Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Summary

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Abstract

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (T_H, ~40-90 °C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a T_H = 70 °C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

Introduction

Ubiquitous low-grade heat energy (<100 °C) could be recycled and converted into electricity^1,2 but is instead wasted. Unfortunately, heat recovery is still a great challenge, because converting low-grade heat to electricity is usually inefficient due to the low temperature differential and the distributed nature of the heat sources³. Intensive research has been conducted in solid-state thermoelectric (TE) materials and devices for the past decades, but the scalable application of TE devices in a low-grade heat regime is limited by the low energy conversion efficiency (η....

Protocol

1. Preparation of the graphene oxide electrode

1. Synthesis of graphene oxide via the modified Hummer's method
   1. Steps 1.1.2 and 1.1.3 occur at a low temperature (<0 °C). Circulate ice water flowing through the external layer of a double wall glass beaker placed on a magnetic stirrer to create low temperature conditions for the reactants inside.
   2. Mix 1 g of sodium nitrate (NaNO₃) with 100 mL of sulfuric acid (H₂SO₄, reagent grade, 95-98%) using slow stirring in the beaker.
   3. Add 1 g of flake graphite into the sulfuric acid and stir for 1 h in the cold bath. Add 6 g of potassium permang....

Results

The aTEC pouch cell was configured with asymmetric electrodes consisting of a GO cathode, a PANI anode, and filled with the KCl electrolyte. The thickness of the pouch cell shown in Figure 1A is 1 mm, which facilitates isothermal conditions between the two electrodes as well as efficient heat conduction. The scanning electron microscopy (SEM) images of the GO cathode and the PANI anode coated on carbon paper are shown in .......

Discussion

The aTEC converts thermal energy into electricity via a thermal charging process when heating from RT to T_H and a successive electrical discharging process at T_H. Getting rid of the dependence on a temperature gradient or a temperature cycle like the TGC and TREC, aTEC allows isothermal heating operation during the entire charging and discharging processes. Thermal induced voltage is based on the pseudocapacitive effect of GO because heating facilitates the chemisorption of protons on the oxygen fun.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Alumina laminated film	Showa Denko	SPALF C4
Carbon black	Alfa Aesar	H30253.22
Carbon paper	CeTech Co. Ltd	W0S1009
Carboxymethyl cellulose (CMC)	Guidechem company
DC Power supply	B&K Precision	Model 913-B
Doctor blade coater	Shining Energy Co. Ltd
Gamry	Gamry Instruments	Reference 3000
Graphite	Sigma-Aldrich	332461-2.5KG
Mixer	Thinky	ARE-250
Nickel tab	Tianjin Iversonchem company		4 mm width
N-Methyl-2-pyrrolidone (NMP)	Sigma-Aldrich	443778-1L
Polyaniline (leucoemeraldine base)	Sigma-Aldrich	530670-5G
potassium permanganate (KMnO4)	Sigma-Aldrich	223468-500G
Separator	CLDP		25 um thickness
Sodium nitrate (NaNO3)	Sigma-Aldrich	S5506-250G
Styrene butadiene	Tianjin Iversonchem company	BM400
Sulfuric acid	Sigma-Aldrich	320501-2.5L
Thermoelectric modules	CUI Inc.	CP455535H
Titanum foil	Qingyuan metal		0.03 mm thickness