Design of photoelectrochemical platforms for biocatalytic carbon dioxide reduction

Abstract

Biocatalytic $CO_2$ reduction is a promising route for sustainable $CO_2$ conversion because of exceptional chemoselectivity and stereospecificity as well as high yield at ambient conditions. Inspired by the Z-scheme photosynthesis scheme, the design strategies of photoelectrochemical platforms for efficient and sustainable biocatalytic $CO_2$ reduction are addressed.

Chapter 1 demonstrates a tandem-photoelectrochemical (PEC)-cell-integrated-with-enzyme-cascade (TPIEC) system, which transfers photogenerated electrons to a multi-enzyme cascade for biocatalyzed reduction of $CO_2$ to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide-based tandem PEC cell for visible light-assisted regeneration of nicotinamide cofactor (NADH). To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Using applied bias, the TPIEC system achieved high methanol conversion output using readily-available solar energy and water.

Chapter 2 describes a strongly $CO_2$-reductive, cofactor-independent formate dehydrogenase from Clostridium ljungdahlii (ClFDH) and a $CO_2$-to-formate converting bioelectrode by immobilizing ClFDH on a conductive polyaniline (PANi) scaffold. The 3D-nanostructured PANi hydrogel facilitated efficient enzyme immobilization and rapid electron injection to the active site of ClFDH. The W-containing ClFDH in the hybrid electrode successfully gained electrons from PANi and exhibited high capability for electroenzymatic conversion of $CO_2$ to formate at low overvoltage without NADH.

In Chapter 3, the design of a FDH-immobilized, direct electron transfer (DET)-type biocathode based on a continuous 3D structured TiN nanoshell (3D TiN) for $CO_2$-to-formate converting biocatalytic tandem PEC system is presented. The conductive 3D TiN possesses periodic porous networks with a large surface area and high porosity which are favorable for a large amount of enzyme loading and efficient DET to the adsorbed enzyme. At low overvoltage, the 3D TiN-ClFDH biocathode stably converted $CO_2$ into formate by DET with a high faradaic efficiency. Finally, 3D TiN-ClFDH biocathode was adopted to the $BiVO_4$/perovskite tandem PEC cell. The assembled biocatalytic tandem PEC cell exhibited solar-driven formate generation from $CO_2$ in ambient condition.