The thermoelectrochemistry of the aqueous iron( ii )/iron( iii ) redox couple: significance of the anion and pH in thermogalvanic thermal-to-electrical energy conversion

Thermogalvanic conversion of temperature gradients into electricity via a redox couple represents a potential method of waste energy harvesting, but inexpensive, effective and sustainable redox couples are required. In this study four aqueous Fe( ii )/Fe( iii ) salt systems are considered, based upo...

Full description

Saved in:
Bibliographic Details
Published in:Sustainable energy & fuels 2018, Vol.2 (12), p.2717-2726
Main Authors: Buckingham, Mark A., Marken, Frank, Aldous, Leigh
Format: Article
Language:English
Subjects:
Acidification
Ammonium
Electrochemical impedance spectroscopy
Electrochemistry
Energy
Energy conversion
Energy harvesting
Iron
Iron sulfates
Nitrates
Organic chemistry
pH effects
Redox properties
Seebeck effect
Spectroscopy
Spectrum analysis
Sulfates
Sustainable harvest
Temperature effects
Temperature gradients
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Thermogalvanic conversion of temperature gradients into electricity via a redox couple represents a potential method of waste energy harvesting, but inexpensive, effective and sustainable redox couples are required. In this study four aqueous Fe( ii )/Fe( iii ) salt systems are considered, based upon ammonium iron sulphate, iron sulphate, iron trifluoromethanesulfonate and iron nitrate. A range of Seebeck coefficients were observed, from +0.18 ± 0.04 mV K −1 for ammonium iron( ii / iii ) sulphate to +1.46 ± 0.02 mV K −1 for acidified iron( ii / iii ) trifluoromethanesulfonate, both at a temperature difference of 20 K; notably these apparent Seebeck coefficients vary with temperature difference due to significant chemical equilibria. The iron( ii / iii ) nitrate system generated the highest thermogalvanic power output. The systems were probed by cyclic voltammetry, pH, UV-Vis spectroscopy and electrochemical impedance spectroscopy, and two competing mechanisms noted, which strongly affect both the current output and Seebeck coefficient ( i.e. potential output) of their thermoelectrochemical cells (or thermocells). Green and economic consideration are important aspects if these systems are to be employed in harvesting low-grade heat energy at a larger scale; iron nitrate and acidified iron sulphate were the most highly competitive systems.
ISSN:2398-4902
2398-4902
DOI:10.1039/C8SE00416A