Reconfiguring the Electronic Structure of Heteroatom Doped Carbon Supported Bimetallic Oxide@Metal Sulfide Core–Shell Heterostructure via In Situ Nb Incorporation toward Extrinsic Pseudocapacitor

High-energy-density battery-type materials have sparked considerable interest as supercapacitors electrode; however, their sluggish charge kinetics limits utilization of redox-active sites, resulting in poor electrochemical performance. Here, the unique core–shell architecture of metal organic framework derived N–S codoped carbon@Co_xS_y micropetals decorated with Nb-incorporated cobalt molybdate nanosheets (Nb-CMO₄@C_xS_yNC) is demonstrated. Coordination bonding across interfaces and π–π stacking interactions between CMO₄@C_xS_y and N and, S–C can prevent volume expansion during cycling. Density functional theory analysis reveals that the excellent interlayer and the interparticle conductivity imparted by Nb doping in heteroatoms synergistically alter the electronic states and offer more accessible species, leading to increased electrical conductivity with lower band gaps. Consequently, the optimized electrode has a high specific capacity of 276.3 mAh g⁻¹ at 1 A g⁻¹ and retains 98.7% of its capacity after 10 000 charge–discharge cycles. A flexible quasi-solid-state SC with a layer-by-layer deposited reduced graphene oxide /Ti₃C₂T_X anode achieves a specific energy of 75.5 Wh kg⁻¹ (volumetric energy of 1.58 mWh cm⁻³) at a specific power of 1.875 kWh kg⁻¹ with 96.2% capacity retention over 10 000 charge–discharge cycles.