快的自然降温速率(456 K∙min−1),远高于传统的热传导加热装置。此外,所制备的气凝胶还可被广泛应用于焦耳热辅助的催化剂温度可控的载体。

Joule-heating studies of different electric-conducting nanocarbon aerogels have been extensively exploited, however, there are no systematic investigations on the Joule-heating characteristics of reduced graphene oxide (rGO) aerogels prepared via the hydrothermal approach. Therefore, this work adopted the hydrothermal and freeze-drying methods, followed by thermal reduction to fabricate three-dimensional, cylindrical, and electric conducting reduced hydrothermal graphene oxide aerogel, i. e., rHT-GO aerogel. Electron microscopic analysis showed that the aerogel interior presented a high density of nanocarbon interconnectivity and multiscale porosity, providing numerous paths for electrons to transport, hence available for systematic Joule-heating studies. The results demonstrated that the power input and Joule-heating temperature exhibited a good linear correlation with R2 > 0.999, high electrothermal transformation efficiency (reaching up to 128℃ with only 2 W energy consumption), ultrafast heating/cooling capacities, long-duration electrothermal performance and excellent cycling capability. The 3D variable range hopping (3D VRH) model elucidated that the Joule-heating effects can reach the entire rHT-GO aerogel. The high electrical conductivity (9.0 S ∙ m−1) was originated from the small bandgap (Ea = 0.015 eV). Additionally, the radial temperature gradient fitting results corroborated that the as-prepared rHT-GO aerogels also displayed distinct thermal conductivity (0.222 W∙m−1∙K−1), resulting in their ultrafast cooling rates (456 K∙min−1) and consequently outperforming traditional external radiative heating modes. Importantly, the as-prepared cylindrical rHT-GO aerogels in this study can also be potentially utilized as Joule-heating-assisted adsorption/ desorption agents, energy-efficient heaters, temperature-controllable catalyst supports, highly accurate sensors, and solar water evaporators.