Optimizing fly ash and H2O2 content for sulfoaluminate cement-based supercapacitors: Balancing capacitance and exceptional cycling stability

To meet the integrated development demands of building structures and energy storage systems, cement-based supercapacitors (CBS) have emerged as promising low-carbon functional construction materials because of their dual load-bearing and energy-storage capabilities. However, their practical application is still limited by poor electromechanical coupling efficiency, insufficient cycling stability, and the high carbon emissions of cementitious matrices. In this study, CBS were fabricated using sulfoaluminate cement as the matrix, fly ash (FA) as an active stabilizer, acetylene carbon black (ACB) as the conductive filler, and H 2 O 2 as a chemical foaming agent. The ACB content was first optimized to construct a robust conductive network, and the synergistic mechanism of FA (0–50 wt%) and H 2 O 2 in regulating pore structure, mechanical integrity, and electrochemical durability was systematically investigated. The optimized CBS with 7 wt% ACB and 50 wt% FA achieved a compressive strength of 20.51 MPa, an areal capacitance of 728.12 mF/cm 2 (at 1 mA/cm 2 ), an energy density of 101.13 μWh/cm 2 , and a power density of 1.56 mW/cm 2 . Although the optimized 50 wt% FA group exhibited 13.5% and 9.4% lower initial capacitance than the FA-free control (F0) and the H 2 O 2 -free control (F50–1), respectively, it retained 96.23% of its capacitance after 5000 cycles with nearly 100% Coulombic efficiency; in contrast, the H 2 O 2 -free and FA-free controls retained only 63.66% and 71.85% after 1000 cycles, respectively. Mechanistically, FA micro-aggregate filling and the pozzolanic reaction consumed Ca(OH) 2 and generated secondary C–S–H gel, which refined the pore structure, densified the interfacial transition zone, stabilized the conductive network, and suppressed microcracking under repeated ion insertion/extraction. A 3-parallel-3-series device powered an LED for 128 s, confirming effective voltage and capacity scaling. This work elucidates the FA/H 2 O 2 synergistic mechanism for enhancing CBS durability and provides a technical pathway for the high-value, low-carbon utilization of FA in multifunctional construction materials.