Understanding electrochemical stability of Cu⁺ on zeolite modified electrode with Cu-ZSM5

In the present work the system Cu-ZSM5 was prepared by aqueous ion-exchange method from zeolite H-ZSM5. The solids were characterized by X-ray diffraction, nitrogen physisorption, temperature-programmed reduction with hydrogen (TPR-H₂) and electron paramagnetic resonance (EPR). These porous materials were mixed with poly (methacrylic acid methyl ester) and methyl acrylate (MA), and immobilized on a glassy carbon electrode in order to obtain the so-called zeolite-modified electrode (ZME). The as-prepared electrodes were characterized by infrared spectroscopy and electrochemical techniques as cyclic voltammetry and chronocoulometry. The presence of copper in the zeolite was confirmed by TPR-H₂. The XRD results indicate not important structural changes in the zeolite ZSM5 due to copper incorporation. The EPR spectroscopy showed that copper in Cu-ZSM5 is as isolated form of Cu ²⁺ ions. The results of nitrogen physisorption suggest that the Cu²⁺ cations are occupying the exchange sites in zeolite ZSM5. On the other hand, the IR spectroscopy revealed the presence of C O and C C groups in the mixture Cu-zeolite/polymer. The electrochemical profiles showed that reduction of Cu²⁺ to Cu⁰ occurs by two steps in presence of chloride due to stabilization of Cu⁺. The influence of anion in the electrolyte suggests that the redox processes Cu²⁺ to Cu ⁺ and Cu⁺ to Cu⁰ occurs on the zeolite-modified electrode even at nitrate- and sulfate-based solutions at the glassy carbon/zeolite interface. This stabilization is mainly associated to the interactions between Cu⁺ and C C group and the zeolite framework acting as "electron reservoir".