Mechanism: Distributed Double-Layer Across The Cured Matrix

In an electric-double-layer capacitor, energy is stored by reversibly adsorbing ions from a liquid electrolyte onto an electronically conductive electrode surface. Capacitance scales linearly with accessible surface area, and energy stored scales with the square of the operating voltage. In a conventional packaged EDLC, the electrode is a porous activated-carbon film coated on a metal current collector, the electrolyte is an organic or aqueous solution sealed in a metal can, and the package volume is dominated by separator, casing, and dead space rather than by active material.

The cement-graphene composite distributes the electrode surface throughout the structural element. Biomass-derived graphene, dispersed at engineered loading into the cementitious mix prior to casting, forms a percolating conductive network through the cured matrix. The pore network of cured cement, naturally saturated with alkaline pore-water solution containing potassium, sodium, and calcium hydroxide species, provides the electrolyte. When voltage is applied between two electrically isolated regions of the element, ions in the pore water reorganize at the graphene-pore-water interface to form a Helmholtz double layer at every accessible graphene surface throughout the volume between the contacted regions.

Charge storage is therefore distributed in three dimensions across the cast element rather than concentrated at a packaged electrode-separator-electrode stack. The accessible surface area scales not with the footprint of a coated film but with the product of graphene-mass loading and the specific surface area of the graphene material. At biomass-derived graphene loadings of one to five percent by mass of binder, with specific surface areas in the range of three hundred to six hundred square meters per gram, a structural element of ordinary cubic-meter scale presents tens of thousands of square meters of double-layer interface.

The percolation threshold for the graphene phase determines the minimum loading at which a continuous electronic conduction path exists between the two current collectors; below this threshold the composite stores essentially no usable charge because the double-layer interfaces cannot equilibrate to the applied potential within practical time scales. Above the threshold, the conductive network develops rapidly, and accessible surface area approaches an asymptote set by the graphene-pore-water wetting condition. Pore-water saturation governs the ionic-conduction half of the charge-transport pathway; mature cured cement maintains a saturated pore network for the lifetime of the structural element except under sustained drying conditions, which the credentialed profile explicitly bounds through humidity and temperature monitoring at a sampling cadence proportional to the storage element's exposure regime.

Operating Parameters

Energy density of the cement-graphene EDLC scales with graphene loading, accessible surface area, and the square of the operating voltage window. The voltage window is bounded by the electrochemical stability of the alkaline pore-water electrolyte, which admits approximately 1.0 to 1.5 volts per cell before water electrolysis becomes the dominant Faradaic loss process. Within this window, the disclosed embodiments achieve 0.1 to 1 watt-hour per kilogram of structural material, modest by lithium-ion standards but sufficient to provide hours of building-load buffering when integrated across the full structural mass of a commercial building.

The graphene-loading parameter governs a trade-off between energy-storage admissibility and structural admissibility. Higher graphene loading raises capacitance and energy density, but at loadings above a threshold (typically five to seven percent by mass of binder, depending on graphene morphology and dispersion quality) the conductive phase begins to disrupt aggregate-binder bonding and reduce compressive strength. The credentialed profile expresses this trade-off explicitly: the structural admissibility surface bounds load-bearing capacity at the as-cast graphene loading, the energy-storage admissibility surface bounds dispatchable capacity at the same loading, and the mix design is selected to land both surfaces above operational thresholds simultaneously.

Calendar life is bounded by the structural element's design lifetime, typically fifty to two hundred years for cast cementitious structures, rather than by electrochemistry. The non-Faradaic storage mechanism contributes to this bound by avoiding the redox-driven degradation pathways that limit lithium-ion calendar life. Periodic re-credentialing, addressed in a separate disclosure, accommodates slow drift in graphene-network conductivity, pore-water-chemistry composition, and accessible surface area over decadal timescales.

Power density and round-trip efficiency follow from the equivalent series resistance of the distributed network, which is dominated at low loading by the graphene-graphene contact resistance and at high loading by the ionic resistance of the pore-water electrolyte through tortuous cement pores. Representative embodiments achieve discharge time constants on the order of seconds to tens of seconds for cubic-meter-scale elements, which is well matched to building-load buffering against short-duration grid disturbances and to dispatch against time-of-use tariff windows but is not matched to instantaneous power-quality applications requiring millisecond-scale response. Charge-discharge round-trip efficiency in representative embodiments falls in the range of seventy-five to ninety percent, with the bulk of loss attributable to ohmic dissipation in the percolating graphene network rather than to electrochemical irreversibility, and the loss budget is recorded in the credentialed profile alongside the energy and power surfaces.

Alternative Embodiments

The graphene phase admits multiple sources. The disclosed embodiments emphasize biomass-derived graphene produced from agricultural residues, woody biomass, and biochar precursors via flash Joule heating or controlled pyrolysis, which provides an order-of-magnitude cost advantage over chemical-vapor-deposited or chemically exfoliated graphene and admits carbon-negative life-cycle accounting when sourced from waste streams. Alternative embodiments include exfoliated graphene oxide subsequently reduced in situ, carbon nanotubes substituted for or co-loaded with graphene, and conductive carbon black at higher loading.

