Polarisation curve

Example

Use in Lemonergy

Connect reaction sites and transport paths.

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Connected concepts

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Concentration polarization

Voltage loss that arises when reactant is consumed faster than diffusion can replace it, so the concentration at the surface differs from the bulk. It dominates at high current and low temperature and recovers slowly when current stops.

Fuel cell

An electrochemical converter that makes electricity from a fuel, usually hydrogen, and oxygen as long as both are supplied, rather than storing energy in its electrodes. Fuel-cell vehicles still carry a battery to buffer power.

Open-circuit voltage

The voltage across a cell’s terminals when no current flows and the cell has rested long enough for the voltage to settle. It depends on state of charge and temperature, and a cell whose open-circuit voltage falls unusually fast in storage may have an internal short.

Overpotential

The extra voltage, beyond the equilibrium potential, needed to drive a reaction at a given rate at one electrode. Activation overpotential pays for charge transfer, concentration overpotential for depleted reactant, and both appear as polarization at the terminals.

Polarization

The gap between a cell’s terminal voltage under load and its open-circuit voltage. It has ohmic, charge-transfer and concentration parts, grows with current and falling temperature, and is where delivered energy is lost.

Pulse test

Applying a current step of defined size and duration and recording the voltage response. The instant voltage step gives the ohmic resistance, the following curve the slower polarization; HPPC is a standardised sequence of such pulses across state of charge.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. Quantities, Units and Symbols in Physical Chemistry, 3rd edition, 2nd printing

   IUPAC · 2011

   Topic background · Physical-chemistry notation, thermodynamics, electrochemistry and transport quantities.