Intramolecular Electron Transfer Governs Photoinduced Hydrogen Evolution by Nickel-Substituted Rubredoxin: Resolving Elementary Steps in Solar Fuel Generation

Abstract

The field of solar fuels is a rapidly growing area of research, though low overall efficiencies continue to preclude large-scale implementation. To resolve the elementary processes involved in lightdriven energy storage and identify key factors contributing to efficiency losses, systematic investigation and optimization are necessary. In this work, a ruthenium chromophore is directly attached to a model hydrogenase enzyme, nickel-substituted rubredoxin, to construct a molecular system capable of photoinduced hydrogen evolution. Timeresolved absorption and emission spectroscopy reveal direct, rapid intramolecular electron transfer (ET) between the two metal centers to generate a charge-separated state that persists for ∼1 μs, though this species is not productive for hydrogen evolution. Investigation of the photochemical behavior under catalytic conditions in conjunction with thermochemical analyses suggests that ET to the catalytic nickel site from the reductively quenched ruthenium center is the rate-determining step. By eliminating the need for three components to diffuse together, direct mechanistic information about catalysis is obtained in a time-resolved manner. This approach is generalizable to study the activity and intramolecular charge transfer properties of a wide range of photosensitizers and catalysts, with applicability toward diverse energy conversion reactions.

Native Protein Template Assisted Synthesis of Non-Native Metal-Sulfur Clusters

“…The hydrogen production efficiency is lowest when the Ru-chromophore is the longest distance from the Ni-active Ni-Rd is also extended to design hybrid catalysts for light-driven H 2 evolution, namely "solar fuel", which is an emerging research area [90][91][92][93]. In order to meet this, a rutheniumbased chromophore is covalently connected to mutated Ni-Rd through free Cys31 residue to build a hybrid enzyme, Ru,Ni-Rd, that is capable of photo-induced hydrogen production [87,94]. The hydrogen generation rate highly depends on the distance between Ru and Ni centers in Ru,Ni-Rd suggesting the intramolecular electron transfer in catalysis.…”

Light‐driven catalysis with engineered enzymes and biomimetic systems

“…Although most hydrogenase mimicry has focused on the diiron hydrogenase, one of the earliest systems was based on the [NiFe] hydrogenase [155][156][157][158][159][160][161]. Substitution of Ni in rubredoxin yields a catalyst, Ni-Rd, with a tetrathiolate active site mimicking the primary coordination sphere of the Ni site in [NiFe] hydrogenase [155,161].…”

“…The protein structure is amenable to many different mutations, opening the possibility for optimization [160]. In further work, a ruthenium sensitizer was covalently attached to the protein scaffold, creating an integrated hydrogen evolution system [159].…”

3D-Cobalt-Dicyanamide-Derived 2D-Layered-Co(OH)2-Based Catalyst for Light-Driven Hydrogen Evolution

“…The majority of HER photocatalytic systems consist of a catalyst, a photosensitizer (PS), and a sacrificial electron donor. Various PSs have been developed, including organic and organometallic chromophores, which serve as both a light absorber and an electron carrier for the catalyst. ,− Among them, ruthenium PSs have commonly been used for visible-light-driven HER studies due to their unique redox and photochemical properties. − While metallic colloidal Pt or Pt-containing catalysts display excellent HER activity, they are rare and expensive. , Earth-abundant metals such as cobalt, nickel, iron, and copper have gained significant attraction as potential HER catalysts over the past decades. ,, …”