By contrast, NiNC-PANI provides a much higher surface area of 414 m 2 g -1 , due to the dominant microporosity (Supplementary Figure ). These distinct powder characteristics will, as shown below, translate into characteristic differences in their cathode layers and, consequently, in the respective electrolyzer cell performances, reflected in their carbon crossover diagnosis introduced below. By combining the BET-surface area and the XPS nearsurface fraction of Ni 1+/2+ species related to Ni-Nx motifs, we estimated and compared the Ni-Nx surface site density (SD) to other NiNC catalysts (Supplementary Note 2, Supplementary Figure ). NiNC-PANI and NiNC-IMI catalysts showed the highest exposed SD of all considered benchmark catalysts.