Proton Reduction using a Hydrogenase-Modified Nanoporous Black Silicon Photoelectrode.

Metalloenzymes featuring earth-abundant metal-based cores exhibit rates for catalytic processes such as hydrogen evolution comparable to those of noble metals. Realizing these superb catalytic properties in artificial systems is challenging owing to the difficulty of effectively interfacing metalloenzymes with an electrode surface in a manner that supports high charge transfer rates. Here, we demonstrate that a nanoporous "black" silicon (b-Si) photocathode provides a unique interface for binding an adsorbed [FeFe]-hydrogenase enzyme ([FeFe]-H2ase). The resulting b-Si/[FeFe]-H2ase photoelectrode displays a 280 mV lower onset potential for hydrogen generation than bare b-Si without hydrogenase, similar to that observed for a b-Si/Pt photoelectrode at the same light intensity. Additionally, we show that this b-Si/H2ase electrode exhibits a turnover frequency of ≥1300 s-1, a turnover number above 107, and sustains current densities of at least 1 mA/cm2 based on the actual surface area of the electrode (not the smaller projected geometric area), orders of magnitude greater than that observed for previous enzyme-catalyzed electrodes. While the long-term stability of hydrogenase on the b-Si surface remains too low for practical applications, this work provides proof-of-concept that biologically-derived metalloenzymes can be interfaced with inorganic substrates to support technologically relevant current densities.