Electrochemical CO2 Reduction (CO2R) can potentially allow for the sustainable production of valuable fuels and chemicals. Recently, single atom catalysts on a 2D support have been shown to be a promising catalyst candidate. Using state-of-the-art methods, we develop a model for Fe doped graphene which rationalises several critical experimental observations: the contentious origin of the pH dependence of reactivity and the dependence of current-potential relationships on active site. We show that single atom catalysts have the unique ability to stabilise different dipoles associated with critical reaction intermediates, which translates to significant shifts in activity. This provides a new rational design principle and paves the way for rigorous computation-guided catalyst design of new single atom catalysts for CO2R.