Introducing mesoporous silica-protected calcination for improving the electrochemical performance of Cu@Fe–N–C composites in oxygen reduction reactions and supercapacitor applications

Abstract

The application of zeolite imidazolate framework (ZIF)-based nanomaterials for oxygen reduction reaction (ORRs) and supercapacitors (SCs) is drastically confined by their quick aggregation and irreversible fusion of metal nanoparticles. Herein, the impact of using the mesoporous silica-protected calcination strategy on the CuFe-ZIF composite is studied. To this end, the CuFe-ZIF catalyst was first prepared and then covered by mesoporous silica (mSiO₂). The acquired CuFe-ZIF@mSiO₂ was pyrolyzed at 900 °C under an Ar atmosphere. After pyrolysis and acid etching, the Cu@Fe–N–C nanomaterial was formed. The synthesized samples were evaluated by physical and electrochemical tests. According to the results, Cu@Fe–N–C with mSiO₂ protection exhibited better ORR catalytic activity with an onset potential of −0.04 V vs. Ag/AgCl compared to the unprotected sample (−0.17 V vs. Ag/AgCl). Besides, its average electron transfer number was found to be 3.55, indicating a 4-electron pathway for ORR. Furthermore, it offered excellent performance in a supercapacitor by applying the mSiO₂ cover, and the specific capacitance value significantly enhanced from 191 F g⁻¹ to 341 F g⁻¹ at a current density of 1 A g⁻¹. Therefore, it can be deduced that by employing the mesoporous silica covers during calcination process, the electrochemical properties of CuFe-ZIF-based materials can be considerably improved.