Effect mechanisms of activators on the electrolyte performance of solid waste structural supercapacitors

Utilizing steel slag and granulated blast furnace slag, this study prepared solid waste electrolyte (SWE) for green building components integrating load-bearing and energy storage functions. However, simultaneously achieving high ionic conductivity and compressive strength remains challenging. Salt activators (4% Na/K₂SiO₃, Na/K₂SO₄), alkali activators (4% Na/KOH), and combined activators (2% + 2%) were employed to clarify activator effects on performance. Ionic conductivity and compressive strength were measured, and microstructures were characterized by thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry. Results showed that activators significantly improved SWE performance. The combined activators 2% K₂SO₄ + 2% KOH exhibited optimal overall performance (19.89 mS·cm⁻¹ and 16.15 MPa). K activation exhibited higher ionic conductivity than Na activation, whereas salt activation showed greater strength than alkali activation. Microstructural analysis indicated that activators promoted hydration, reduced porosity, and optimized pore size distribution. A synergistic influence was identified: porosity determines ion-accessible volume and microstructural compactness, whereas pore size distribution reflects the size and efficiency of ion-transport pathways and microstructural uniformity. Specifically, pores of 50–200 nm mainly contribute to ion transport, while pores > 200 nm mainly affect strength. Thus, reducing porosity and optimizing pore size distribution are crucial for simultaneously improving conductivity and strength of SWE.