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)