Self-generation of low ash carbon microspheres from the hydrothermal supernatant of anaerobic digestate: Formation insights and supercapacitor performance

• Spherical carbon product self-generated from hydrothermal supernatant. Self-generated lower in inorganic content than carbon. Different 13 C NMR spectra to precursor indicating new formation. Activated stable under electrochemical cycling (>20000 cycles). Retention of high levels nitrogen (>6 at%). This work provides the first observations and insights into self-generation microspheres supernatant after carbonization anaerobic digestate has been completed hydrochar removed. Solid State XPS revealed that were comprised decomposed fragments proteins, carbohydrates lignin. The significantly ash (3.1%), compared solid (41.2%) (25.2%) their formation reduced total organic load low allowed them be easily activated, achieving a surface area 1711.0 m 2 g ?1 , 51.4 for activated 12.8 precursor. microcarbon spheres achieved specific capacitance cyclic voltammetry 86 F at 100 mV s 176 1 while gravimetric was 42 25 A 140 0.5 M Li SO 4 1.8V potential window. Overall, this study highlights importance exploring its valorisation ash-rich precursors.