Maximizing pore and heteroatom utilization within N,P-co-doped polypyrrole-derived carbon nanotubes for high-performance supercapacitors

Abstract

Promoting the efficient utilization of both pores and heteroatoms remains a highly challenging endeavor, yet is of crucial significance to enhance the specific capacitance and energy density of carbon-based supercapacitors (SCs). Herein, a series of N,P-co-doped polypyrrole-derived carbon nanotubes (Px-ppyNTs) featuring a customized porous structure and doping level and intrinsically endowed with hollow cavities with tunable diameters were designed and synthesized via a strategic engineering approach. Benefiting from their regularly evolved physiochemical architecture, Px-ppyNTs served as a suitable platform to investigate the structure–property relationship between carbon-based materials and electrochemical capacitive behavior. Remarkably, the electrochemical surface area (ECSA) was proven to be critical to the reaction kinetics and resulted in the maximized utilization of both the porous structure and heteroatoms. The optimized ppyNT material with highest utilization of both the SSA (1853 m² g⁻¹) and inherent heteroatom doping (nitrogen: 7.2 at% and phosphorous: 2.5 at%) exhibited an extremely high specific capacitance of 438 F g⁻¹ in 1.0 M H₂SO₄ and energy density of 25.3 W h kg⁻¹ in 1.0 M Na₂SO₄. Furthermore, the calculated electric double layer capacitance (EDLC) contribution was maintained at as high as 203 F g⁻¹ even across a wide scan rate in the range of 5 to 500 mV s⁻¹. This work affords a promising electrode material for SCs and provides new insights into the critical role of ECSA in high-performance carbon-based SCs.