A theory is presented for the shape of current curves measured at a rotating-disc electrode for the cases where the substrate reacts via for the E, EC' and ECE reaction mechanisms respectively. An analytical expression of concentration and current is presented by solving convection-diffusion equations for the E and EC' reaction mechanism. The closed-form of an analytical expression of concentration and current for ECE reaction mechanisms are also reported by solving the system of nonlinear reaction-convection-diffusion equations using homotopy-perturbation method. The solutions enable us to obtain the current response in chronoamperometry and steady-state voltammetry. Analytical results are also compared with the simulation result. An excellent agreement is observed between the series of solutions obtained by simulation solution. The approximate analytical expression derived here is useful to predict the dynamical behaviour of the system. The effect of the parameters on concentration and current are discussed and presented graphically. (C) 2019 Elsevier Ltd. All rights reserved.