Phase, Morphology, and Particle Size Changes Associated with the Solid−Solid Electrochemical Interconversion of TCNQ and Semiconducting CuTCNQ (TCNQ = Tetracyanoquinodimethane)

Abstract

The origins of extensive solid−solid-state interconversions that accompany the electrochemistry of microparticles of tetracyanoquinodimethane (TCNQ) and semiconducting CuTCNQ (phases I and II) adhered to glassy carbon (GC) electrodes, in contact with CuSO4(aq) electrolyte, have been identified. Ex situ analyses with electron microscopy, infrared spectroscopy, and X-ray diffraction have been used to identify the phase changes that occur during the course of potential cycling or bulk electrolysis experiments. All redox-based transformations require extensive density, volume, and morphology changes, and consequently they are accompanied by crystal fragmentation. The net result is that extensive potential cycling ultimately leads to the thermodynamically favored TCNQ/CuTCNQ(phase II) solid−solid interconversion occurring at the nanoparticle rather than micrometer size level. The overall chemically reversible process is described by the reaction TCN + C + 2e- ⇌ CuTCNQ(S,GC)(phase I or phase II). Needle-shaped ...