Ruthenium Assemblies for CO2 Reduction and H2 Generation: Time Resolved Infrared Spectroscopy, Spectroelectrochemistry and a Photocatalysis Study in Solution and on NiO.

Florian J R Cerpentier,Gregory M Greetham,Joshua Karlsson,Michael P Brandon,Elizabeth A Gibson,Mary T Pryce,Igor V Sazanovich,Ralte Lalrempuia

doi:10.3389/fchem.2021.795877

Abstract

Two novel supramolecular complexes RuRe ([Ru(dceb)2(bpt)Re(CO)3Cl](PF6)) and RuPt ([Ru(dceb)2(bpt)PtI(H2O)](PF6)2) [dceb = diethyl(2,2′-bipyridine)-4,4′-dicarboxylate, bpt = 3,5-di(pyridine-2-yl)-1,2,4-triazolate] were synthesized as new catalysts for photocatalytic CO2 reduction and H2 evolution, respectively. The influence of the catalytic metal for successful catalysis in solution and on a NiO semiconductor was examined. IR-active handles in the form of carbonyl groups on the peripheral ligand on the photosensitiser were used to study the excited states populated, as well as the one-electron reduced intermediate species using infrared and UV-Vis spectroelectrochemistry, and time resolved infrared spectroscopy. Inclusion of ethyl-ester moieties led to a reduction in the LUMO energies on the peripheral bipyridine ligand, resulting in localization of the 3MLCT excited state on these peripheral ligands following excitation. RuPt generated hydrogen in solution and when immobilized on NiO in a photoelectrochemical (PEC) cell. RuRe was inactive as a CO2 reduction catalyst in solution, and produced only trace amounts of CO when the photocatalyst was immobilized on NiO in a PEC cell saturated with CO2.

Highlights

The transition to renewable energy has become a key global objective due to the dwindling supply of fossil fuels, as well as the detrimental effect they have on the environment
Two novel supramolecular photocatalysts RuRe and RuPt were synthesized for CO2 reduction and H2 evolution, respectively
Time-resolved infrared spectroscopy on the picosecond to nanosecond timescale was used to probe the nature of the excited state

Summary

INTRODUCTION

The transition to renewable energy has become a key global objective due to the dwindling supply of fossil fuels, as well as the detrimental effect they have on the environment. In the case of the ester anchoring groups employed by us, they lower the triplet metal to ligand charge transfer (3MLCT) excited state localized on the peripheral ligand resulting in increased electron density on the peripheral ligands in the excited state While this reduces electron transfer to the metal centre via the bridging ligand (Tschierlei et al, 2010; Karnahl et al, 2011; Singh Bindra et al, 2012; Zedler et al, 2019), it might aid in storing the two reductive equivalents required for catalysis (Pan et al, 2016; Põldme et al, 2019). This helped us to assign the localization of the excited states following excitation

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT