In recent years, supercapacitors are leading among electrochemical energy storage devices since they can efficiently store energy produced from renewable energy sources. Moreover, supercapacitors attract more attention than batteries because of safety and numerous advantages over batteries as high power, instant charging, and long cycle life. Nowadays, metal phosphates have been attracting much attention for application in energy storage devices and catalysis due to their low cost, high conductivity, and redox reversibility. Besides such excellent properties, very few metal phosphate...