Optimizing Electron Densities of Ni‐N‐C Complexes by Hybrid Coordination for Efficient Electrocatalytic CO₂ Reduction

Abstract

Metal‐N‐C is a type of attractive electrocatalyst for efficient CO2 reduction to CO. Because of the ambiguity in their atomic structures, the active sites and catalytic mechanisms of the catalysts have remained under debate. Here, the effects of N and C hybrid coordination on the activity of Ni‐N‐C catalysts were investigated, combining theoretical and experimental methods. The theoretical calculations revealed that N and C hybrid coordination greatly enhanced the capability of single‐atom Ni active sites to provide electrons to reactant molecules and strengthens the bonding of Ni to N and C in the Ni‐N‐C complexes. During the reaction process, the C and N coordination synergistically optimized the reaction energies in the conversion of CO2 to CO. A good agreement between theoretical calculations and electrochemical experiments was achieved based on the newly developed Ni‐N‐C electrocatalysts. The activity of hybrid‐coordination NiN2C2 was more than double that of single‐coordination NiN4.

Confining Chainmail‐Bearing Ni Nanoparticles in N‐doped Carbon Nanotubes for Robust and Efficient Electroreduction of CO2

“…Such durability was much better than Ni@NC/NCNT, Ni@NC and NCNT (Figure S7c and d). More importantly, our catalyst surpassed most state‐of‐the‐art CO‐selective catalysts in terms of long‐term durability in CO 2 RR (Figure 4f and Table S7) [16,17,19,26,33–35,37,60,66,67,69,72,76–94] . These unambiguously demonstrated the advantage of the dual chainmail structure in reinforcing the catalyst and boosting the CO 2 RR performance.…”

“…The results here further proved the lower energy barrier and thus higher activity of Ni@NC@NCNT towards CO 2 RR to produce CO. Moreover, the specific value of 118 mV dec −1 revealed that the rate‐determining step for Ni@NC/NCNT was the initial electron transfer process to form CO 2 .− or the concerted electron‐proton process to form * COOH [32,80–82] . To further determine whether a proton participated in the rate‐determining step, the reaction order of CO 2 RR with respect to bicarbonate was investigated.…”

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…The experimental data corroborated the theoretical predictions, since Ni-N-C materials containing mixed N/C coordination synthesized at intermediate carbonization temperatures provided the best results in terms of activity and selectivity towards CO production. 320 Interestingly, the coordinative motif of Ni-N 2 C 2 moieties homogeneously dispersed on a 2D graphene layer shows structural analogies with an efficient homogeneous Ni catalyst bearing a macrocyclic ligand based on a redox-active 2,2 0 -bipyridyl core and electron-rich N-heterocyclic carbene (NHC) donors , previously discussed in the Section 4.2. 258 In particular, the optimal 15-membered macrocyclic configuration forced the molecular Ni system 54-Ni to a distorted square-planar arrangement which is consistent with synchrothron-based experimental data on analogous Ni-N 2 C 2 SACs.…”

“…258 In particular, the optimal 15-membered macrocyclic configuration forced the molecular Ni system 54-Ni to a distorted square-planar arrangement which is consistent with synchrothron-based experimental data on analogous Ni-N 2 C 2 SACs. 320 For the molecular Ni derivative 54-Ni, the contribution of the quasi-planar ligand environment to extra-electron delocalization revealed to be decisive to prevent the formation of a metal-hydride species.…”

“…By using theoretical and experimental tools, Yamauchi and co-workers systematically investigated a series of hybrid Ni-N x C 4Àx (x = 0-4) moieties containing different combinations of coordinating N or C atoms in an attempt to elucidate the role of C atoms on the structural and catalytic properties of Ni N-C SACs. 320 For each configuration, the thermodynamic barrier associated to each of the three elementary steps of the CO 2 RR pathway were compared, i.e. the *COOH formation (* + CO 2 + H + + e À -*COOH), the *CO formation (*COOH + H + + e À -*CO + H 2 O) and CO desorption (*CO -* + CO).…”