Thermo-Electrochemical Cells Based on Carbon Nanotube Electrodes by Electrophoretic Deposition

Nano-Micro Letters, Jan 2016

Drawbacks of low efficiency and high cost of the electrode materials have restricted the wide applications of the thermo-electrochemical cells (TECs). Due to high specific areas and electrical conductivities, the low cost multi-walled carbon nanotubes (MWNTs) are promising alternative electrode materials. In this work, the MWNT films of up to 16 cm2 were synthesized on stainless steel substrates by the electrophoretic deposition (EPD) to make the thermo-electrochemical electrodes. MWNT electrodes based on TECs were characterized by cyclic voltammetry and the long-term stability tests with the potassium ferri/ferrocyanide electrolyte. The TECs reached the current density of 45.2 A m−2 and the maximum power density of 0.82 W m−2. The relative power conversion efficiency of the MWNT electrode is 50 % higher than that for the Pt electrode. Meanwhile, the TECs was operated continuously for 300 h without performance degradation. With the priorities of low cost and simple fabrication, EPD-based MWNT TECs may become commercially viable.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs40820-016-0082-8.pdf

Thermo-Electrochemical Cells Based on Carbon Nanotube Electrodes by Electrophoretic Deposition

Nano-Micro Lett. ( Thermo-Electrochemical Cells Based on Carbon Nanotube Electrodes by Electrophoretic Deposition Weijin Qian 0 1 . Mingxuan Cao 0 1 . Fei Xie 0 1 . Changkun Dong 0 1 0 Institute of Mirco-Nano Structure & Optoelectronics, Wenzhou University , Wenzhou 325035 , People's Republic of China 1 & Changkun Dong Drawbacks of low efficiency and high cost of the electrode materials have restricted the wide applications of the thermo-electrochemical cells (TECs). Due to high specific areas and electrical conductivities, the low cost multi-walled carbon nanotubes (MWNTs) are promising alternative electrode materials. In this work, the MWNT films of up to 16 cm2 were synthesized on stainless steel substrates by the electrophoretic deposition (EPD) to make the thermo-electrochemical electrodes. MWNT electrodes based on TECs were characterized by cyclic voltammetry and the long-term stability tests with the potassium ferri/ferrocyanide electrolyte. The TECs reached the current density of 45.2 A m-2 and the maximum power density of 0.82 W m-2. The relative power conversion efficiency of the MWNT electrode is 50 % higher than that for the Pt electrode. Meanwhile, the TECs was operated continuously for 300 h without performance degradation. With the priorities of low cost and simple fabrication, EPD-based MWNT TECs may become commercially viable. Thermo-electrochemical cells; Carbon nanotubes; Electrophoretic deposition 1 Introduction Harvesting of low grade heat (\130 C) is considered an effective sustainable energy source. Thermo-electrochemical cells (TECs) utilize the temperature-dependent electrochemical redox potentials to convert the thermal energy to electrical energy. Comparing with other thermal energy harvesting techniques, such as the thermoelectrics, thermocouples, and stirling engines [ 1–4 ], TECs have great potential for wide applications due to advantages of simple The authors Weijin Qian and Mingxuan Cao contributed equally to this work. design, maintenance-free, environment-friendly, and low cost. As shown in Fig. 1a, the two half cells of the TECs are held at different temperatures, causing a difference in the redox potential of the mediator around the anode and cathode [ 5 ]. Electrons are generated at the anode due to the oxidation reaction of ferrocyanide. When traveling through the cathode, electrons would be consumed from the reduction reaction of ferricyanide. The ingredient of the electrolyte keeps almost unchanged owing to the balance of oxidized and reduced species in the solution [ 5 ]. As a result, the current and output power can be acquired continuously. The electrode exchange current density is one of the most important factors in energy conversion for TECs. In practice, the current of TECs can be described from the relation: I = V/R, where V represents the voltage between the two working electrodes, and the resistance R consists of four parts, i.e., charge transfer, ohmic, solution diffusion, and thermal diffusion resistances [ 6, 7 ]. To get high exchange current densities, the redox couples, such as the ferri/ferrocyanide electrolyte, are commonly selected in TECs [ 8, 9 ]. In the selection of electrode materials, the (a) e− (d) Cr Fe C O Mg 0 1 2 3 4 5 1302 1304 1306 Binding energy (eV) fast charge transfer property and low resistance at the electrode/electrolyte interface are important factors. Platinum is the conventional electrode material due to high surface catalytic activity for oxidation and reduction reactions. However, it is hard to promote Pt-based TECs in engineering fields due to high cost and low conversion efficiency [ 6, 8 ]. With the development of nanotechnology [ 10–13 ], carbon nanotubes (CNTs) have been employed in different electrochemical devices [ 14–18 ], such as lithium-ion batteries, supercapacitors, and fuel cells due to large specific surface area and high catalytic activity. Recently, applications of MWNTs in TECs are widely investigated [ 19–23 ]. In the preparation of the MWNT electrode, the chemical vapor deposition (CVD) growth is widely applied [ 8, 9, 22 ]. The MWNT TECs electrodes prepared by CVD show promising electrical contact and stability properties. Electrophoretic deposition (EPD) is an effective technique to produce CNTs films with various advantages, including fewer requirements on the type & shape of the substrate, large-scale production capability, and low cost [ 24 ]. In this work, we prepared the TECs electrodes by EPD of MWNTs on metal substrates. The TECs presented excellent long-term operation stability and substantial higher energy conversion efficiency than that for Pt-based TECs. This investigation suggests that EPD method may be applicable for MWNTs-based TECs. 2 Experimental The MWNT material, with lengths from 10 to 30 lm, outer diameters of approximately 10 nm, and purity of [90 %, was purchased from XFNANO Materials. The MWNTs were first filtered and washed with acetone, then (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs40820-016-0082-8.pdf

Weijin Qian, Mingxuan Cao, Fei Xie, Changkun Dong. Thermo-Electrochemical Cells Based on Carbon Nanotube Electrodes by Electrophoretic Deposition, Nano-Micro Letters, 2016, pp. 240-246, Volume 8, Issue 3, DOI: 10.1007/s40820-016-0082-8