High Thermal Gradient in Thermo-electrochemical Cells by Insertion of a Poly(Vinylidene Fluoride) Membrane

Abstract

Thermo-Electrochemical cells (Thermocells/TECs) transform thermal energy into electricity by means of electrochemical potential disequilibrium between electrodes induced by a temperature gradient (ΔT). Heat conduction across the terminals of the cell is one of the primary reasons for device inefficiency. Herein, we embed Poly(Vinylidene Fluoride) (PVDF) membrane in thermocells to mitigate the heat transfer effects - we refer to these membrane-thermocells as MTECs. At a ΔT of 12 K, an improvement in the open circuit voltage (Voc) of the TEC from 1.3 mV to 2.8 mV is obtained by employment of the membrane. The PVDF membrane is employed at three different locations between the electrodes i.e. x = 2 mm, 5 mm, and 8 mm where ‘x’ defines the distance between the cathode and PVDF membrane. We found that the membrane position at x = 5 mm achieves the closest internal ∆T (i.e. 8.8 K) to the externally applied ΔT of 10 K and corresponding power density is 254 nWcm−2; 78% higher than the conventional TEC. Finally, a thermal resistivity model based on infrared thermography explains mass and heat transfer within the thermocells.

Crosslinked thermoelectric hydro-ionogels: A new class of highly conductive thermoelectric materials

“…The lower output power as compared with our measured value may be attributed to lack of ionic liquid in their gel electrolyte. Hasan et al reported the maximum power output of 245 n W /m 2 in membrane-inserted thermoelectrochemical cells (MTECs) with Seebeck coefficient of 0.4 mV/K but still, leakage problem exists due to the liquid state of electrolytes [58]. Our measured value of Power output is close to their value with higher Seebeck coefficient of 1.38 mV/K and no leakage issue because of the solid state of X-TEHIG.…”

“…where ZT is figure of merit, S is Seebeck coefficient also called thermopower (VK -1 ), σ is electrical conductivity (S m -1 ), K is thermal conductivity (W/ (m K), T is absolute temperature (K) and S 2 σ is called power factor (Wm -1 K -2 ). In order to get high ZT, the materials must possess higher Seebeck coefficient and electrical conductivity along with lower thermal conductivity [6][7][8][9]. The higher values of Seebeck coefficient will be accompanied by high voltage output, high electrical conductivity will reduce the Joule heating, and lower thermal conductivity will maintain large temperature gradients in TE modules [10,11].…”

Synthesis, Analysis and Thermoelectrochemical Applications of Ionic Liquids

“…At this point, ILs' influence on the redox couples must be understood so can obtain higher Seebeck coefficients. In 1968, for the first time Cornwell, et al showed the use of ILs in TECs, but the ILs' effects were not fully understood [102]. In 1980, Chum, et al contributed with a similar study [103].…”

Operando MRI for quantitative mapping of temperature and redox species concentrations in thermo-electrochemical cells

“…While these are extremely useful and can be used to quantify the device performance, they provide little information on the processes occurring within the electrolyte and certainly no insights into spatial variations in the cell. Said and co-workers have used infrared thermal imaging to study the temperature distribution across thermocells incorporating polymer membranes [25], but these images could only provide the temperature across the outer surface of the device.…”