of polypyrrole and its derivatives. EQCM was used to study electro-polymerization process and doping/de-doping properties of polyaniline film on gold electrode surface as well. To investigate the electrosynthesis process, sometimes it is necessary to combine other characterization technologies, such as using FTIR and EQCM to study the effect of different conditions on the formation of poly(3,4-ethylenedioxythiophene) film structure, and using EQCM, together with AFM, FTIR, EIS, to investigate the film formation process in the alkyl carbonate/lithium salt electrolyte solution on precious metal electrodes surfaces. Application of EQCM in electrodeposition and dissolution EQCM is broadly used to study the deposition/dissolution process on electrode surface, such as the oscillation of electrode potential during Cu/CuO2 layered nanostructure electrodeposition, deposition growth process of cobalt and nickel hexacyanoferrate in calcium nitrate and barium nitrate electrolyte solution, and the Mg electrode electrochemical behaviour in various polar aprotic electrolyte solutions. EQCM can be used as a powerful tool for corrosion and corrosion protection study, which is usually combined with other characterization technologies. A previous work used EQCM and XPS studied Fe-17Cr-33Mo/ Fe-25Cr alloy electrodes mass changes during the potential sweep and potential step experiments in the passive potential region in an acidic and a basic electrolyte. Another previous work used EQCM and SEM to study the influence of purine (PU) on Cu electrode corrosion and spontaneous dissolution in NaCl electrolyte solution. Application of EQCM in adsorption and desorption EQCM has been used to study the self-assembled monolayers of long chain alkyl mercaptan and alkanethiol and mercaptoalkanoic on gold electrode surface. Application of EQCM in polymer modified electrode EQCM can be used to ideally modify polymer membranes together with other electrochemical measurements or surface characterization methods. A team has used CV, UV-Vis, IR and EQCM studied irreversible changes of some polythiophenes in the electrochemical reduction process in acetonitrile. Later on they used AFM and EQCM investigated growth of polypyrrole film in anionic surfactant micellar solution. Then combing with CV, UV-Vis, FTIR, ESR, they used EQCM to study conductivity and magnetic properties of 3,4-dimethoxy and 3,4-ethylenedioxy-terminated polypyrrole and polythiophene. Application of EQCM in energy conversion and storage EQCM can be used to study the process of adsorption and oxidation of fuel molecules on the electrode surface, and the effect of electrode catalyst or other additives on the electrode, such as assessment of polypyrrole internal Pt load in the polypyrrole/platinum composites fuel cell, methanol fuel cell anodizing process, and electrodeposition