Development andcharacterization of activated carbon / transition metal phosphide composites for electrochemical capacitors

2019-09-11
Electrochemical capacitors are the energy storage devices based mainly on electrical double layer formation. Their power densities are exceptionally high; however, their energy densities are characteristically low to compete various types of batteries in market. Therefore, there have been great amount of studies to enhance electrochemical capacitors’ energy density. Utilization of inorganic materials such as transition metal oxides and/or phosphides is one of the most common strategies to increase energy density. These materials generally bring about faradaic reactions at the electrode surface, increasing the energy storage capability. Transition metal phosphides are versatile materials both used in electrochemical capacitor studies and catalysis research for electrochemical water splitting [1]. They react with OH- ions in the alkaline electrolyte like transition metal oxides; however, their electrical conductivities are generally higher compared to that of oxides. This character provides better power densities in electrochemical capacitors compared to the oxides. Although the most widely used phosphide is Ni2P for both electrochemical capacitor and catalysis research, Cu and Co phosphides are argued to be promising [2]. In this study, activated carbon / transition metal phosphide composites were produced and utilized in the electrochemical capacitors. Activated carbons were produced using phosphoric acid impregnation. After they were produced, a second impregnation step was conducted to obtain phosphide particles on AC’s. In alkaline electrolyte, both electrical double layer on the surface of AC’s, and faradaic reactions on metal phosphides contribute to total capacitance. The microstructure of the AC/Cu3P composite is given in Figure 1. Figure 1. SEM micrograph of AC/Cu3P composite. XRD diffractogram of AC/Cu3P composite is given in Figure 2. As seen in the diffractogram, there is a broad hump between 15-30 degrees, characteristic of amorphous carbonaceous materials. Also, there are peaks at certain 2θ degrees, indicating presence of Cu3P phase. Figure 2. XRD diffractogram of AC/Cu3P composite. After the structural and morphological characterization of the composites, FTIR was conducted to the samples to understand the role of phosphate groups in transition metal phosphide formation. Then, electrochemical characterization was applied to measure capacitive properties of the composites. Also, electrical conductivities of the samples were measured and matched with the impedance properties of the materials
Citation Formats
K. Ö. Köse and M. K. Aydınol, “Development andcharacterization of activated carbon / transition metal phosphide composites for electrochemical capacitors,” presented at the mESC-IS 2019 : The Fourth International Symposium on Materials for Energy Storage and Conversion, 11-13 September 2019, 2019, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/87267.