Electrochemistry Dictionary - U

Ultracapacitor: See electrochemical capacitor.
Ultramicroelectrode: A very small electrode, with dimensions not larger than few tens of a micrometer, and occasionally with dimensions of a fraction of a micrometer.
Uncompensated IR drop: The part of the solution IR drop that is not automatically compensated for by the electronic control instrumentation.
Uncompensated (solution) resistance: See uncompensated ir drop.
Underpotential deposition: The electrodeposition of a metal on a foreign metal at potentials less negative than the equilibrium potential of the deposition reaction. Such a process is energetically unfavorable and it can occur only because of a strong interaction between the two metals, with their interaction energy changing the overall energetics to favorable. Consequently, only one (very seldom two) monolayer can be deposited this way, and this is a very convenient way to produce well-controlled monolayer deposits. Abbreviated as "UPD."
Uninterruptible power supply (UPS): A power system which maintains current flow without even a momentary break, in the event of mains or generator failure.
Unpolarizable electrode: See non-polarizable electrode.
UPD: Stands for underpotential deposition.