Covalently Grafting Cobalt Porphyrin onto Carbon Nanotubes for Efficient CO₂ Electroreduction

Abstract

Molecular complexes with inexpensive transitionmetal centers have drawn extensive attention, as they show ah igh selectivity in the electrochemical conversion of CO 2 to CO.Inthis work, we propose anew strategy to covalentlygraft cobalt porphyrin onto the surface of ac arbon nanotube by as ubstitution reaction at the metal center.M aterial characterization and electrochemical studies reveal that the porphyrin molecules are well dispersed at ahigh loading of 10 wt. %. As aresult, the turnover frequency for CO formation is improved by af actor of three compared to traditional physically-mixed catalysts with the same cobalt content. This leads to an outstanding overall current density of 25.1 mA cm À2 and aF aradaic efficiency of 98.3 %a t4 90 mV overpotential with excellent long-term stability.T his work provides an effective pathway for the improvement of the performance of electrocatalysts that could inspire rational design of molecular catalysts in the future.

Mechanistic Insights into Co and Fe Quaterpyridine-Based CO2 Reduction Catalysts: Metal–Ligand Orbital Interaction as the Key Driving Force for Distinct Pathways

“…24 Alternatively, activity can be improved by incorporating the catalyst into metal/covalent organic frameworks [25][26][27][28] or attaching the molecular catalyst onto a surface. [29][30][31][32][33][34] Mechanistic insights in the catalytic pathway are invaluable for rational catalyst design as they illuminate the origin of activity and selectivity, as well as the cause of any intrinsic limitations. Both spectroscopic methods and computational chemistry should be employed to identify possible intermediates, steps in the reaction pathway, activation barriers, and rate limiting steps.…”

Electroreduction of Carbon Dioxide by Heterogenized Cofacial Porphyrins

“…Furthermore, a CO 2 reaction order of approximately 1 is determined for all the catalysts, indicating the CO 2 -to-*COOH transformation to be the rate-limiting step (Fig. S10) [9]. *COOH formation is the most energy-demanding, as suggested by the DFT results, associated with the highest energy barrier of + 0.6 eV compared to other reaction steps (Fig.…”

“…Besides, the electronic structure of the catalytically active metal center, coordinated with four nitrogen atoms, could be effectively tuned by the surrounding ligands [1][2][3][4]. So far, there have been a variety of porphyrin-based molecular catalysts reported active for oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and CO 2 electroreduction (CO 2 RR) [5][6][7][8][9].…”

Emergence of CO2 electrolyzers including supported molecular catalysts

“…[26] Direct chemical bonding (or covalent grafting) of the catalyst to the support has been investigated, such as phosphonate linkage to a metal oxide [27,28] or via diazonium and amide chemistry. [29] Such approach was developed by Zhu et al, [30] for grafting a Co protoporphyrin at carbon nanotubes through covalent linkage between the support and the cobalt atom of the complex. It led to a current density for CO2 reduction in an H-cell close to the substrate mass transfer limiting value (vide infra).…”