TY - JOUR
T1 - A fundamental study of the thermoelectrochemistry of ferricyanide/ferrocyanide
T2 - Cation, concentration, ratio, and heterogeneous and homogeneous electrocatalysis effects in thermogalvanic cells
AU - Buckingham, Mark A.
AU - Hammoud, Samer
AU - Li, Huanxin
AU - Beale, Conor J.
AU - Sengel, Jason T.
AU - Aldous, Leigh
PY - 2020/7
Y1 - 2020/7
N2 - Thermogalvanic cells typically utilise equimolar concentrations of the oxidised and reduced states of a redox couple in solution, sandwiched between two electrodes at dissimilar temperatures; entropy drives redox processes to occur at these electrodes, generating a potential difference and a current. However, significant gaps still exist in fundamental data and understanding of these 'thermocells'. In this study, thermocells based upon potassium ferricyanide, K3[Fe(CN)6], and potassium ferrocyanide, K4[Fe(CN)6], were investigated. The ratio of the oxidised and reduced states were systematically varied, and this had a significant effect upon the power produced; notably maximum power did not correspond to the equimolar ratio. A concentration study using equimolar ratios was also performed. Trends in the potential generated as a function of temperature (or 'Seebeck coefficient') were rationalised by the Nernst equation and Debye-Hückel theory. The trends in the current and the electrical power produced were successfully modelled using the Butler-Volmer equation. The effects of heterogeneous electrocatalysis were also explored (using platinum and two types of graphite) as well as homogeneous electrocatalysis, by the direct addition of alkali metal salts (as lithium, sodium, potassium, rubidium and caesium chlorides and sulphates). Clear trends were observed, and homogeneous and heterogeneous electrocatalysis had an additive effect when combined. Addition of CsCl was able to boost the maximum power output by upto ca. 80%, via both an increased Seebeck coefficient (through altered solvation) and through increased current (via homogeneous electrocatalysis of electron transfer). Finally, a limited economic comparison was performed, which highlights how the use of non-stoichiometric ratios of the redox couple could improve the cost-per-power value of the systems. This journal is
AB - Thermogalvanic cells typically utilise equimolar concentrations of the oxidised and reduced states of a redox couple in solution, sandwiched between two electrodes at dissimilar temperatures; entropy drives redox processes to occur at these electrodes, generating a potential difference and a current. However, significant gaps still exist in fundamental data and understanding of these 'thermocells'. In this study, thermocells based upon potassium ferricyanide, K3[Fe(CN)6], and potassium ferrocyanide, K4[Fe(CN)6], were investigated. The ratio of the oxidised and reduced states were systematically varied, and this had a significant effect upon the power produced; notably maximum power did not correspond to the equimolar ratio. A concentration study using equimolar ratios was also performed. Trends in the potential generated as a function of temperature (or 'Seebeck coefficient') were rationalised by the Nernst equation and Debye-Hückel theory. The trends in the current and the electrical power produced were successfully modelled using the Butler-Volmer equation. The effects of heterogeneous electrocatalysis were also explored (using platinum and two types of graphite) as well as homogeneous electrocatalysis, by the direct addition of alkali metal salts (as lithium, sodium, potassium, rubidium and caesium chlorides and sulphates). Clear trends were observed, and homogeneous and heterogeneous electrocatalysis had an additive effect when combined. Addition of CsCl was able to boost the maximum power output by upto ca. 80%, via both an increased Seebeck coefficient (through altered solvation) and through increased current (via homogeneous electrocatalysis of electron transfer). Finally, a limited economic comparison was performed, which highlights how the use of non-stoichiometric ratios of the redox couple could improve the cost-per-power value of the systems. This journal is
UR - http://www.scopus.com/inward/record.url?scp=85088260140&partnerID=8YFLogxK
U2 - 10.1039/d0se00440e
DO - 10.1039/d0se00440e
M3 - Article
AN - SCOPUS:85088260140
SN - 2398-4902
VL - 4
SP - 3388
EP - 3399
JO - Sustainable Energy and Fuels
JF - Sustainable Energy and Fuels
IS - 7
ER -
