Selective CO Production in Photoelectrochemical Reduction of CO₂ with a Cobalt Chlorin Complex Adsorbed on Multiwalled Carbon Nanotubes in Water

Abstract

Photoelectrochemical reduction of CO 2 occurred using cobalt(II) chlorin (Co II (Ch)) as a cathode active material adsorbed on multiwalled carbon nanotubes as a current collector in combination with a surface-modified BiVO 4 photoanode with iron(III) oxide(hydroxide), FeO(OH), to produce CO with 83% Faradaic efficiency at an applied bias voltage of −1.3 V at the Co II (Ch)-modified cathode vs the FeO(OH)/BiVO 4 /FTO photoanode under visible light irradiation in a CO 2 -saturated aqueous solution (pH 4.6). The difference in the oxidation potential of the FeO(OH)/BiVO 4 /FTO electrode under dark and that under light illumination was ∼1.5 V, which was smaller than the band gap of BiVO 4 (band gap energy ≈ 2.4 eV), indicating that the FeO(OH)/ BiVO 4 /FTO photoanode lowered the total bias that enabled simultaneous water oxidation and CO 2 reduction.

Immobilization of Molecular Catalysts for Enhanced Redox Catalysis

“…Immobilization of a cobalt(II) chlorin complex [Co II (Ch)] on multi‐walled carbon nanotubes (MWCNTs) also resulted in significant improvement of the catalytic activity and selectivity for the photocatalytic CO 2 reduction with triethylamine (TEA) in competition with the proton reduction to H 2 by use of [Ru II (Me 2 phen) 3 ] 2+ (Me 2 phen=4,7‐dimethyl‐1,10‐phenanthroline) as a photocatalyst in MeCN containing H 2 O (v/v 5 %) to yield CO and H 2 with a 2.4 to 1.0 ratio with a TON of 710 . The π ‐ π interaction between MWCNTs and Co II (Ch) provided a hydrophobic environment suitable for binding CO 2 instead of proton, resulting in the selective reduction of CO 2 to CO rather than the reduction of proton to H 2 …”

“…[172] The p-p interaction between MWCNTsa nd Co II (Ch) provideda hydrophobic environments uitablef or binding CO 2 instead of proton, resulting in the selectiver eductiono fC O 2 to CO rather than the reduction of protontoH 2 . [173][174][175][176] When [(tpa)Mn II ] 2 + (tpa = tris(2-pyridylmethyl)amine) was immobilized on Al-MCM-41,t he immobilized [(tpa)Mn II ] 2 + @Al-MCM-41 catalyzed selective hydroxylation of benzene with H 2 O 2 to produce phenol selectively without further oxidation at ambient temperature as shown in Figure 19. [177] In contrast, no benzene oxidationo ccurred by use of Mn 2 + @Al-MCM-41, [(tpa) 2 Mn 2 (m-O) 2 ] 3 + @Al-MCM-41, or [(tpa)Mn II ] 2 + under the same reactionc onditions.…”

Role of Heteroatoms in S,N‐Codoped Nanoporous Carbon Materials in CO2 (Photo)electrochemical Reduction

“…The FE for CO formation at 5h was 27.0 % and 4.4 %f or BAX-TU-950 andB AX-TU-600, respectively. [38] On a Co II (Ch)-modified cathode,t he highestr ate measured was 0.58 mmol h À1 at pH 6.7 [39] and on Agloadedb oron-doped diamond (BDD) electrodes, the reported rate was 5.97 mmol h À1 . Althought he partial CO current density of BAX-TU-950 increased 21 %, for BAX-TU-600 that increase was 28 %, in comparison to those measured in the dark (Figure 10 b).…”

Recent Progress on Photo‐Electrocatalytic Reduction of Carbon Dioxide

“…Very recently, a BiVO 4 ‐based photoanode‐driven system was developed using iron(III) oxide(hydroxide) (FeOOH) modified BiVO 4 as a photoanode and cobalt(II) chlorin (CoII(Ch)) modified multiwalled carbon nanotubes (MWCNTs) as a cathode to produce CO with 83% Faradaic efficiency at an applied voltage of −1.3 V on the MWCNTs/CoII(Ch) cathode vs the BiVO 4 /FeOOH photoanode under visible light irradiation in a CO 2 ‐saturated aqueous solution (pH 4.6) . The BiVO 4 /FeOOH photoanode provides a voltage compensation, lowering the total bias to drive the simultaneous water oxidation and CO 2 reduction.…”