Carbon-regulated ZnS heterostructures for pseudocapacitors: unveiling the suppressive effect of excess carbon on specific capacitance and electrochemical kinetics

A ZnS–carbon heterostructured electrode was synthesized using different initial carbon loadings and systematically investigated for pseudocapacitive energy storage. The study focuses on elucidating how carbon loading influences the structural, interfacial, and electrochemical characteristics of the resulting ZnS–carbon heterostructures. Structural and morphological analyses confirmed the formation of crystalline ZnS associated with the carbon framework, while XPS analysis further verified the surface coexistence of Zn, S, and C in the optimized CZS1 sample. Electrochemical evaluation revealed a mixed charge-storage mechanism involving ZnS-associated Faradaic reactions and surface-controlled contributions. Among the investigated compositions, CZS1 exhibited the highest specific capacitance, reaching 30.6 F g −1 from GCD at 0.3 A g −1 and 27.4 F g −1 from CV at 10 mV s −1 , together with 93.5% capacitance retention after 3000 cycles. Kinetic analysis indicated predominantly diffusion-influenced charge storage, while impedance analysis showed comparatively lower interfacial charge-transfer resistance for CZS1 than for the higher‑carbon-loaded compositions. Increasing the initial carbon loading resulted in a progressive decrease in specific capacitance and, particularly for CZS3, a marked increase in charge-transfer resistance, indicating reduced utilization of ZnS-associated electroactive sites. Overall, the results demonstrate that increasing carbon loading does not necessarily enhance electrochemical performance and that an appropriate ZnS–carbon balance is important for effective charge storage. The work highlights the carbon-loading-dependent structure–property relationship and the suppressive effect of excessive carbon incorporation on ZnS-associated pseudocapacitive activity, providing useful guidance for compositional optimization of ZnS–carbon electrodes.