CO2-to-CO conversion with over 10% efficiency using earth abundant system in a single-compartment reactor with oxygen tolerant Mn complex catalyst.

The direct conversion of CO2 in flue gas to value-added chemicals is a potentially important cost-effective solar-driven CO2 reduction technology. The present work demonstrates the solar-powered conversion of CO2 to CO with greater than 10% efficiency using a Mn complex cathode and an Fe-Ni anode in a single-compartment reactor without an ion exchange membrane in conjunction with a Si solar cell. Reactors separated by ion exchange membranes are typically used to prevent any effects of oxygen generated by the counter electrode.

Photocatalytic CO Reduction Using an Osmium Complex as a Panchromatic Self-Photosensitized Catalyst: Utilization of Blue, Green, and Red Light.

The photocatalytic reduction of carbon dioxide (CO) represents an attractive approach for solar-energy storage and leads to the production of renewable fuels and valuable chemicals. Although some osmium (Os) photosensitizers absorb long wavelengths in the visible-light region, a self-photosensitized, mononuclear Os catalyst for red-light-driven CO reduction has not yet been exploited. Here, we discovered that the introduction of an Os metal to a PNNP-type tetradentate ligand resulted in the absorption of light with longer-wavelength (350-700 nm) and that can be applied to a panchromatic self-photosensitized catalyst for CO reduction to give mainly carbon monoxide (CO) with a total turnover number (TON) of 625 under photoirradiation (λ≥400 nm).

Enhanced performance of molecular electrocatalysts for CO reduction in a flow cell following K addition.

Electrocatalytic CO reduction is a key aspect of artificial photosynthesis systems designed to produce fuels. Although some molecular catalysts have good performance for CO reduction, these compounds also suffer from poor durability and energy efficiency. The present work demonstrates the improved CO reduction activity exhibited by molecular catalysts in a flow cell.

Importance of steric bulkiness of iridium photocatalysts with PNNP tetradentate ligands for CO reduction.

A series of Ir complexes has been developed as multifunctional photocatalysts for CO reduction to give HCOH selectively. The catalytic activities and photophysical properties vary widely across the series, and the bulky group insertion resulted in the formation of HCOH and CO with the catalyst turnover number of >10 400.

Solar-Driven CO Reduction Using a Semiconductor/Molecule Hybrid Photosystem: From Photocatalysts to a Monolithic Artificial Leaf.

The synthesis of organic chemicals from HO and CO using solar energy is important for recycling CO through cyclical use of chemical ingredients produced from CO or molecular energy carriers based on CO. Similar to photosynthesis in plants, the CO molecules are reduced by electrons and protons, which are extracted from HO molecules, to produce O. This reaction is uphill; therefore, the solar energy is stored as the chemical bonding energy in the organic molecules.

Study of Excited States and Electron Transfer of Semiconductor-Metal-Complex Hybrid Photocatalysts for CO Reduction by Using Picosecond Time-Resolved Spectroscopies.

A semiconductor-metal-complex hybrid photocatalyst was previously reported for CO reduction; this photocatalyst is composed of nitrogen-doped Ta O as a semiconductor photosensitizer and a Ru complex as a CO reduction catalyst, operating under visible light (>400 nm), with high selectivity for HCOOH formation of more than 75 %. The electron transfer from a photoactive semiconductor to the metal-complex catalyst is a key process for photocatalytic CO reduction with hybrid photocatalysts. Herein, the excited-state dynamics of several hybrid photocatalysts are described by using time-resolved emission and infrared absorption spectroscopies to understand the mechanism of electron transfer from a semiconductor to the metal-complex catalyst.

Photocatalytic CO Reduction Using a Robust Multifunctional Iridium Complex toward the Selective Formation of Formic Acid.

A highly efficient tetradentate PNNP-type Ir photocatalyst, Mes-IrPCY2, was developed for the reduction of carbon dioxide. The photocatalyst furnished formic acid (HCOH) with 87% selectivity together with carbon monoxide to achieve a turnover number of 2560, which is the highest among CO reduction photocatalysts without an additional photosensitizer. Mes-IrPCY2 exhibited outstanding photocatalytic CO reduction activity in the presence of the sacrificial electron source 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[]imidazole (BIH) in CO-saturated ,-dimethylacetamide under irradiation with visible light.

Photoelectrochemical water-splitting over a surface modified p-type CrO photocathode.

Cr2O3 is a p-type semiconductor with a negative conduction band minimum position suitable for photocathodic H2 generation. Therefore, Cr2O3 is a candidate photocathode material for photoelectrochemical (PEC) water-splitting. However, Cr2O3 has not yet been applied for the purpose of H2 generation because the efficiency and stability of the photocurrent generated by a Cr2O3 electrode are poor, due to high defect and vacancy concentrations.

Molecular Catalysts Immobilized on Semiconductor Photosensitizers for Proton Reduction toward Visible-Light-Driven Overall Water Splitting.

Photocatalytic or photoelectrochemical hydrogen production by water splitting is one of the key reactions for the development of an energy supply that enables a clean energy system for a future sustainable society. Utilization of solar photon energy for the uphill water splitting reaction is a promising technology, and therefore many systems using semiconductor photocatalysts and semiconductor photoelectrodes for the reaction producing hydrogen and dioxygen in a 2:1 stoichiometric ratio have been reported. In these systems, molecular catalysts are also considered to be feasible; recently, systems based on molecular catalysts conjugated with semiconductor photosensitizers have been used for photoinduced hydrogen generation by proton reduction.

