Graphitic Carbon Nitride: An Excellent Base for Composite Electrodes in Electrochemical Energy Conversion and Storage

Abstract

Growing environmental concerns linked with global energy demands have increased the need for sustainable, reliable and portable energy supply that can be delivered from energy conversion to energy storage. Although some emerging electrocatalysts can potentially compete with commercial electrocatalysts in terms of cost per unit kWh when using low-cost precursors to create them, research efforts are still mainly focusing on performance rather than cost. It is expected that flexible energy storage devices with multifunctionalities would spearhead the power management of future energy devices, which requires engineering solutions of volume and weight reduction. Nanocomposites that offer simultaneous energy conversion and storage capabilities with mechanical load bearing are promising candidates to provide these desired functionalities in electrochemical devices. Utilizing hierarchical porous polymers with combined properties of light weight, flexibility and absorption capacity offers numerous possibilities for the development and utilization of nanocomposites in applications ranging from electronics, aerospace, military to transportation where rapid or stored burst of energy is required for peak power, backup power and load levelling to achieve improved efficiency and reliability.In this work, iron oxide nanoparticles encapsulated in graphitic carbon nitride shells (Fex-NC) were grown on interconnected, macroscopic carbon scaffold after dip coating followed by carbonization to attain multifunctional nanocomposites. The resulting composites based on the graphitic carbon nitride base possess combined properties of superb structural flexibility, high strength to weight ratio and mechanical stability. The Fex-NC nanocomposites were tested for energy conversion and storage, to take advantage of their porous graphitic carbon nitride features which would be beneficial for optimal ion transport to iron oxide nanoparticles. We have found that the resulting graphitic carbon nitride shells prevented direct contact between iron oxide nanoparticles and acidic electrolyte (H2SO4), so that improved efficiency, stability and corrosion resistance were achieved. They also exhibit excellent electrochemical performances with overpotentials of 191 mV to reach current density of 10 mA/cm2 for hydrogen evolution reaction. In addition to demonstrating excellent specific capacitance, these nanocomposites also possess good stability after 8 hours of testing. The results demonstrate that the physicochemical properties of multifunctional 3D foams developed from simultaneous carbonization and dip coating of polymeric templates can be used as an excellent base to host a variety of nanoparticles to create composite electrocatalysts and be further exploited for future energy and environmental technologies.