Cooperative Stabilization of the [Pyridinium-CO₂-Co] Adduct on a Metal–Organic Layer Enhances Electrocatalytic CO₂ Reduction

Abstract

Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO 2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobaltprotoporphyrin (CoPP) and pyridine/pyridinium (py/pyH + ) catalytic sites on metal−organic layers (MOLs) for an electrocatalytic CO 2 reduction reaction (CO 2 RR). Constructed from [Hf 6 (μ 3 -O) 4 (μ 3 -OH) 4 (HCO 2 ) 6 ] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH + ) moiety on the MOL coactivate CO 2 by forming the [pyH + -− O 2 C-CoPP] adduct, which enhances the CO 2 RR and suppresses hydrogen evolution to afford a high CO/ H 2 selectivity of 11.8. Cooperative stabilization of the [pyH + -− O 2 C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at −0.86 V RHE , which corresponds to a turnover frequency of 0.4 s −1 .

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

“…9). 168 Following a post-synthetic approach, CoPP moieties were incorporated into two different MOL backbone derivatives, built from benzenetribenzoate (BTB) and 4 0 -(4-benzoate)-(2,2 0 ,2 00 -terpyridine)-5,5 00dicarboxylate (TPY) linkers, respectively. In the TPY-MOL-CoPP material, the pyridine/pyridinium pendant groups adjacent to the CoPP active sites were found to engage a cooperative synergistic boosting effect on catalysis ( Fig.…”

“…9c). 168 DFT calculations suggested that the pyridinium moieties of the framework exert a cooperative boosting effect by lowering the energy barrier for both, CO 2 adsorption and C-O bond cleavage, the latter being the ratedetermining step of the process. The proposed mechanism is analogous to the one above mentioned for the Co porphine system, 154 whereby the one-electron reduction of CoPP to [CoPP] À is followed by CO 2 binding and protonation steps, leading to the formation of the key [pyH-O 2 C-Co(PP)] 0 adduct, stabilized by a pre-positioned pyridine moiety to favor CO 2 RR over HER.…”

“…A second electron uptake is then followed by the C-O bond cleavage to form the [Co(PP)(CO)] 0 species which undergoes CO release. 168 Finally, the efficiency of electron transport to the catalytic site is a crucial limiting factor to the usage of reticular systems for efficient CO 2 RR. 33 In this regard, the incorporation of electron carriers as building blocks of the framework has revealed to be an effective strategy to improve electron migration in COFs.…”

Facile electron delivery from graphene template to ultrathin metal-organic layers for boosting CO2 photoreduction

“…Nanosizing MOFs into ultrathin metal-organic layers (MOLs) can e ciently accelerate mass transport / electron transfer and create abundant readily accessible active sites to ensure high activity in various catalytic reactions. [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Moreover, ultrathin MOFs with limited number of atoms represent ideal models to explore structure-performance relationships for further rationally constructing e cient catalysts at atomic/molecular levels. For example, a mono-carboxylic bipyridine ligand was utilized to assemble Re-/Mn-Ru molecules into monolayer Hf-based MOLs, 20 the resulting Re-Ru-based MOLs can sustainably reduce CO 2 to CO under real sunlight for one week.…”

Surface Chemistry Modulates CO2 Reduction Reaction Intermediates on Silver Nanoparticle Electrocatalysts

“…Secondary coordination sphere effects, routinely employed by enzymes, 7 have been translated to both molecular 8,9 and heterogeneous [10][11][12][13] CO2R electrocatalysts. In the context of heterogeneous systems, CO2R performance has been successfully modulated through the use of grafted surface ligands which interact with adsorbed species or promote their transfer to the catalyst surface, [14][15][16][17][18][19] design of enzyme-mimetic catalytic pockets in porous materials, 20,21 and tuning of the electrolyte. [22][23][24] Complementary to CO2R system design is the innovation of operando techniques which provide mechanistic information on the reaction and are performed simultaneously as the reaction proceeds.…”