diffusion current (diffusion-controlled current)

https://doi.org/10.1351/goldbook.D01722
A
faradaic current
whose magnitude is controlled by the rate at which a reactant in an electrochemical process diffuses toward an electrode-solution
interface
(and, sometimes, by the rate at which a product diffuses away from that
interface
). For the
reaction mechanism
there are two common situations in which a
diffusion
current can be observed. In one, the rate of formation of B from electroinactive C is small and the current is governed by the rate of
diffusion
of B toward the electrode surface. In the other, C predominates at equilibrium in the bulk of the solution, but its
transformation
into B is fast; C diffuses to the vicinity of the electrode surface and is there rapidly converted into B, which is reduced.
Source:
PAC, 1985, 57, 1491. (Recommended terms, symbols, and definitions for electroanalytical chemistry (Recommendations 1985)) on page 1495 [Terms] [Paper]