Spatial Sites Separation Strategy to Fabricate Atomically Isolated Nickel Catalysts for Efficient CO₂ Electroreduction

Fabrication of highly active carbon-supported atomically isolated metal catalysts with maximized atomic efficiency is significant but remains a big challenge because the adjacent metal species are easy to be aggregated during pyrolysis. Herein, a spatial sites separation strategy is developed to fabricate fully atomically isolated nickel catalysts for highly efficient CO2 electroreduction reaction (CO2RR). The porous porphyrinic triazine frameworks (designated as PTF-Zn, PTF-ZnNix, and PTF-Ni100, x = 5, 20, refers to molar percentage of Ni-TPPCN monomer) were first obtained by the polymerization of the monomers 5,10,15,20-tetrakis(4-cyanophenyl)porphyrin (TPPCN) or [5,10,15,20-tetrakis(4-cyanophenyl)porphyrinato]-Ni (Ni-TPPCN) with different molar ratios in the presence of ZnCl2. The distances between the Ni-N4 units that spatially separated by in situ formed Zn-N4 units in these PTF frameworks can be controlled by tuning the ratio of the monomers of Ni-TPPCN and TPPCN. Thus, because of the successful implementation of spatial sites separation strategy, pyrolysis of PTF-ZnNi5 that the Ni-N4 units were separated by Zn-N4 moieties afforded Ni5-PFT-1000 with fully atomically isolated Ni active sites. In contrast, pyrolysis of PTF-ZnNi20 or PTF-Ni100 led to porous carbon catalysts containing nickel nanoparticles (Ni NPs) because of the very limited spatial separation of Ni-N4 units with or without Zn-N4, allowing Ni migration and aggregation to occur. Consequently, porous Ni5-PTF-1000 was highly active for CO2RR toward CO with a high Faradaic efficiency (FE) of 94% at −0.9 V, larger CO partial current density of 18.4 mA cm–2, high turnover frequency value (TOF) of 20180 h–1 at −1.0 V. In contrast, Ni20-PFT-1000 and Ni100-PFT-1000 containing Ni NPs had lower FE of 79.7% and 6.8%, respectively, for the conversion of CO2-to-CO at the same potential. This work presents a facile way to achieve highly active catalyst with fully atomically dispersed sites for CO2RR catalysis.