Solar-driven CO to CO reduction utilizing HO as an electron donor by earth-abundant Mn-bipyridine complex and Ni-modified Fe-oxyhydroxide catalysts activated in a single-compartment reactor.

Photoelectrochemical CO2 to CO reduction was demonstrated with 3.4% solar-to-chemical conversion efficiency using polycrystalline silicon photovoltaic cells connected with earth-abundant catalysts: a manganese complex polymer for CO2 reduction and iron oxyhydroxide modified with a nickel compound for water oxidation. The system operated around neutral pH in a single-compartment reactor.

Band bending and dipole effect at interface of metal-nanoparticles and TiO directly observed by angular-resolved hard X-ray photoemission spectroscopy.

This paper describes the observation of band bending and band edge shifts at the interfaces between nanoscale metals and TiO2 film over a wide depth range by angular-resolved hard X-ray photoemission spectroscopy (HAXPES). The HAXPES results indicate strong electrostatic interactions between the TiO2 semiconductor and metal nanoparticles, while density functional theory (DFT) calculations suggest that these interactions are primarily associated with charge transfer leading to electric dipole moments at the interface in the ground state. The effects of these dipole moments are not limited to the surface but also occur deep in the bulk of the semiconductor, and are highly dependent on the coverage of the metal nanoparticles on the semiconductor species.

Visible-light-driven CO reduction on a hybrid photocatalyst consisting of a Ru(ii) binuclear complex and a Ag-loaded TaON in aqueous solutions.

A hybrid photocatalyst consisting of a Ru(ii) binuclear complex and a Ag-loaded TaON reduced CO by visible light even in aqueous solution. The distribution of the reduction products was strongly affected by the pH of the reaction solution. HCOOH was selectively produced in neutral conditions, whereas the formation of HCOOH competed with H evolution in acidic conditions.

Selective Formic Acid Production via CO2 Reduction with Visible Light Using a Hybrid of a Perovskite Tantalum Oxynitride and a Binuclear Ruthenium(II) Complex.

A hybrid material consisting of CaTaO2N (a perovskite oxynitride semiconductor having a band gap of 2.5 eV) and a binuclear Ru(II) complex photocatalytically produced HCOOH via CO2 reduction with high selectivity (>99%) under visible light (λ>400 nm). Results of photocatalytic reactions, spectroscopic measurements, and electron microscopy observations indicated that the reaction was driven according to a two-step photoexcitation of CaTaO2N and the Ru photosensitizer unit, where Ag nanoparticles loaded on CaTaO2N with optimal distribution mediated interfacial electron transfer due to reductive quenching.

Visible-light-driven CO2 reduction with carbon nitride: enhancing the activity of ruthenium catalysts.

A heterogeneous photocatalyst system that consists of a ruthenium complex and carbon nitride (C3N4), which act as the catalytic and light-harvesting units, respectively, was developed for the reduction of CO2 into formic acid. Promoting the injection of electrons from C3N4 into the ruthenium unit as well as strengthening the electronic interactions between the two units enhanced its activity. The use of a suitable solvent further improved the performance, resulting in a turnover number of greater than 1000 and an apparent quantum yield of 5.

Structural improvement of CaFe₂O₄ by metal doping toward enhanced cathodic photocurrent.

Various metal-doped p-type CaFe2O4 photocathodes were prepared in an attempt to improve the low quantum efficiency for photoreaction. CuO and Au doping enhanced the photocurrent by expansion of the absorption wavelength region and plasmon resonance, respectively. X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analysis showed that doping with these metals further disturbed the originally distorted crystal structure of CaFe2O4.

Hybridization between periodic mesoporous organosilica and a Ru(II) polypyridyl complex with phosphonic acid anchor groups.

A new method for the hybridization of a ruthenium(II) polypyridyl complex ([Ru(bpy)2((CH2PO3H2)2-bpy)](2+) (RuP2(2+): bpy =2,2'-bipyridine; (CH2PO3H2)2-bpy =2,2'-bipyridine-4,4'di(metylphosphonic acid)) with biphenylene-bearing periodic mesoporous organosilica (Bp-PMO made from 4,4'bis(triethoxysilyl)biphenyl [(C2H5O)3Si-(C6H4)2-Si(OC2H5)3]) was developed. Efficient and secure fixation of the ruthenium(II) complex with methylphosphonic acid groups (RuP2(2+)) in the mesopores of Bp-PMO occurred. This method introduced up to 660 μmol of RuP2(2+) in 1 g of Bp-PMO.

A polymeric-semiconductor-metal-complex hybrid photocatalyst for visible-light CO(2) reduction.

A polymeric carbon nitride semiconductor is demonstrated to photocatalyse CO2 reduction to formic acid under visible light (λ > 400 nm) with a high turnover number (>200 for 20 hours) and selectivity (>80%), when coupled with a molecular ruthenium complex as a catalyst.

Artificial Z-scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO2.

A hybrid for the visible-light-driven photocatalytic reduction of CO2 using methanol as a reducing agent was developed by combining two different types of photocatalysts: a Ru(II) dinuclear complex (RuBLRu') used for CO2 reduction is adsorbed onto Ag-loaded TaON (Ag/TaON) for methanol oxidation. Isotope experiments clearly showed that this hybrid photocatalyst mainly produced HCOOH (TN = 41 for 9 h irradiation) from CO2 and HCHO from methanol. Therefore, it converted light energy into chemical energy (ΔG° = +83.

Photocatalytic reduction of CO₂: from molecules to semiconductors.

We are facing three serious problems related to fossil resources, i.e., shortage of energy, shortage of carbon resources, and the global worming problem.