Identification of all possible kernel functions associated with integral equation-based simulations of transient experiments for (pseudo-)first order homogeneous reaction-diffusion systems is an unsolved problem. Convolution concentration-flux relationships are derived for the catalytic EC' reaction mechanism at spherical electrodes, assuming unequal diffusion coefficients of the members of the redox couple (D-O not equal D-R). The relationships involve new kernel terms, thus far unknown to be of importance to the theory of electroanalytical experiments. The new kernels are incorporated into the adaptive Huber method for solving integral equations that describe the experiments. The resulting algorithm is used to simulate chronoamperometry and cyclic voltammetry. It is found that the effect of D-O not equal D-R can be considerable. Integral equations obtained for D-O not equal D-R appear more difficult to solve numerically than the integral equation arising for D-O = D-R. (c) 2019 Elsevier Ltd. All rights reserved.