Photoelectrochemical H2 Evolution with a Hydrogenase Immobilized on a TiO2 -Protected Silicon Electrode

Abstract

The combination of enzymes with semiconductors enables the photoelectrochemical characterization of electron-transfer processes at highly active and well-defined catalytic sites on a light-harvesting electrode surface. Herein, we report the integration of a hydrogenase on a TiO2 -coated p-Si photocathode for the photo-reduction of protons to H2 . The immobilized hydrogenase exhibits activity on Si attributable to a bifunctional TiO2 layer, which protects the Si electrode from oxidation and acts as a biocompatible support layer for the productive adsorption of the enzyme. The p-Si|TiO2 |hydrogenase photocathode displays visible-light driven production of H2 at an energy-storing, positive electrochemical potential and an essentially quantitative faradaic efficiency. We have thus established a widely applicable platform to wire redox enzymes in an active configuration on a p-type semiconductor photocathode through the engineering of the enzyme-materials interface.

Keywords: TiO2; hydrogen evolution; hydrogenase; photoelectrochemistry; semiconductors.

Figure 1

Schematic representation of the p‐Si|TiO₂|hydrogenase photocathode. The amorphous TiO₂ acts as a bifunctional interface layer as it protects Si from the formation of an insulating oxide coating and provides a biocompatible surface to facilitate the adsorption of Dmb [NiFeSe]‐hydrogenase. VB=valence band, CB=conduction band, E _f=Fermi level.

Figure 2

Protein film electrochemistry with FTO|TiO₂|hydrogenase. The voltammograms were recorded for a stirred sample, under an atmosphere of N₂ (blue trace) and 1 bar H₂ (red trace) at a scan rate of 10 mV s⁻¹. A control experiment (black trace) in the absence of enzyme is also shown. The inset shows the CPE trace at E _appl=−0.35 V versus SHE under N₂ for FTO|TiO₂ (black) and FTO|TiO₂|hydrogenase (blue). All experiments were performed in MES (50 mm) electrolyte solution with a Ag/AgCl reference and Pt counter electrode at pH 6.0 at 20±2 °C.

Figure 3

Protein film photoelectrochemistry with p‐Si|TiO₂|hydrogenase. a) Photoresponse under chopped irradiation (10 mW cm⁻²; gray shading indicates response in the dark) performed at a scan rate of 10 mV s⁻¹ under a N₂ atmosphere. b) CPE at E _appl=−0.35 V versus SHE (pH 6.0) during irradiation under a N₂ atmosphere; the color labeling of the traces from (a) applies also to the CPE traces in (b). Inset shows the effect of 10 % CO injections (highlighted in gray) on the photocurrent response of p‐Si|TiO₂|hydrogenase at E _appl=−0.35 V versus SHE, followed by flushing with 100 % N₂. All experiments were performed in MES (50 mm) electrolyte solution with a Ag/AgCl reference and Pt counter electrode at pH 6.0 at 20±2 °C under white‐light illumination with an intensity of 10 mW cm⁻².