Coupling carbon dioxide reduction with water oxidation in nanoscale photocatalytic assemblies

Abstract

The reduction of carbon dioxide by water with sunlight in an artificial system offers an opportunity for utilizing non-arable land for generating renewable transportation fuels to replace fossil resources. Because of the very large scale required for the impact on fuel consumption, the scalability of artificial photosystems is of key importance. Closing the photosynthetic cycle of carbon dioxide reduction and water oxidation on the nanoscale addresses major barriers for scalability as well as high efficiency, such as resistance losses inherent to ion transport over macroscale distances, loss of charge and other efficiency degrading processes, or excessive need for the balance of system components, to mention a few. For the conversion of carbon dioxide to six-electron or even more highly reduced liquid fuel products, introduction of a proton conducting, gas impermeable separation membrane is critical. This article reviews recent progress in the development of light absorber-catalyst assemblies for the reduction and oxidation half reactions with focus on well defined polynuclear structures, and on novel approaches for optimizing electron transfer among the molecular or nanoparticulate components. Studies by time-resolved optical and infrared spectroscopy for the understanding of charge transfer processes between the chromophore and the catalyst, and of the mechanism of water oxidation at metal oxide nanocatalysts through direct observation of surface reaction intermediates are discussed. All-inorganic polynuclear units for reducing carbon dioxide by water at the nanoscale are introduced, and progress towards core-shell nanotube assemblies for completing the photosynthetic cycle under membrane separation is described.

Synthesis of Large Surface‐Area g‐C3N4 Comodified with MnOx and Au‐TiO2 as Efficient Visible‐Light Photocatalysts for Fuel Production

“…[17] Compared to the widely investigated visiblelight photocatalysts containing metal, such as metal oxides, sulfides, and oxynitrides, a metal free polymeric graphitic carbon nitride (gC 3 N 4 ) as a prom ising photocatalyst has received great attention in the field of sustainable energy production for CO 2 conversion and H 2 evo lution, owing to its suitable energy bandgap (2.7 eV), high sta bility and unique surface properties. [17] Compared to the widely investigated visiblelight photocatalysts containing metal, such as metal oxides, sulfides, and oxynitrides, a metal free polymeric graphitic carbon nitride (gC 3 N 4 ) as a prom ising photocatalyst has received great attention in the field of sustainable energy production for CO 2 conversion and H 2 evo lution, owing to its suitable energy bandgap (2.7 eV), high sta bility and unique surface properties.…”

One‐Dimensional Earth‐Abundant Nanomaterials for Water‐Splitting Electrocatalysts

“…Hydrogen has been well recognized as one of the most abundant and promising candidates for clean energy supply to replace fossil fuels since the beginning of 1970's, as the only combustion product is water 6, 7, 8, 9, 10, 11, 12, 13. Although hydrogen is one of the most abundant elements in the world, free hydrogen molecules do not exist naturally.…”

“…The electrical water splitting represents ≈ 4% contribution of global hydrogen fuel production to date. Compared to other approaches, as the chemical reaction of water splitting is indeed the reverse reaction of hydrogen combustion, this process enables the complete and close cycle of hydrogen with zero carbon emission, and is thereby regarded as a substantially important and promising method 8, 9, 10, 11, 12, 13, 14…”

General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities

“…These limitations represent the key challenges in establishing the exact structure-to-property correlation in SACs, which is essential for the rational design and synthesis of new SACs with tailored activities for wide ranges of electrocatalytic processes [32][33][34] . Here, we report a general approach to a series of atomic 3d metals embedded in nitrogen-doped holey graphene frameworks (M-NHGFs, M = Fe, Co or Ni), unambiguously determining their atomistic structures and correlation with electrocatalytic activity towards the oxygen evolution reaction (OER); a reaction that is essential for diverse clean energy technologies including water splitting, CO 2 reduction and rechargeable metal-air batteries 2,[35][36][37] . Our studies show that different M-NHGFs adopt an identical MN 4 C 4 moiety with the same local atomic coordination configuration embedded in graphene lattices, as revealed by thorough analyses of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), and directly imaged by annular dark-field scanning transmission electron microscope (ADF-STEM).…”