The catalyst development process is based on so called rational design in which one synthesizes only materials showing prospective activity in theoretical and computational prescreening. This prescreening can be done by computational assessment of the binding energies of OER surface intermediates on candidate surfaces. Such analysis allows for determination of the potential limiting reaction step, and thereby the theoretical overpotential . The method is however crucially dependent on the reaction mechanism embedded into the calculation. Reaction mechanism modelling is therefore a central part of the computational approach.