Application of tetrafluoro-p-hydroquinone and 3-fluorocatechol as the catholyte and Cd nanoparticles as anolyte electroactive materials to manufacture of hybrid redox flow batteries

Abstract

The electrochemical reduction of oxidation products of tetrafluoro-p-hydroquinone, TFQH2, and 3-fluorocatechol, 3FQH2, in a 1.0M sulfuric acid solution is used as the positive electrode reaction to manufacture of hybrid redox flow batteries, HRFBs. Our previous studies and the results of this manuscript demonstrate that the electrochemical oxidation products 3FQH2 and TFQH2 are stable at time window of the cyclic voltammetric method as well as under different applied experimental conditions. Also, TFQH2 is a suitable compound for manufacturing of HRFBs. This is due to the stability of the electrochemical oxidation product of TFQH2 at time window of the electrolysis process. In addition, oxidation of electrodeposited cadmium on the copper electrode surface is used as the negative electrode reaction. Galvanostatic charge-discharge cycles are performed to determine the energy and coulombic performances of these compounds when they are used as active materials in fabrication of HRFBs. The proposed HRFBs were frequently charged and discharged in a voltage range of 0.8 to 1.6V. The results demonstrate stable charge-discharge cycling over 40cycles with the energy efficiency of 80% and a negligible capacity loss at room temperature for TFQH2. According to the experimental results, although the difference between the formal redox potential of 3FQH2 and cadmium is greater than that of TFQH2 and cadmium, the coulombic and energy efficiencies of an HRFB including TFQH2 is significantly higher than those of one including 3FQH2. Finally, TFQH2 is proposed as an excellent electroactive material for fabrication of an HRFB.