Abstract: An electrochemical cell used for in situ electron spin resonance (ESR) measurements nnder electrochemical excitation in aqueous solution was designed and fabricated. Taking the in situ ESR investigation of methylene blue solution and polypyrrole film modified electrode as examples,the characteristics of the cell has been examined. The experiments performed in this cell not only provide new information for electrochemical processes of the two systems but also show that this cell is resonably arrangeed and has the outstanding advantages of precise potential control of the working electrode, rapid response and high sensitivity. This ESR cell is much useful for observing the intermediates or short lived species produced electrochemically in aqueous solution or other systems with large dielectric constant. Meanwhile, it can be applied for in situ preparing and studying film modified electrodes under different conditions with very convenient operation.

Key words: Electron spin resonance, electrochemical cell, methylene polypyrrole, chemically modified electrode