Self-assembled monolayer conducting polymer film/metal composite electrocatalysts: Electrolysis and direct methanol fuel cell applications

In this study, the aim was to prepare a multifunctional, highly catalytic, stable over time, and cost-effective new organic-metal composite thin film that can be used as both a cathode in electrolysis systems and an anode in fuel cells. To achieve this goal, films of the conductive polymer polyrhodanine (pRd) were prepared in two different ways on Pt and Cu surfaces and their electrocatalytic effects were investigated. Initially, a thin pRd film was synthesized on Pt using an electrochemical method. The synthesized film was mechanically removed from the surface, dissolved in ethanol, and Cu substrate was immersed in this solution for 24 hours to form a self-assembled monolayer (SAM) of a conductive polymer (Cu/pRd-SAM). Such a polymer SAM film on a metal surface was reported for the first time in the literature. Since it does not require any pre-passivation process, practical to apply, and the films are tightly adhered to the metal surface, the developed method offers significant advantages over other techniques. In the final stage of the study, a small amount of Pd was deposited on the surfaces of Pt/pRd and Cu/pRd-SAM (Pt/pRd/Pd and Cu/pRd-SAM/Pd) to further enhance their electrocatalytic effects. The prepared Cu/pRd-SAM and Cu/pRd-SAM/Pd electrodes were used as cathodes in a 6 M KOH solution, while Pt/pRd and Pt/pRd/Pd electrodes were used as cathodes in a 0.5 M H2SO4 solution, and their catalytic effects on hydrogen gas production were investigated using polarization, electrochemical impedance spectroscopy (EIS), and chronoamperometry techniques. Cu/pRd-SAM and Cu/pRd-SAM/Pd electrodes were used as anodes in a 1 M CH3OH containing 0.1 M KOH solution, while Pt/pRd and Pt/pRd/Pd electrodes were used as anodes in a 1 M CH3OH containing 0.5 M H2SO4 solution, and their suitability as anodes in direct methanol fuel cells was investigated using cyclic voltammetry (CV), EIS, and chronoamperometry techniques. The films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), and CV techniques. Homogeneous, tightly adhered pRd film with different colors at different thicknesses were synthesized on Pt surface. Using the proposed new method, purple-colored, highly homogeneous and tightly adhered pRd-SAM films were formed on the Cu surface. Pd was deposited homogeneously on pRd and pRd-SAM. Both non-deposited and deposited pRd and pRd-SAM modified electrodes showed excellent stability over time in electrolysis and direct methanol fuel cell systems. The electrodes catalyzed the rate of two reactions. The deposition of a small amount of Pd on the films further enhanced their catalytic performance. Therefore, it is suggested that Pt/pRd/Pd and Cu/pRd-SAM/Pd electrodes can be used as cathodes in electrolysis systems and as anodes in fuel cells.