We note that this relationship between CO2R activity and Ni loading is different between NiPACN and NiPACN. As reported in our earlier publication, NiPACN shows an increase in jCO (at a given electrode potential) with increasing Ni loading up to ~2 wt% Ni after which the jCO plateaus. In contrast, the 61 NiPACN samples do not seem to have a plateau in jCO and instead a decline in CO2R activity is observed at the highest loading. We hypothesize that this difference arises from the different synthetic methods used for the catalysts. In particular, the This morphology is characteristic of this synthesis that uses polyacrylonitrile particles as the carbon-precursor and the samples show no obvious differences as a function of Ni loading. No other features are present for the 0.1 wt% and 0.5 wt% samples but the 1 wt% samples have metallic Ni peaks at 44.5 o and 52 o . In addition, the graphitic features on all three samples became monotonically sharper with increased Ni loading in agreement with prior findings. As metallic Ni is a catalyst for graphitization, this suggests that the metallic Ni content of the samples also increases with Ni loading though the amount of metallic Ni in the 0.5 wt% sample is below the detection limit of PXRD. These PXRD results are consistent with the monotonic increase of HER with loading and suggest that dispersed sites are dominant in the 0.1 wt% and 0.5 wt% samples while Ni aggregates dominate the 1 wt% sample. X-ray photoelectron spectroscopy (XPS) provides additional information on the chemical states of the N and Ni dopants in 61 NiPACN (SI-Figure ). The N1s region of all samples can be deconvoluted into characteristic peaks at 398.2 eV, 401.1 eV, and 403.6 eV, corresponding to pyridinic, graphitic, and oxidized N respectively. The fraction of N into these three categories of N defects does not substantially change between the samples (SI-Table ) which is consistent with very small amounts of Ni incorporation that doesn't substantially affect the signal from the relatively large XPS probe depth compared to the surface defects. The Ni 2p region shows only very weak signal for the 0.1 wt% sample due to the Ni content being below the typical detectability limit of XPS. The 0.5 wt% sample shows a clear peak at 854.6 eV, corresponding to Ni 2+ , which is consistent with the oxidation state of NiNx states reported in prior publications. The 1 wt% sample has a small feature at the same energy, ~855 eV, corresponding to Ni 2+ , which conflicts with the existence of Ni nanoparticles and higher Ni content implied by the preceding analysis.