(Invited) Solar-Driven CO2 Reduction By Molecular-Semiconductor Hybrid Systems: Photoelectrodes and Particulate Photocatalysts

Abstract

For the development of photosystem for CO2 reduction into useful energy-rich chemicals using water as an electron donor operating under sunlight irradiation, the combination of a semiconductor photosensitizer and a metal-complex catalyst is one promising approach. We previously proposed the a hybrid molecular-catalyst/semiconductor system for the visible-light driven CO2 reduction, and demonstrated particulate photocatalyst and photoelectrode systems utilizing Ru-bipyridine complexes and their polymers as catalysts contacted with semiconductors of N-doped Ta2O5[1], GaP:Zn [2], InP:Zn[2], (CuGa)0.8Zn0.4S2[3], (AgIn)0.22Zn1.56S2[3], ZnS:Ni[3], etc. (Fig. 1). As an example, the photoelectrode system demonstrated formate generation with a solar-to-chemical conversion efficiency of 4.6 % by a non-biased tablet-formed device immersed in an aqueous solution [4].One recent topic is a visible-light-driven Z-schematic CO2 reduction using H2O as an electron donor in aqueous particulate suspension system which can be operated in a simple mixture of [Ru(4,4’-diphosphonate-2,2’-bipyridine)(CO)2Cl2] ([Ru(dpbpy)] modified (CuGa)1-xZn2xS2 (CGZS) hybrid photocatalyst as a CO2 reduction, BiVO4 photocatalyst as a water oxidation and Co-complex as an electron mediator [5]. The CO2 reduction activity was significantly dependent on the composition of CGZS, and utilization of [Ru(dpbpy)]/CGZS at x=0.7 (E g = 2.36 eV) showed the highest Z-schematic CO2 reduction activity for CO and HCOO- production accompanying O2 generation under visible-light irradiation. The very high CO2 reduction selectivity beyond 60% under visible light irradiation as the aqueous particulate suspension suggests that particulate Z-schematic system is feasible to construct selective and efficient photocatalytic system for CO2 fixation and solar fuel generation. An electrode system using earth-abundant elements such as Mn[6], Fe[7] and Si will also be presented.[8]- References[1] S. Sato, T. Morikawa, et al, Angew. Chem. Int. Ed. 2010, 49, 5101-5105.[2] S. Sato, T. Arai, T. Morikawa, et al., J. Am. Chem. Soc., 2011, 133, 15240-15243.[3] T. M. Suzuki, A. Kudo, T. Morikawa, Applied Catalysis B: Environ. 2018 , 224, 572–578.[4] T. Arai, S. Sato, T. Morikawa, Energy Environ. Sci., 201 5 , 8 , 1998-2002.[5] T. M. Suzuki, A. Kudo, T. Morikawa, et al., Chem. Commun., 2018, 54, 10199-10202[6] S. Sato, K.Sekizawa, et al, ACS Catal., 2018, 8, 4452-4458.[7] T. M. Suzuki, et al., Bull. Chem. Soc. Jpn, 2018, 91, 778–786.[8] T. Arai, et al., Chem. Commun., 2019, 55,237-240._ Figure 1