Electrolyte-engineering for enhanced charge storage in Ni metal–organic framework electrodes for high performance supercapacitors

Abstract

The work explores the effects of electrolyte composition and concentration on the electrochemical performance of Ni-MOF electrodes for supercapacitor applications. The synthesized Ni-MOF was structurally and morphologically characterized by XRD, FE-SEM, and XPS. The electrochemical properties were systematically evaluated through CV, GCD, and EIS in alkaline electrolytes of different compositions. Initial investigations were performed in 1 M KOH and 1 M NaOH to assess the effect of electrolyte selection. The Ni-MOF electrode showed a higher electrochemical response in NaOH than in KOH, indicating improved ionic transport and greater utilization of active sites in NaOH. Accordingly, studies were conducted by varying the NaOH concentration (1 M, 3 M, and 5 M). Among these, the 1 M NaOH electrolyte exhibited the max. C_s obtained from CV analysis of 986.6 F g⁻¹, while GCD measurements delivered a C_s of 433.23 F g⁻¹, confirming the enhanced charge storage capability in NaOH electrolyte. To evaluate practical applicability, a Symmetric SC device was constructed using Ni-MOF electrodes in a Swagelok cell with 1 M NaOH electrolyte. The device delivered a C_s of 31.76 F g⁻¹, and 8.75 F g⁻¹ from CV and GCD, respectively, with an E_d of 1.75 Wh kg⁻¹ at a P_d of 85 W kg⁻¹ and good cycling stability over 2000 cycles. In addition, a flexible Ni-MOF pouch cell device was fabricated and tested, which exhibited a C_s of 36.6 F g⁻¹ (CV) and 3.24 F g⁻¹ (GCD). Ragone plot analysis indicated an E_d of 0.729 Wh kg⁻¹ at a P_d of 33.75 W kg⁻¹. Overall, the results highlight that careful selection and optimization of electrolyte concentration are important for improving the electrochemical behaviour of Ni-MOF-derived supercapacitors.