Exploratory experiments on effects from a phase transition are reported for a low-melting microcrystalline anthraquinone (N,N,N’,N’-tetraoctyl-2,6-diamino-9,10-anthraquinone or TODAQ). Data for the solid-liquid phase transition are obtained by differential scanning calorimetry, and then compared to data obtained by voltammetry. In preliminary electrochemical measurements, microcrystal deposits on a basal plane pyrolytic graphite electrode are shown to undergo a solid state 2-electron 2-proton reduction in contact to aqueous 0.1 M HClO4 with a midpoint potential Emid,solid = -0.24 V vs. SCE. The reduction mechanism is proposed to be limited mainly by the triple phase boundary line and some transport of TODAQ molecules towards the electrode surface for both solid and melt. A change in the apparent activation energy for this reduction is observed at 69 oC, leading to an enhanced increase in reduction current with midpoint potential Emid,liquid = -0.36 V vs. SCE. A change of TODAQ transport along the crystal surface for solid microcrystalline material (for the solid) to diffusion within molten microdroplets (for the liquid) is proposed. Upon cooling, a transition at 60 oC back to a higher apparent activation energy is seen consistent with re-solidification of the molten phase at the electrode surface. Differential scanning calorimetry data for solid TODAQ dry and for TODAQ in contact to aqueous 0.1 M HClO4 confirm these transitions.
|Journal||Journal of Solid State Electrochemistry|
|Publication status||Accepted/In press - 13 Nov 2019|
Marken, F., Jones, M., Ahn, S. Y., Forder, T., Blackburn, R., Fordred, P., & Bull, S. (Accepted/In press). Voltammetric Monitoring of a Solid-Liquid Phase Transition in N,N,N’,N’-Tetraoctyl-2,6-diamino-9,10-anthraquinone (TODAQ). Journal of Solid State Electrochemistry.