Pseudocapacitive behavior modulation and energy storage optimization via nitrogen-molybdenum co-doping in coconut shell-derived porous activated biochar

Abstract

The fabrication of electrode materials through heteroatom doping in carbon matrices serves as an effective approach to enhance the capacitive performance of supercapacitors. In this work, we designed a nitrogen‑molybdenum co-doped coconut shells porous activated biochar (CPB) via sequential carbonization, chemical activation, and doping processes. Comprehensive material characterization—including scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS)—revealed critical structure-property relationships. Nitrogen doping introduced electroactive pyridinic and pyrrolic nitrogen sites, significantly boosting pseudocapacitance. Meanwhile, molybdenum doping acted dualistically: it templated mesopore formation and generated molybdenum oxides, nitrides, and carbides within the carbon matrix during high-temperature treatment. These heterophases synergistically enhanced graphitic microcrystallite alignment, as evidenced by crystallographic analyses. Brunauer-Emmett-Teller (BET) measurements confirmed hierarchical porosity in CPB-KNM800, exhibiting a high specific surface area (1263.4 m²·g⁻¹) with 89 % micropore volume. This multiscale pore architecture facilitated rapid ion transport, as demonstrated by electrochemical testing. Electrochemical tests were performed under a three-electrode system (Hg/HgO), and the specific capacitance reached a maximum of 450 F g⁻¹ at a current density of 1 A g⁻¹, and exhibited outstanding cycling stability with 94 % capacity retention after 5000 cycles at a high current density of 10 A g⁻¹.