THE INTERFACE

Electrode meets electrolyte

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Conventional capacitor

Stores energy across a solid dielectric layer between two plates.

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Supercapacitor

Stores energy at the interface between an electrode and an electrolyte.

That interface can hold capacitance several orders of magnitude greater than a conventional capacitor.

SURFACE VS. BULK

Not a battery

Battery Energy stored by diffusion-controlled chemical reactions throughout the bulk of the electrode

Supercapacitor Energy stored by surface-based processes at the electrode-electrolyte interface

Surface processes are fast and gentle on the material — that's why supercapacitors charge quickly and last so many cycles.

CHARGING, STEP BY STEP

Electrons out, ions in

During charging, an external circuit supplies electrons to one electrode and removes them from the other. Ions in the electrolyte then migrate toward the oppositely charged electrode surfaces to keep everything electrically neutral. The resulting charge separation is the stored energy.

e⁻ → electrode | ions → surface

Discharging simply runs the process in reverse, releasing that stored energy to a load.

THREE CATEGORIES

Sorted by mechanism

EDLC

Electrostatic ion accumulation at the interface

Pseudocapacitor

Fast, reversible faradaic redox reactions at the surface

Hybrid

Combines both mechanisms in a single device

EDLCs tend to win on power and cycle life; pseudocapacitors tend to win on capacitance and energy density.

UNIT 5 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered EDLCs, pseudocapacitors, and hybrids — and how surface storage differs from a battery.