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 Cu2+ 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”.

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► The EPR spectroscopy showed that copper in Cu-ZSM5 is as isolated form of Cu2+ ions.
► Electrochemical reduction of Cu2+/Cu0 occurs by two steps due to stabilization of Cu+.
► Stabilization is associated to interactions Cu+/C  C group and the zeolite framework.
► Redox processes Cu2+ to Cu+ and Cu+ to Cu0 occurs at nitrate- and sulfate solutions.