(Nanocarbons Division Poster Award, 3rd Place) Hybrid Supercapacitance and Stability of Fe-Based Metal-Organic Frameworks/Graphene Oxide Nanoribbons Composite Allover the pH Range

Abstract

Adopting renewable energy sources is growing fast, and hence it should be accompanied by tremendous efforts to develop energy storage technologies that can mitigate the intermittent nature of these sources. Supercapacitors (SCs) are considered among the most promising technologies for that purpose due to their high durability, power density, and charging/discharging competency. SCs have two types according to their electrochemical charge storage mechanism: pseudocapacitance (PCs) or battery-like behavior and electrochemical double-layer capacitors (EDLCs). The development of next-generation supercapacitors requires a holistic approach that integrates both mechanisms. Because of their huge surface area, porous structure, and abundance of active redox sites, metal-organic frameworks (MOFs) have exceptional potential in energy storage devices. However, due to the MOFs’ low conductivity and stability, they are in need to be mixed with highly conductive and stable materials such as carbon-based ones.In this work, Fe-based MOFs were selected to be responsible for mainly the battery-like contribution to the overall supercapacitance due to the presence of the redox-active sites. Even though little attention has been given to the Fe-based MOFs they showed a promising performance in several solutions, with low stability.1,2 To enhance the Fe-MOFs stability and conductivity and add an EDLC component to the overall capacitance behavior graphene oxide nanoribbon (GONRs) was used. The GONRs' exceptional properties such as ultrathin two-dimensional structures, superior mechanical behavior, strong chemical stability, and high electrical conductivity make them promising materials for supercapacitor applications.In this study, Fe-MOFs were synthesized using a hydrothermal method,3 and GONRs were prepared using an oxidative unzipping method.4 A composite of Fe-MOFs/GONRs was prepared by physical mixing. The physical and chemical properties of the synthesized Fe-MOFs, GONRs, and Fe-MOFs/GONRs were characterized using XRD, SEM, TEM, FT-IR, Raman spectroscopy, and XPS. Since the electrolyte properties have a substantial impact on the supercapacitive behavior and stability of the electrode materials, the specific capacitance of the prepared composites was measured in 1M H2SO4, 1M KOH, 1M K2SO4, and 1M KCl utilizing different evaluation systems (three and two-electrode systems). The Fe-MOFs/GONRs composite showed a significant synergistic effect in comparison to its pure components. Further discussion will be given regarding the pH and ion size/type effect on the supercapacitive performance and stability.