Interaction between copper and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) plays a crucial role in the performance of the DMcT-based polymer composite cathode with a copper current collector. In order to understand this interaction, we employed voltammetry combined with in situ electrochemical quartz crystal microgravimetry (EQCM) and in situ phase measurement interferometric microscope (PMIM), and investigated electrochemical behavior and surface morphologic changes of a copper substrate in nonaqueous solutions without and with DMcT. Voltammetric results show that DMcT inhibits electrodissolution of copper at potentials negative of 1.0 V vs. SSCE. EQCM results suggest that Cu may dissolve chiefly as Cu+, which may be stabilized by DMcT by forming a complex, at more positive potentials than 1.0 V. The PMIM images and corresponding data demonstrate that copper dissolution is a nonuniform process and results in a roughness increase of surface in the absence of DMcT while the presence of DMcT makes the substrate surface remain relatively smooth. Scanning electron micrographs further support the PMIM observations.Interaction between copper and 2,5-dimercapto-1,3,4-thiadiazole (DMcT) plays a crucial role in the performance of the DMcT-based polymer composite cathode with a copper current collector. In order to understand this interaction, we employed voltammetry combined with in situ electrochemical quartz crystal microgravimetry (EQCM) and in situ phase measurement interferometric microscope (PMIM), and investigated electrochemical behavior and surface morphologic changes of a copper substrate in nonaqueous solutions without and with DMcT. Voltammetric results show that DMcT inhibits electrodissolution of copper at potentials negative of 1.0 V vs. SSCE. EQCM results suggest that Cu may dissolve chiefly as Cu*, which may be stabilized by DMcT by forming a complex, at more positive potentials than 1.0 V. The PMIM images and corresponding data demonstrate that copper dissolution is a nonuniform process and results in a roughness increase of surface in the absence of DMcT while the presence of DMcT makes the substrate surface remain relatively smooth. Scanning electron micrographs further support the PMIM observations.