Pressure-dependent self-template pyrolysis modulates the porosity and surface chemical configuration of carbon for potassium ion hybrid capacitors

Herein, a pressure-dependent self-template pyrolysis strategy is developed to modulate the porosity and surface chemical configuration of carbon electrodes (MPCs) for dual-carbon potassium ion hybrid capacitors (PIHCs). Experiments demonstrate that negative pyrolysis pressure (△P = −0.1 MPa) can restrict the growth of templates in the carbon matrix and accelerate surface oxygen removal, contributing to a large surface area of 2383.6 m2 g−1 with abundant micropores for high adsorption capacity and low surface oxygen content for good compatibility with the electrolyte at high voltage as cathodes. Relatively, positive pressure (△P = 10.0 MPa) prevents the escape of pyrolysis gas which would in turn re-react with the self-generated templates, thereby forming hierarchical macroporous structure composed of interconnected carbon nanosheets and nanoparticles for high-rate capabilities as anodes. As a result, NPC cathodes exhibit high capacity of 63.7 mA h g−1 after 8000 cycles at 2.0 A g−1, while PPC anodes deliver high capacity of 258.8 mA h g−1 with capacity retention of 93.5 % after 10,000 cycles at 5.0 A g−1. The assembled PPC//NPC PIHCs also exhibit high energy density of 172.8 Wh kg−1 at 223.1 W kg−1, with long-term cycling stability over 10,000 cycles at 1.0 A g−1 or 2.0 A g−1.