Metal center dependent electrochemical behavior of covalently functionalized graphene oxide phthalocyanine hybrids in symmetric supercapacitors

Abstract

Understanding the role of metal centers in interfacial charge storage remains an important issue in the development of graphene-based energy storage materials. In this study, graphene oxide was covalently functionalized with cobalt and nickel-centered phthalocyanine conjugates through ester linkages, yielding two nanohybrids with comparable structural frameworks but different metal centers. This approach allows a direct comparison of metal-dependent electrochemical responses under symmetric two-electrode conditions. Spectroscopic analyses, including FT-IR, Raman, and X-ray photoelectron spectroscopy, support the formation of covalent linkages while indicating that the structural features of both graphene oxide and phthalocyanine units are largely preserved. Electrochemical measurements reveal that the charge storage behavior depends on the nature of the metal center. The GO-CoPc hybrid shows a higher contribution from faradaic processes at low current densities, which can be associated with accessible cobalt redox transitions. In contrast, the GO-NiPc hybrid exhibits a more capacitive response with lower polarization and improved rate performance, suggesting more efficient charge transport at the interface. Both materials were evaluated in an aqueous KOH electrolyte within the studied potential range, where a maximum specific capacitance of 132 F g-1 was obtained for GO-CoPc. The hybrids retain 90 percent of their initial capacitance after 1000 charge-discharge cycles. These results indicate that covalent functionalization of graphene oxide with phthalocyanine units provides a useful framework for examining how metal centers influence charge storage behavior in such systems.