Artificial photosynthesis by light absorption, charge separation, and multielectron catalysis

Abstract

Our society's current energy demands are largely met by the exploitation of fossil fuels, which are unsustainable and environmentally harmful resources. However, Nature has provided us with a clean and virtually limitless alternative in the form of solar energy. This abundant resource is utilized constantly by photosynthetic organisms, which has in turn motivated decades of research in our quest to create artificial counterparts of comparable scales. In this feature article, we will highlight some of the recent novel approaches in the field of artificial photosynthesis (AP), which we define by a more general term as a process that stores energy overall by generating fuels and chemicals using light. We will particularly emphasize on the potential of a highly modular plug-and-play concept that we hope will persuade the community to explore a more inclusive variety of multielectron redox catalysis to complement the proton reduction and water oxidation half-reactions in traditional solar water splitting systems. We discuss some of the latest developments in the vital functions of light harvesting, charge separation, and multielectron reductive and oxidative catalysis, as well as their optimization, to achieve the ultimate goal of storing sunlight in chemical bonds. Specific attention is dedicated to the use of earth-abundant elements and molecular catalysts that offer greater product selectivity and more intricate control over the reactivity than heterogeneous systems. In this context, we showcase our team's contributions in presenting a unique oxidative carbon-carbon bond cleavage reaction in aliphatic alcohols and biomass model compounds, under ambient atmospheric conditions, facilitated by vanadium photocatalysts. We offer this discovery as a promising alternative to water oxidation in an integrated AP system, which would concurrently generate both solar fuels and valuable solar chemicals.

Completely Solvent-free Protocols to Access Phase-Pure, Metastable Metal Halide Perovskites and Functional Photodetectors from the Precursor Salts

“…As part of the sustainable energy and green chemistry efforts in our team, we have recently been developing multi-dimensional lead and tin halide perovskites for light absorption and emission purposes (Koh et al., 2016, Thirumal et al., 2017) and creating innovative energy solutions based on artificial photosynthesis (Dokic and Soo, 2018, Gazi et al., 2017, Hong et al., 2019, Lim et al., 2018, Ng et al., 2018). Simultaneously, we have also been developing more eco-friendly, essentially solvent-free, mechanochemical approaches for the synthesis, functionalization, and transformation of main group compounds (Shi et al., 2016, Sim et al., 2017, Sim et al., 2018) and complexes (Geciauskaite and Garcia, 2017, Tan and Garcia, 2019, Wang et al., 2016, Wang et al., 2017).…”

Mesoporous SiO2/BiVO4/CuO nanospheres for Z-scheme, visible light aerobic C–N coupling and dehydrogenation

“…The exploitation of solar energy in the production of fuels and chemicals has taken on greater urgency lately due to the increasingly palpable environmental and economic effects of global climate change. To address this challenge, several groups, including ours [1][2][3][4][5][6][7][8][9]. have been inspired by the effectiveness of natural photosynthesis in capturing sunlight and coupling the separated charges for multielectron redox catalysis.…”

“…The two chromophores, chlorophylls P680 and P700, are organized so that electrons flow from P680 to P700 with high fidelity by interfacing with both thermodynamically and kinetically favorable intermediates. This essentially creates a "molecular photodiode" for effective light absorption and charge separation, allowing P680 to build up four holes to oxidize water, while P700 acquires two electrons to reduce NADP + [9].…”

“…Z. Li and his co-workers have also used metal organic frameworks (MOFs) [37,38] and ZnIn 2 S 4 [39] in the oxidation of amines to imines, which are important building blocks for the synthesis of fine chemicals. In the same vein, our team has been developing alternative approaches to harness sunlight in the production of solar chemicals and fuels, while using exclusively earth abundant elements [9]. We have developed molecular complexes and metal oxide semiconductors as chromophores [40,41], molecular Ni electrocatalysts capable of H 2 evolution from seawater [42], and molecular V photocatalysts that mediate C-C bond cleavage in biomass lignin model compounds, with the intention of integrating them into one unit for solar chemicals production [9,43,44].…”

“…In the same vein, our team has been developing alternative approaches to harness sunlight in the production of solar chemicals and fuels, while using exclusively earth abundant elements [9]. We have developed molecular complexes and metal oxide semiconductors as chromophores [40,41], molecular Ni electrocatalysts capable of H 2 evolution from seawater [42], and molecular V photocatalysts that mediate C-C bond cleavage in biomass lignin model compounds, with the intention of integrating them into one unit for solar chemicals production [9,43,44]. Some candidates that have emerged for solar to chemical energy conversion are Bi-based materials, due to their efficient photocatalytic performance, high stability, low cost, and modest toxicity [45].…”