Trosheva Maria A, Buckingham Mark A, Aldous Leigh
Department of Chemistry, King's College London Britannia House London SE1 1DB UK
Chem Sci. 2022 Apr 5;13(17):4984-4998. doi: 10.1039/d1sc06340e. eCollection 2022 May 4.
Harvesting wasted thermal energy could make important contributions to global energy sustainability. Thermogalvanic devices are simple, chemistry-based devices which can convert heat to electricity, through facile redox chemistry. The efficiency of this process is the ratio of electrical energy generated by the cell (in Watts) to the quantity of thermal energy that passes through the cell (also in Watts). Prior work estimated the quantity of thermal energy passed through a thermocell by applying a conductive heat transfer model to the electrolyte. Here, we employ a heat flux sensor to unambiguously quantify both heat flux and electrical power. By evaluating the effect of electrode separation, temperature difference and gelation of the electrolyte, we found significant discrepancy between the estimated model and the quantified reality. For electrode separation, the trend between estimated and measured efficiency went in opposite directions; as a function of temperature difference, they demonstrated the same trend, but estimated values were significantly higher. This was due to significant additional convection and radiation contributions to the heat flux. Conversely, gelled electrolytes were able to suppress heat flux mechanisms and achieve experimentally determined efficiency values in excess of the estimated values (at small electrode separations), with partially gelled systems being particularly effective. This study provides the ability to unambiguously benchmark and assess the absolute efficiency and Carnot efficiency of thermogalvanic electrolytes and even the whole thermocell device, allowing 'total device efficiency' to be quantified. The deviation between the routinely applied estimation methodology and actual measurement will support the rational development of novel thermal energy harvesting chemistries, materials and devices.
收集废热能量可为全球能源可持续性做出重要贡献。热动电装置是基于化学的简单装置，可通过简便的氧化还原化学过程将热能转化为电能。此过程的效率是电池产生的电能（以瓦特为单位）与通过电池的热能数量（同样以瓦特为单位）的比值。先前的工作通过将传导传热模型应用于电解质来估算通过热电池的热能数量。在此，我们使用热通量传感器来明确量化热通量和电功率。通过评估电极间距、温差和电解质凝胶化的影响，我们发现估算模型与量化现实之间存在显著差异。对于电极间距，估算效率与测量效率之间的趋势方向相反；作为温差的函数，它们呈现相同趋势，但估算值显著更高。这是由于热通量存在显著的额外对流和辐射贡献。相反，凝胶化电解质能够抑制热通量机制，并在实验确定的效率值超过估算值（在小电极间距情况下），部分凝胶化系统尤其有效。这项研究提供了明确基准和评估热动电电解质乃至整个热电池装置的绝对效率和卡诺效率的能力，从而能够量化“总装置效率”。常规应用的估算方法与实际测量之间的偏差将有助于合理开发新型热能收集化学、材料和装置。
