Fabrication of heteroatom-self-doped hierarchical porous carbon from soy protein isolate hydrogel for high-performance supercapacitors via a double-effect strategy of template-activation

The three-dimensional (3D) N/O/S self-doped hierarchical porous carbons (SPI-PC-x) with a “coral”-like geometry structure are successfully synthesized with renewable soy protein isolated (SPI) as the precursor. Draw support from the self-swelling principle of proteins, the SPI hydrogel is fabricated to absorb KOH solution, and thus uniformly distributed KOH not only serves as a built-in template to prevent carbon wall fusion/aggregation, but also acts as an activator to produce plentiful micropores. On the whole, our approach is sustainable because hierarchical porous carbons (PCs) are generated by a one-step pyrolysis process with a very low consumption of KOH. The SPI-PC-0.50 exhibits the gravimetric specific capacitance of 320 F g −1 at a current density of 0.5A g −1 in the threeelectrode system because of a great specific surface area (SSA) (1914.08 m 2 g −1 ) and a high heteroatom-doping level (16.4 at%). And it achieves the energy density of 8.0 Wh kg −1 and 27.0 Wh kg −1 in the two-electrode systems with 6 M KOH and 1 M Na 2 SO 4 as electrolytes, respectively. This work provides a theoretical and methodological support for the facile fabrication of 3D heteroatom self-doped PCs with the assistance of SPI gelation and the uniformly distributed activator under the principle of protein self-swelling. • An environment-friendly approach to fabricate PCs from SPI hydrogels was put forward. • KOH consumption for PC activation is much small. • KOH absorbed for activation also forms a template to prevent the structure collapse of PCs. • One-step pyrolysis is enough to guarantee the excellent electrochemical properties of PCs.