Fast and Selective Photoreduction of CO₂ to CO Catalyzed by a Complex of Carbon Monoxide Dehydrogenase, TiO₂, and Ag Nanoclusters

Abstract

Selective, visible-light-driven conversion of CO2 to CO with a turnover frequency of 20 s−1 under visible light irradiation at 25 °C is catalyzed by an aqueous colloidal system comprising a pseudoternary complex formed among carbon monoxide dehydrogenase (CODH), silver nanoclusters stabilized by polymethacrylic acid (AgNCs-PMAA), and TiO2 nanoparticles. The photocatalytic assembly, which is stable over several hours and for at least 250000 turnovers of the enzyme’s active site, was investigated by separate electrochemical (dark) and fluorescence measurements to establish specific connectivities among the components. The data show (a) that a coating of AgNCs-PMAA on TiO2 greatly enhances its ability as an electrode for CODH- based electrocatalysis of CO2 reduction and (b) that the individual Ag nanoclusters interact directly and dynamically with the enzyme surface, most likely at exposed cysteine thiols. The results lead to a model for photocatalysis in which the AgNCs act as photosensitizers, CODH captures the excited electrons for catalysis, and TiO2 mediates hole transfer from the AgNC valence band to sacrificial electron donors. The results greatly increase the benchmark for reversible CO2 reduction under ambient conditions and demonstrate that, with such efficient catalysts, the limiting factor is the supply of photogenerated electrons.

Direct visible light activation of a surface cysteine-engineered [NiFe]-hydrogenase by silver nanoclusters

“…To stabilize AgNCs, it is necessary to template them in a water-soluble matrix such as polymethacrylic acid (PMAA, average molecular mass 5 kDa, 60 monomer units) which can typically stabilize five AgNCs each containing o10 Ag atoms. [30][31][32][33] The free carboxylates on PMAA that are not used to bind AgNCs also allow simultaneous attachment to the hard-acid surface of metal oxide supports. 34,35 In a recent paper, we reported a much enhanced (100-fold) rate for CO formation by carbon monoxide dehydrogenase co-adsorbed on TiO 2 (Degussa P-25) nanoparticles that had been modified with AgNCs-PMAA, in which Ag 5 was the dominant species.…”

“…34,35 In a recent paper, we reported a much enhanced (100-fold) rate for CO formation by carbon monoxide dehydrogenase co-adsorbed on TiO 2 (Degussa P-25) nanoparticles that had been modified with AgNCs-PMAA, in which Ag 5 was the dominant species. 33 In this Communication, we report a systematic approach which exploits the ability to re-engineer a [NiFe]-hydrogenase for selective surface attachment of AgNCs leading to a 'hard-wired' photoactive enzyme. The experiments are developed and extended to help understand the charge flow in a highly efficient system for photohydrogen production.…”

Strategies for Bioelectrochemical CO2 Reduction

“…triethanolamine), and the enzyme captures the photoexcitede lectrons for catalysis in the presence of light;t he overall turnover frequency,l imited by excited electron availability to the catalyst, was greatly enhanced using this setup ( Figure 2B). [30] CdS nanocrystals have also been used to reduce CO 2 to CO in the presence of visible light. [31] Further,S hafaata nd colleagues have described an artificial metalloenzyme for CO 2 reduction to CO by incorporating an ickel complex, [Ni II (cyclam)] 2 + ,w ith azurin.…”

“…(B) CODHw ith AgNCs-PMMAc oadsorbed on aT iO 2 surface to enable efficient CO formationf rom CO 2 in the presenceo fv isible light. Reproduced with permission from AmericanC hemical Societyfrom Reference[30].…”

Production and properties of enzymes that activate and produce carbon monoxide

“…Over the past decade, we have also described various CODH-catalyzed nanoparticle systems that can rapidly and selectively reduce CO 2 to CO using visible light, most recently in 2018 (Zhang, Can, Ragsdale, & Armstrong, 2018). The studies demonstrate that CODH is remarkably reversible, showing catalytic activity close to the equilibrium redox potential for the CO 2 /CO couple (0.52V), i.e., operating selectively without any significant overpotential.…”