Advanced Ni-N_x-C single-site catalysts for CO₂ electroreduction to CO based on hierarchical carbon nanocages and S-doping

Metal-nitrogen-carbon materials are promising catalysts for CO₂ electroreduction to CO. Herein, by taking the unique hierarchical carbon nanocages as the support, an advanced nickel-nitrogen-carbon single-site catalyst is conveniently prepared by pyrolyzing the mixture of NiCl₂ and phenanthroline, which exhibits a Faradaic efficiency plateau of > 87% in a wide potential window of -0.6 - -1.0 V. Further S-doping by adding KSCN into the precursor much enhances the CO specific current density by 68%, up to 37.5 A·g^-1 at -0.8 V, along with an improved CO Faradaic efficiency plateau of > 90%. Such an enhancement can be ascribed to the facilitated CO pathway and suppressed hydrogen evolution from thermodynamic viewpoint as well as the increased electroactive surface area and improved charge transfer fromkinetic viewpoint due to the S-doping. This study demonstrates a simple and effective approach to advanced electrocatalysts by synergetic modification of the porous carbon-based support and electronic structure of the active sites.