This article presents a mathematical model that predicts the chemical conditions at the electrode surface during the electrochemical reduction of CO2. Such electrochemical reduction of CO2 to valuable products is an area of interest for the purpose of reducing green house gas emissions. In the reactions involved, CO2 acts as both a reactant and a buffer, consequently the estimation of local concentrations at the electrode surface is not trivial and a numerical approach is required. The necessary partial differential equations (PDEs) have been set-up and solved using MATLAB. The results show the local concentrations at the electrode surface to be significantly different from the bulk concentrations under typical reported experimental conditions. The importance of buffer strength and a careful quantification of the degree of mixing produced in the experimental apparatus is demonstrated. The model has also been used to re-examine previously published data, showing that the Tafel slopes in CO2 reduction are consistent with those reported for the simpler CO reduction system. Further, the effect of pulsed electroreduction was also modeled, showing that pulsing causes corresponding swings in local pH and CO2 concentrations.