1 SCIENTIFIC REPORTS | 6:29328 | DOI: 10.1038/srep29328 www.nature.com/scientificreports High Thermal Gradient in Thermo- electrochemical Cells by Insertion of a Poly(Vinylidene Fluoride) Membrane Syed Waqar Hasan 1 , Suhana Mohd Said 1 , Mohd Faizul Mohd Sabri 2 , Ahmad Shuhaimi Abu Bakar 3 , Nur Awanis Hashim 4 , Megat Muhammad Ikhsan Megat Hasnan 1 , Jennifer M. Pringle 5 & Douglas R. MacFarlane 6 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 (V oc ) 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. ermoelectricity, a phenomenon where a temperature gradient is converted into electricity, is a topic of intense research interest primarily for energy harvesting applications. A conventional thermoelectric (TE) module con- sists of an array of p- and n- type semiconducting materials assembled between two electrodes maintained at different temperatures. e efficiency of a typical TE device is governed by the temperatures of the hot and cold electrodes ( and Tc) as well as the intrinsic properties of TE materials. us, a dimensionless figure of merit (ZT) is defined by equation (1) as a quantitative measure of energy conversion capability of TE materials (p- and n- type materials). σ α =       ⋅ +       ⋅ ZT K K T (1) elec latt 2 where “σ” is electrical conductivity (S/m), “α” is the thermoelectric, or “Seebeck”, coefficient (V/K), “T” is the absolute temperature (K) while K elec and K latt are the electronic and lattice contribution of thermal conductivity (W/m·K) of the material, respectively 1–4 . erefore, the overall device efficiency (η) in the literature 3–4 is expressed as: 1 Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. 2 Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. 3 Low Dimensional Materials Research Centre, Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. 4 Department of Chemical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. 5 ARC Centre of Excellence for Electromaterials Science, Deakin University, Burwood, Victoria 3800, Australia. 6 ARC Centre of Excellence for Electromaterials Science, School of Chemistry, Monash University, Clayton, Victoria 3800, Australia. Correspondence and requests for materials should be addressed to S.M.S. (email: smsaid@um.edu.my) Received: 27 April 2016 Accepted: 15 June 2016 Published: 06 July 2016 OPEN