Understanding and Tuning Charge Dynamics in Carbon Nitride/Cobalt(II) Complex Hybrids for Enhanced Photocatalytic CO₂ Reduction

Abstract

Semiconductor/metal complex hybrids are promising photocatalysts for CO2 reduction. A comprehensive mechanism investigation on charge dynamics was carried out for a hybrid g-C3N4/[Co(bpy)3]2+ (bpy = 2,2′-bipyridine) photocatalytic system by using a combination of in situ UV–vis and resonance Raman spectroscopies, electrochemistry, and spectroelectrochemistry. A singly reduced [Co(bpy)2]+ species binding to CO2 was directly identified as an important intermediate. The excessive accumulation of this transformed [CoIII(bpy)2CO2]+ intermediate indicates that the subsequent CO2 reduction reaction is the main rate-limiting process. Built on these findings, the heterosystem was modified to g-C3N4/[Co(dmbpy)3]2+, where dmbpy = 4,4′-dimethyl-2,2′-bipyridine. The electron affinity of the cobalt complex segment and thereby the specific CO2 binding were enhanced. The refined charge dynamics led to 5.4 times enhanced photocatalytic CO2-to-CO conversion, with a selectivity of over 85% and an apparent quantum yield of 1.96% at 400 nm. This study provides an applicable spectroscopic approach to investigate in-depth charge-transfer characteristics and identify the main rate-limiting process, as well as shows the significance of rational design based on mechanism understanding.

A robust Fe-based heterogeneous photocatalyst for the visible-light-mediated selective reduction of an impure CO2 stream

“…Recently, graphitic carbon nitrides (g-C 3 N 4 ) have become highly attractive as photocatalysts due to their high chemical and thermal stability, appropriate band structures, and low cost. 45–51 Thus, researchers have employed g–C 3 N 4 –based hybrid photocatalysts (g-C 3 N 4 combined with Ru, 52 Co, 53–56 and Fe 57–59 -based metal complexes) to improve the selectivity and reactivity for the reduction of CO 2 into CO (Scheme 1b). Among them, Co-based transition metal complexes such as [Co(bpy) 3 ] 2+ and Co(qpy) along with g-C 3 N 4 , exhibited the selectivity of 86 and 98% (TON of CO were 3.7 and 128, with the production rate of 37 and 7.98 μmol g −1 h −1 respectively) for the formation of CO in the presence of triethanolamine (TEOA) and 1,3-dimethyl-2-phenyl-2,3-dihydro-1 H -benzo[ d ]imidazole (BIH) as sacrificial reductant.…”

Anchoring of NiCox alloy nanoparticles on nitrogen vacancy-rich carbon nitride nanotubes toward promoting efficiently photocatalytic CO2 conversion into solar fuel

“…Fe, Cu, In, and MnCo) has been used to prolong the electron lifetime. 25–29 Nevertheless, these strategies have exhibited elevated selectivity for CO but are incapable of effective CH 4 production. Noble metals appear to be the best active sites for promoting photocatalytic CO 2 to CH 4 conversion.…”

Highly selective CO2 electrolysis in aqueous media by a water-soluble cobalt dimethyl-bipyridine complex

“…13 In the case of the bpy ligand, [Co(bpy) 3 ] 2+ ([Co-bpy]) or [Co(dmbpy) 3 ] 2+ ([Codmbpy], dmbpy: 4,4 0 -dimethyl-2,2 0 -bipyridine) has been shown to promote the CO 2 RR to produce CO and H 2 under visible-light irradiation when used in combination with a photosensitizer or a semiconductor photocatalyst in an acetonitrile (MeCN) or MeCN/H 2 O mixture containing sacrificial electron donor reagents. [14][15][16][17] We recently adopted a water-soluble [Co-dmbpy] (Fig. 1a) for Z-schematic (two-step photoexcitation) photocatalysis for the CO 2 RR in an aqueous suspension with two coexisting semiconductors (BiVO 4 for water oxidation and (CuGa) 0.3 Zn 1.4 S 2 for the CO 2 RR).…”