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-Ni-100, 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-N-4 units that spatially separated by in situ formed Zn-N-4 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-N-4 units were separated by Zn-N-4 moieties afforded Ni-5-PFT-1000 with fully atomically isolated Ni active sites. In contrast, pyrolysis of PTF-ZnNi20 or PTF-Ni-100 led to porous carbon catalysts containing nickel nanoparticles (Ni NPs) because of the very limited spatial separation of Ni-N-4 units with or without Zn-N-4, allowing Ni migration and aggregation to occur. Consequently, porous Ni-5-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, Ni-20-PFT-1000 and Ni-100-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.

Automated summary

This study presents a method for preparing highly efficient CO2 electroreduction catalysts using a spatial sites separation strategy. The catalyst with fully atomically isolated metal active sites was successfully achieved, showing high activity in converting CO2 to CO with high Faradaic efficiency and turnover frequency.