To explore the near-surface site density-normalized, intrinsic catalytic CO2 reduction kinetics of the single Ni atom catalysts and contrast their respective site accessibility, partial CO current densities and CO turn over frequencies were derived for different catalyst loadings. This was carried out in a conventional liquid-electrolyte H-type cell and compared to a number of benchmark NiNC-catalysts (Supplementary Figure ). Our two NiNC electrocatalysts in focus showed a peak 85-90% CO faradaic efficiency (FECO) at approximately -0.75 VRHE (Supplementary Figure ). The NiNC-IMI displayed the highest CO mass activity (exceeding 25 mA mg -1 ), thanks to its high active site density related to its mesoporous structure (Supplementary Figure ), closely followed by NiNC-PANI. Normalization of the mass (or equally geometric area) activity data using the Ni-Nx surface site density, almost identical intrinsic TOF vs E relations ensued. This suggests the presence of similar active Ni-Nx motifs in the various NiNC catalysts (Supplementary Figure ), which is surprising given the vastly different chemical nature of the synthetic pathways. Yet, it underscores the insensitivity of the emerging active site during pyrolysis to the chemical nature of the precursors. Supplementary Figure also reveals vastly different TOF-E trajectories for E < -0.75 V. This difference is not due to varying site densities, but due to varying site accessibility. Mesoporous catalysts (NiNC-IMI) offer enhanced site accessibility and suffer from local CO2 depletion resulting in plateauing TOF-E relations. For a more in-depth analysis of the NiNC catalysts, different geometric loadings were tested (Figure -g, Supplementary Figure ) and the results