Abstract
The biological formate hydrogenlyase (FHL) complex links a formate dehydrogenase (FDH) to a hydrogenase (H2ase) and produces H2 and CO2 from formate via mixed-acid fermentation in Escherichia coli. Here, we describe an electrochemical and a colloidal semiartificial FHL system that consists of an FDH and a H2ase immobilized on conductive indium tin oxide (ITO) as an electron relay. These in vitro systems benefit from the efficient wiring of a highly active enzyme pair and allow for the reversible conversion of formate to H2 and CO2 under ambient temperature and pressure. The hybrid systems provide a template for the design of synthetic catalysts and surpass the FHL complex in vivo by storing and releasing H2 on demand by interconverting CO2/H2 and formate with minimal bias in either direction.
Highlights
H2 is a promising fuel in a carbon-neutral economy and its conversion to formate allows for easier storage and transport
H2 gas cleanly separates from dissolved formate, and their interconversion comes at little thermodynamic cost.[6,7]
Desulfovibrio vulgaris Hildenborough can grow by converting formate to H2,23 with formate oxidation catalyzed by a periplasmic formate dehydrogenase (FDH), and H2 produced either via direct or transmembrane electron transfer.[24]
Summary
Communication individual enzymes, high and matching current densities, and good stability make this enzyme pair a promising candidate for assembling a reversible HCO2−/H2 interconversion system.[6] the IO-ITO|FDH (working electrode) was wired to the IO-ITO|H2ase (counter electrode) in a two-electrode configuration (Figure 2b). ITO|H2ase cell with formate present (Figure 2c) produced H2 (5.84 ± 0.88 μmol cm−2) with ηF of (79 ± 11)%. CPE at Uapp = −0.2 V for 2 h with H2 present generated formate (5.00 ± 0.80 μmol cm−2) with ηF of (81 ± 15)% This semiartificial electrochemical FHL system exhibited good stability, retaining >95% of its initial activity after 2 h in both directions. A high concentration of the cytochrome (1.9 μM, 100-fold excess vs FDH) was required to achieve comparable kinetics of H2 and formate production (Figure S11a,b), revealing the superiority of coimmobilizing the two enzymes on synthetic ITO NPs to achieve efficient electron transfer.
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