Activated carbon microtube electrodes with cement and fly ash for enhanced supercapacitor performance

Abstract

We developed chemically activated carbon microtubes (ACMTs) from waste surgical face masks and combined them with fly ash (FA) and cement (CE) to create symmetric electrodes for high-performance supercapacitors. The facemasks were carbonized at 700 °C and then activated with KOH at 900 °C to produce ACMTs with hierarchical porosity and tubular structure, as confirmed by SEM and HR-TEM analyses. Raman spectroscopy showed a higher defect density in ACMTs (I_D/I_G = 1.30) compared to pristine carbon microtubes (CMTs; I_D/I_G = 1.19), while BET analysis indicated an improved surface area of 1310 m² g⁻¹. The unique combination of FA and CE is vital for electrode performance, FA acts as a conductive additive, aiding charge transport through its metal oxide content, while CE functions as a stable binder, enhancing structural integrity and ion diffusion pathways. The optimized ACMT₂/FA₁/CE₁ electrode delivers a high specific capacitance of 669 F g⁻¹ at 1.0 A g⁻¹ in 3 M KOH. The corresponding solid-state symmetric device (NF/ACMT₂/FA₁/CE₁) retains 94.2% of its capacitance after 10 000 cycles and achieves an energy density of 87 Wh kg⁻¹ at 750.5 W kg⁻¹. Expanding the potential window with an alkaline electrolyte further boosts the energy density, demonstrating that ACMT-based, waste-derived electrodes provide a sustainable and low-cost pathway towards high-performance supercapacitors.