AQUEOUS ELECTROLYTES

Water-based: cheap, fast, forgiving

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Acidic

H₂SO₄ solution. Very conductive, and common with carbon electrodes

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Alkaline

KOH solution. Very conductive, and suited to many oxide electrodes

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Neutral

Salts such as Na₂SO₄ or KCl. Milder and safer, with a wider window

Water dissolves salts well, needs no dry room, and doesn't burn.

WHY WATER IS FAST

Small ions, high conductivity

Conductivity Acids and bases often reach 0.4 S/cm or more, roughly ten times typical organic electrolytes

Protons hop H⁺ moves by passing between water molecules, which makes acids especially quick

Handling Assembled in ordinary air, with low cost and low fire risk

The catch Strong acids and bases attack many metal current collectors and seals

Low resistance and low cost make aqueous cells the workhorse of the lab.

THE 1.23 V CEILING

Water splits, and that caps the voltage

2 H₂O → 2 H₂ + O₂

Thermodynamically, water splits into hydrogen and oxygen at about 1.23 V. Acidic and alkaline carbon cells usually run near 1 V. Neutral salt solutions can reach roughly 1.6 to 2 V, because gas evolution is slow on carbon and delays the splitting.

A 2.7 V organic cell holds about (2.7 / 1.0)² ≈ 7 times the energy of a 1 V cell with the same capacitance.

WATER-IN-SALT

Starving water of its freedom

salt ≫ water

In a water-in-salt electrolyte, so much salt is dissolved (around 20 moles per kilogram of water for some lithium salts) that nearly every water molecule is tied up around an ion. With little free water left to split, the window can stretch to roughly 2.5 to 3 V while staying non-flammable.

The catches: expensive salts and higher viscosity, so it trades some cost and speed for voltage.

UNIT 21 STUDY COMPLETE

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Ready for the Fab Challenge?

You've covered acidic, alkaline, and neutral water-based electrolytes, and the 1.23 V ceiling.