Design of photoelectrochemical cells for biocatalytic selective oxyfunctionalization

Abstract

Drawing inspiration from natural photosynthesis, biocatalytic photoelectrochemical (PEC) platforms have gained prominence for the conversion of solar energy into useful chemicals by combining redox biocatalysis and photoelectrocatalysis. This thesis describes the design strategies of photoelectrochemical platforms to provide peroxygenases with suitable amounts of $H_2O_2$ for efficient solar-to-chemical conversion while minimizing the undesired $H_2O_2$-mediated peroxygenase inactivation. Chapter 1 provides an overview in light-driven activation of oxidoreductases through direct or indirect transfer of photoinduced electrons. The approaches and understanding in the construction of catalytic assemblies to activate redox enzymes using photosensitizers and photoelectrochemical platforms are outlined. This chapter describes current technical challenges and strategies to advance photobiocatalytic transformation as a synthetic tool. Chapter 2 describes a photoelectrochemical approach to provide peroxygenases with suitable amounts of $H_2O_2$ while reducing the electrochemical overpotential needed for the reduction of molecular oxygen to $H_2O_2$. The results suggests that flavin-single-walled carbon nanotube-based photoelectrochemical platform enables peroxygenases-catalyzed, selective hydroxylation reactions. Chapter 3 demonstrates an unbiased PEC tandem structure consisting of a $FeOOH$/$BiVO_4$ photoanode, a $Cu(In,Ga)Se_2$ solar absorber, and a graphitic carbon nitride/reduced graphene oxide hybrid cathode. Powered by sufficient photovoltage generated by the solar absorber, the PEC platform generates $H_2O_2$ in situ using water in the absence of external bias. The peroxygenase catalyzed the hydroxylation of ethylbenzene to (R)-1-phenylethanol with total turnover numbers over 43,300 ($ee > 99%$) in the unbiased PEC tandem system. In Chapter 4, a dual biocatalytic PEC platform is constructed, which consisted of a $Mo$-doped $BiVO_4$ photoanode and a hierarchical porous #ITO# cathode that gives rise to the coupling of peroxygenase and ene reductase-mediated catalysis, respectively. This chapter shows a new type of biocatalytic PEC platform to produce value-added chemicals on both sides using solar energy and water with the deliberate integration of enzymatic redox processes.