Recently, structural supercapacitors have attracted considerable attention due to their concurrent capability to store electrochemical energy and support mechanical loads. However, the greatest challenge in realizing an integrated electro-mechanical system is the development of highly compatible electrodes and structural electrolytes with superior mechanical and electrochemical performance. Here, a structural supercapacitor assembled with a 3D rGO@MnO₂ nickel foam electrode and polyacrylic acid–Portland cement–KOH electrolyte is reported to solve the challenge for the first time. The resulting rGO@MnO₂ electrode exhibits a high areal capacitance of 1.84 F cm⁻² at 0.5 mA cm⁻², with the areal capacitance remaining at 1.13 F cm⁻² even at a current density of 40 mA cm⁻². The structural electrolyte with 6 wt% polyacrylic acid–Portland cement–KOH shows the best combination of an ionic conductivity of 2.13 mS cm⁻¹ and a compressive strength of 28.5 MPa. The resulting asymmetric structural supercapacitor with an areal capacitance of 51.5 mF cm⁻² at 0.1 mA cm⁻² is superior to those reported in latest studies based on carbon materials and resin, which suggests its potential application in structural energy storage for civil engineering.

Multifunctional structural supercapacitor based on the structural electrolyte of cement/PVA-KOH composite and the structural electrode of highly electrically graphene was fabricated with sandwich structure. A bicontinuous microstructure composed of PVA and hardened cement paste is formed. Flexible PVA in cement/PVA-KOH composite increases ions’ accessibility with graphene at the interface between the structural electrode and the structural electrolyte. The addition of KOH changes the structure of PVA from crystalline state to amorphous state. So PVA can complex and discomplex with KOH to realize ionic conduction. The effects of PVA’s content, polymerization degree and hydrolysis degree on the electrochemical properties and mechanical properties were analyzed. The composite’s ionic conductivity increases with PVA’s content and hydrolysis degree, and it shows a tendency of decreasing after increasing with PVA’s polymerization degree. Similarly, the specific capacitance of the structural supercapacitor also increases with PVA’s content and hydrolysis degree, but decreases with PVA’s polymerization degree. Compared with the polymerization degree, the hydrolysis degree plays a more prominent part in affecting the specific capacitance of the structural supercapacitors. For mechanical properties of cement/PVA-KOH composite, the compressive strength is mostly improved by PVA at a content of 2%. It decreases with PVA’s polymerization degree and increases with PVA’s hydrolysis degree. The conflict between the power density and energy density in structural energy storage is eased remarkably and the electrical and mechanical properties can be improved simultaneously. The two chief obstacles are tackled in the PVA1799-based structural supercapacitor.