TY - JOUR
T1 - Nonadditivity of faradaic currents and modification of capacitance currents in the voltammetry of mixtures of ferrocene and the cobaltocenium cation in protic and aprotic ionic liquids
AU - Shiddiky, Muhammad Johirul Alam
AU - Torriero, Angel Alberto Jesus
AU - Zhao, Chuan
AU - Burgar, Iko
AU - Kennedy, Gareth Francis
AU - Bond, Alan Maxwell
PY - 2009
Y1 - 2009
N2 - Unexpected nonadditivity of currents encountered in the electrochemistry of mixtures of ferrocene (Fc) and cobaltocenium cation (Cc(+)) as the PF6_- salt has been investigated by direct current (dc) and Fourier-transformed alternating current (ac) cyclic voltammetry in two aprotic (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate) and three protic (triethylammonium formate, bis(2-hydroxyethyl)ammonium acetate, and triethylammonium acetate) ionic liquids (ILs). The voltammetry of the individual Fc(0/+) and Cc(+/0) couples always exhibits near-Nernstian behavior at glassy carbon and gold electrodes. As expected for an ideal process, the reversible formal potentials and diffusion coefficients at 23 +/- 1 degrees C in each IL determined from measurement on individual Fc and Cc(+) solutions were found to be independent of electrode material, concentration, and technique used for the measurement. However, when Fc and Cc(+) were simultaneously present, the dc and ac peak currents per unit concentration for the Fc(0/+) and Cc(+/0) processes were found to be significantly enhanced in both aprotic and protic ILs. Thus, the apparent diffusion coefficient values calculated for Fc and Cc(+) were respectively found to be about 25 and 35 larger than those determined individually in the aprotic ILs. A similar change in the Fc(0/+) mass transport characteristics was observed upon addition of tetrabutylammonium hexafluorophosphate (Bu4NPF6), and the double layer capacitance also varied in distinctly different ways when Fc and Cc(+) were present individually or in mixtures. Importantly, the nonadditivity of Faradaic current is not associated with a change in viscosity or from electron exchange as found when some solutes are added to ILs. The observation that the H-1 NMR T-1 relaxation times for the proton resonance in Cc(+) also are modified in mixed systems implies that specific interaction with aggregates of the constituent IL ionic
AB - Unexpected nonadditivity of currents encountered in the electrochemistry of mixtures of ferrocene (Fc) and cobaltocenium cation (Cc(+)) as the PF6_- salt has been investigated by direct current (dc) and Fourier-transformed alternating current (ac) cyclic voltammetry in two aprotic (1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate) and three protic (triethylammonium formate, bis(2-hydroxyethyl)ammonium acetate, and triethylammonium acetate) ionic liquids (ILs). The voltammetry of the individual Fc(0/+) and Cc(+/0) couples always exhibits near-Nernstian behavior at glassy carbon and gold electrodes. As expected for an ideal process, the reversible formal potentials and diffusion coefficients at 23 +/- 1 degrees C in each IL determined from measurement on individual Fc and Cc(+) solutions were found to be independent of electrode material, concentration, and technique used for the measurement. However, when Fc and Cc(+) were simultaneously present, the dc and ac peak currents per unit concentration for the Fc(0/+) and Cc(+/0) processes were found to be significantly enhanced in both aprotic and protic ILs. Thus, the apparent diffusion coefficient values calculated for Fc and Cc(+) were respectively found to be about 25 and 35 larger than those determined individually in the aprotic ILs. A similar change in the Fc(0/+) mass transport characteristics was observed upon addition of tetrabutylammonium hexafluorophosphate (Bu4NPF6), and the double layer capacitance also varied in distinctly different ways when Fc and Cc(+) were present individually or in mixtures. Importantly, the nonadditivity of Faradaic current is not associated with a change in viscosity or from electron exchange as found when some solutes are added to ILs. The observation that the H-1 NMR T-1 relaxation times for the proton resonance in Cc(+) also are modified in mixed systems implies that specific interaction with aggregates of the constituent IL ionic
UR - http://pubs.acs.org.ezproxy.lib.monash.edu.au/doi/pdf/10.1021/ja8092295
U2 - 10.1021/ja8092295
DO - 10.1021/ja8092295
M3 - Article
VL - 131
SP - 7976
EP - 7989
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 23
ER -