This phenomenon was originally understood through Michael Faraday's work and expressed in his laws of electrolysis.
[1] Faradaic losses are experienced by both electrolytic and galvanic cells when electrons or ions participate in unwanted side reactions.
[2] The fraction of electrons so diverted represent a faradaic loss and vary in different apparatus.
Failure to account for this Faraday-efficiency effect has been identified as the cause of the misidentification of positive results in cold fusion experiments.
Another is overpotential, the difference between the theoretical and actual electrode voltages needed to drive the reaction at the desired rate.