Electrocatalytic and Photocatalytic Reduction of CO₂ to CO by Cobalt(II) Tripodal Complexes: Low Overpotentials, High Efficiency and Selectivity

Abstract

The reduction of carbon dioxide (CO ) has been considered as an approach to mitigate global warming and to provide renewable carbon-based fuels. Rational design of efficient, selective, and inexpensive catalysts with low overpotentials is urgently desired. In this study, four cobalt(II) tripodal complexes are tested as catalysts for CO reduction to CO in a MeCN/H O (4:1 v/v) solution. The replacement of pyridyl groups in the ligands with less basic quinolinyl groups greatly reduces the required overpotential for CO -to-CO conversion down to 200-380 mV. Benefitting from the low overpotentials, a photocatalyst system for CO -to-CO conversion is successfully constructed, with an maximum turnover number (TON) of 10 650±750, a turnover frequency (TOF) of 1150±80 h , and almost 100 % selectivity to CO. These outstanding catalytic performances are further elucidated by DFT calculations.

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

“…277 The beneficial effect of visible-light irradiation on catalysis was further demonstrated by a substantial improvement of the observed FE for CO production during bulk electrolysis upon irradiation, suggesting that light-assisted electrocatalysis is an effective strategy to alleviate CO inhibition limitation. It is also worth noting that several reported Co aminopyridyl catalysts showed optimal performances under photochemical 273,274,278,279 or photoelectrochemical 280 conditions compared to pure electrochemical conditions.…”

“…Contrariwise, the other complexes of the series supported by similar ligands displayed very poor electrocatalytic properties for CO 2 RR, resulting in the formation of only traces of CO. 273 In another comparative study, a family of tripodal Co II complexes containing pyridyl or less basic quinolyl groups displayed variable ability for a selective CO 2 -to-CO conversion under electrochemical conditions, with the complexes 60 and 61 showing the best performances (FE CO = 58-72% and 84%, respectively). 274 Furthermore, a number of polypyridyl Co complexes were reported to suffer from very low faradaic yields for CO production (r30%), 275,276 which are not related to competitive HER or to alternative CO 2 RR pathways. In addition, moderate durability in long-term electrolysis is generally reported even for some CO-selective Co systems, suggesting a possible CO deactivation pathway.…”

CoIICryptates Convert CO2into CO and CH4under Visible Light

“…Apart from cryptates, cyclams and their derivatives, [6,10,35] porphyrins and somea nalogues, [12,13,36,37] polypyridyl [23,38,39] and other [30,33,[40][41][42][43] ligandsh ave been associated with cobalt to photoreduceC O 2 .F or instance, Tinnemans et al [10] used Co II and Co III complexes bearing diamine macrocyclic ligands as catalysts, with [Ru(bipy) 3 ] 2 + as PS and ascorbic acid as SED, leadingt ot he observation of CO and H 2 with al ow CO selectivity of < 35 %a nd turnover number (TON) values below 350.…”

“…Apart from cryptates, cyclams and their derivatives, porphyrins and some analogues, polypyridyl and other ligands have been associated with cobalt to photoreduce CO 2 . For instance, Tinnemans et al .…”

Unexpected Effect of Intramolecular Phenolic Group on Electrocatalytic CO2 Reduction

“…Recent efforts have led to the identification of a variety of cheap and earth-abundant transition metal complexes as active molecular catalysts. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Fe porphyrins have received considerable attention among these catalysts. They show high activity and stability for the selective CO 2 -to-CO conversion, and they provide an ideal platform to investigate various structural effects on CO 2 RR, because the meso-substituents of the porphyrin ring can be systematically modified to introduce different acid/base groups and positively/negatively charged moieties.…”