Composition-dependent charge-storage kinetics and heterojunction charge-transfer dynamics in $$\:{\text{WO}}_{3}/{\text{g-C}}_{3}{\text{N}}_{4}/{\text{BiVO}}_{4}$$ nanocomposites

Optimizing electrode materials for supercapacitors requires a precise balance between electronic conductivity and rapid ion-diffusion kinetics. In this work, a ternary \(\:{\text{WO}}_{3}/{\text{g-C}}_{3}{\text{N}}_{4}/{\text{BiVO}}_{4}\) heterostructure nanocomposite was synthesized via hydrothermal and sonication-assisted routes to investigate composition-dependent charge-storage kinetics and interfacial charge-transfer dynamics. Structural (XRD), morphological (SEM/EDX), and chemical (XPS) analyses confirmed multi-phase heterojunction formation, high elemental purity, and intrinsic microstrain ( \(\:\epsilon\:=0.0136\) ). UV–vis diffuse reflectance spectroscopy (DRS) demonstrated enhanced visible-light response with a narrowed bandgap ( \(\:{E}_{g}=2.14\text{\:eV}\) ), indicating improved electronic coupling across phase boundaries. Electrochemical evaluations in a three-electrode setup ( \(\:3\text{\:M\:KOH}\) ) revealed that while the binary \(\:{\text{WO}}_{3}/{\text{g-C}}_{3}{\text{N}}_{4}\) matrix provides high surface-controlled capacity ( \(\:26.85{\text{\:mAh\:g}}^{-1}\) at \(\:2{\text{\:A\:g}}^{-1}\) ), incorporation of \(\:{\text{BiVO}}_{4}\) modulates the underlying charge-storage mechanism. Power-law kinetic fitting ( \(\:b=0.4071\) ) and low-frequency Warburg impedance analysis confirm that charge storage in the ternary composite ( \(\:{Q}_{s}=4.32{\text{\:mAh\:g}}^{-1}\) at \(\:2{\text{\:A\:g}}^{-1}\) ) is governed by semi-infinite bulk diffusion rather than rapid surface pseudocapacitance. EIS analysis demonstrated a significant reduction in charge-transfer resistance ( \(\:{R}_{ct}\approx\:80\:{\Omega\:}\) ) compared to pristine \(\:{\text{BiVO}}_{4}\) ( \(\:\sim\:450\:{\Omega\:}\) ), while long-term GCD testing showed stable cycling with \(\:\sim\:75\text{-}76\%\) capacity retention after 5000 cycles and high Coulombic efficiency ( \(\:\sim\:98.5\%\) ). This study clarifies that \(\:{\text{BiVO}}_{4}\) incorporation acts as a kinetic tuner modulating interfacial mass-transport dynamics rather than a total capacity booster, offering critical insights for engineering multi-phase metal oxide heterostructures.