Swapping CO₂ electro-reduction active sites on a nickel-based hybrid formed on a "guilty" covalent triazine framework

A homogeneous and almost monodisperse Ni/CTF^ph composite of ultrasmall Ni NPs (∼2.2 nm) has been prepared by Metal Vapor Synthesis (MVS) and deposited on a highly porous and high specific surface area covalent triazine network. Metal doping was deliberately carried out on a metal-free system exhibiting superior CO₂RR selectivity towards the challenging CO₂-to-HCOOH electroreduction. Electrochemical studies aimed at shedding light on the CO₂RR performance of the ultimate composite have allowed speculation on the synergistic or exclusive action of the two potentially active phases (N-doped C-network vs. Ni NPs). In contrast to the generally exclusive CO₂-to-CO reduction mechanism described for the state-of-the-art Ni NP-based CO₂RR electrocatalysts, Ni/CTF^ph has unveiled the unprecedented ability of Ni NPs to promote the alternative and more challenging 2e^- CO₂-to-HCOOH reduction pathway, even at moderately reducing potentials (-0.3 V vs. RHE).