The viable mechanisms for O-3 generation via the electrocatalytic splitting of H2O over beta-PbO2 catalyst were identified through Density Functional Theory calculations. H2O adsorbed onto the surface was oxidized to form OH then O; the latter reacted with a surface bridging O to form O-2 which in turn reacted with another surface O to form O-3. The final step of the mechanisms occurs via an Eley-Rideal style interaction where surface O-2 desorbs and then attacks the surface bridging oxygen, forming O-3. A different reaction pathway via an O3H intermediate was found less favoured both thermodynamically and kinetically. (C) 2016 Elsevier B.V. All rights reserved.