This paper considers the control of the concentration of a reactant on the reactive surface of an electrode in an electrochemical system, where the reactant mass transfer to the electrode is limited by diffusion. The aim is to maximize the reaction rate at the surface still avoiding total depletion of the reactant at the electrode. It is shown that this boundary control problem of the said physically distributed system can be solved relatively simply by using a modified linear quadratic Gaussian regulator. First the finite diffusion process with mixed boundary conditions is solved analytically and approximated with a discrete-time system which is formulated as a function of the current control action and the cumulative past controls actions. Several simulations accompany the discussion and a stochastic approach is utilized, which enables the controls to compensate for model inadequacies and measurement inaccuracy and thereby makes the presented approach better applicable in practice. (C) 2011 Elsevier Ltd. All rights reserved.