The cementitious binder admits multiple chemistries. Ordinary Portland cement is the reference embodiment; alternative embodiments include calcium-aluminate cement, magnesium-phosphate cement, alkali-activated geopolymer binders, and supplementary cementitious materials such as fly ash, slag, and silica fume blended at varying proportions. Each binder presents a distinct pore-water chemistry and therefore a distinct voltage window, capacitance, and self-discharge profile, and the credentialed profile records the as-cast composition for downstream dispatch and re-credentialing.

Electrode geometry within the cast element admits embodiments ranging from monolithic two-electrode cells (where two reinforcement cages serve as current collectors at opposite faces of a wall section) to multi-cell stacks cast as monolithic members with internal isolation layers. Series and parallel topologies are selectable at the design stage and recorded in the electrical-distribution surface of the profile. Internal isolation layers are realized through cast-in non-conductive cementitious laminae, polymer sheet inserts, or air-gap partitions, each selected against the structural and electrical-isolation requirements at the corresponding plane within the element, and each recorded in the as-built electrical-distribution surface of the credentialed profile alongside the corresponding inter-cell breakdown voltage and creepage-distance characterization.

Composition And Mix Design

A representative mix design for the cement-graphene composite comprises Portland cement binder at typical structural proportion, fine and coarse aggregate selected for the target structural class, water at a water-to-cement ratio appropriate to the structural admissibility surface, biomass-derived graphene at one to five percent by mass of binder, a polycarboxylate-ether superplasticizer to disperse the graphene phase and maintain workability, and a viscosity-modifying admixture to prevent graphene segregation during placement. Reinforcement is selected per the embodiment: steel rebar in conventional construction, carbon-fiber rebar in the cavity-bath variant where electrochemical isolation between reinforcement and the storage current path is required.

Current-collector contact is established at casting time through embedded conductive plates, mesh, or rebar terminations that emerge from the element's surface for external connection. The contact regions are designed against the electrical-distribution surface and recorded in the credentialed profile alongside the mix-design parameters, the as-cast graphene loading, and the post-cure characterization data (compressive strength, capacitance, equivalent series resistance, voltage window). Quality-assurance procedures at the casting plant or job site establish initial values for each surface and feed the credentialed profile its first admissibility envelope, against which subsequent re-credentialing events register their drift.

Prior-Art Distinction

Cement-based supercapacitors have appeared in the academic literature for over a decade, including reports of graphene-loaded mortar, carbon-fiber-loaded concrete, and carbon-black-cement composites operating as small-scale EDLCs. These prior-art disclosures typically (i) treat the storage function as a laboratory demonstration on centimeter-scale specimens rather than as a building-scale primitive cast at structural element dimensions, (ii) do not address the structural-lifetime calendar-life regime and instead report cycle-bounded figures consistent with conventional packaged supercapacitor expectations, and (iii) do not disclose a credentialed admissibility profile that admits trading off structural and storage surfaces against shared mix-design parameters within a unified dispatch and audit architecture.

The disclosed primitive's distinguishing elements are: the use of biomass-derived graphene at engineered loading to achieve cost-and-carbon-favorable scale; the explicit targeting of structural-relevant energy density (0.1 to 1 Wh/kg of structural material) rather than electrode-relevant figures; and integration with the credentialed admissibility profile that admits unified dispatch, re-credentialing, and end-of-storage-life attestation as architectural primitives rather than as ad-hoc supervisory features.

Disclosure Scope

The provisional disclosure encompasses the cement-graphene composite mix design, the biomass-derived graphene sourcing and engineered-loading parameter ranges, the pore-water-electrolyte voltage window, the embedded current-collector geometries, and the integration of structural and energy-storage admissibility surfaces within the credentialed profile. Independent claims address (i) a structural element comprising a cementitious binder, biomass-derived graphene at engineered loading, and current-collector geometry sufficient to admit EDLC operation at structural-relevant energy density without compromising compressive strength, and (ii) the corresponding mix-design and casting method. Dependent claims address binder alternatives, graphene-source alternatives, loading ranges, voltage-window operation, and credentialed-profile integration including series-stack topology recording in the electrical-distribution surface.

The disclosure further contemplates that the cement-graphene EDLC may be deployed in non-building infrastructure contexts including pavement sections, bridge decks, retaining walls, and underground vault structures, in each case integrating the storage surface with whatever electrical-distribution infrastructure is available at the site. Where the host structure carries dynamic mechanical loads (vehicular traffic, hydrostatic pressure variation, thermal cycling), the credentialed profile additionally records the fatigue-loading regime and admits a cycle-count-aware structural admissibility surface that interacts with the storage surface only through the shared mix-design parameters rather than through any direct electrochemical coupling.