For O 2 reduction on LaFeO 3 , the gradient ∂∆χ( ⃗ E)/∂η act ( ⃗ E) = -0.86, while the linear fit to the experimental data ∂∆χ/∂η act = -0.47 (Fig. ). The general trend is captured correctly, however, the model overestimates the shift in electrostatic surface potential. The most obvious reason for the error observed in Fig. is the simplicity of the model, where strontium was not included in the DFT calculation. We chose to use Fe on the surface layer as it was reported to be the most stable termination under operational conditions. However, we found that using strontium or lanthanum in the terminating layer had a negligible effect on the dipole moment of the surface. Additionally, doping strontium into the subsurface layer also had a negligible effect on the dipole moment of the surface. Guan found inconsistencies in the ∂∆χ/∂η act relationship with respect to variations in the La:Sr ratios. Guan also observed that the ∂∆χ/∂η act relationship was dependent on the p O 2 of the environment.