Electrolyte-driven modulation of charge storage mechanisms in Co metal–organic frameworks for advanced supercapacitors

Abstract

This study examines the influence of electrolytes and the molarity-dependent electrochemical evaluation of Co-MOF-based electrodes for supercapacitor applications. The synthesized Co-MOF was analyzed using XRD, FTIR and FE-SEM techniques, which collectively confirmed the successful formation of the material. The electrochemical performance was evaluated using CV, GCD and EIS in alkaline electrolytes of different molarities. Co-MOF exhibited a C_sp of 379.31 F g⁻¹ and 852.5 F g⁻¹ in KOH and NaOH, respectively, at a scan rate of 2 mV s⁻¹, indicating superior response in NaOH. Similarly, GCD measurements revealed an enhanced C_sp of 1147.2 F g⁻¹ at 0.5 A g⁻¹ in NaOH, compared with 317.86 F g⁻¹ in KOH. The molarity of the electrolyte was varied (1 M NaOH, 3 M NaOH and 5 M NaOH), and 1 M NaOH displayed optimal performance, while maintaining a ∼98% of the capacitance retention after 10 000 cycles. A symmetric Co-MOF Swagelok supercapacitor utilizing 1 M NaOH showed a C_sp of 37.7 F g⁻¹ (CV) and 14.9 F g⁻¹ (GCD) at 0.25 A g⁻¹ with a maximum E_d of 3.73 W h kg⁻¹ at a P_d of 118.75 W kg⁻¹ and ∼43.96% retention after 10 000 cycles. Similarly, at a scan rate of 2 mV s⁻¹, the Co-MOF pouch cell exhibited a C_sp value of 21.42 F g⁻¹ from CV and a peak capacitance of 1.68 F g⁻¹ when evaluated at 0.25 A g⁻¹ for GCD. Ragone analysis revealed that the device delivered an E_d of 0.22 W h kg⁻¹ at a corresponding P_d measured at 43.75 W kg⁻¹. The results underscore the importance of concentration and electrolyte selection as critical parameters for Co-MOF supercapacitor performance.