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Hierarchically porousc arbon (HPC)d erived from fallen flowers was prepared by ag reen method of combining solvent-freeb all milling with the safe activating agent potassium bicarbonate. By regulating the mass ratio of KHCO 3 to biochar,t he as-prepared HPC materials possess high specific surface areas of up to 2147.9 m 2 g À1 and abundant hierarchical pores comprised of micro-, meso-, and macropores.T he specific capacitanceso ft he HPC materials are able to reach3 02.7 Fg À1 at ac urrent density of 0.5 Ag À1 in 6 m KOH, and the symmetric supercapacitorc omposed of two identicalH PC electrodes shows good stability because 100 %o ft he specific capacitance is retained after 5000 charge/dischargec ycles and 90.5 %o ft he specific capacitance remainsa fter 12 000 cycles.N itrogen self-doped HPC materials also show higher electrocatalytic activity and stronger methanolt olerance for the oxygen reductionr eaction than that of the commercialP t/C catalyst. This preparation method can be extended to the green conversion of other varieties of biomass waste into usefulc arbon materials.

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Acting as an efficient metal-free ORR electrocatalyst, nitrogen-doped porous carbon derived from coconut mesocarp was prepared by a solvent-free ball-milling process.