Ge Yin

Photocatalytic carbon dioxide reduction by copper oxide nanocluster-grafted niobate nanosheets.

Amorphous copper oxide (Cu(II)) nanoclusters function as efficient electrocatalysts for the reduction of carbon dioxide (CO2) to carbon monoxide (CO). In addition to promoting electrocatalytic activity, Cu(II) nanoclusters act as efficient cocatalyts for CO2 photoreduction when grafted onto the surface of a semiconductor (light harvester), such as niobate (Nb3O8(-)) nanosheets. Here, the photocatalytic activity and reaction pathway of Cu(II)-grafted Nb3O8(-) nanosheets was investigated using electron spin resonance (ESR) analysis and isotope-labeled molecules (H2(18)O and (13)CO2). The results of the labeling experiments demonstrated that under UV irradiation, electrons are extracted from water to produce oxygen ((18)O2) and then reduce CO2 to produce (13)CO. ESR analysis confirmed that excited holes in the valence band of Nb3O8(-) nanosheets react with water, and that excited electrons in the conduction band of Nb3O8(-) nanosheets are injected into the Cu(II) nanoclusters through the interface and are involved in the reduction of CO2 into CO. The Cu(II) nanocluster-grafted Nb3O8(-) nanosheets are composed of nontoxic and abundant elements and can be facilely synthesized by a wet chemical method. The nanocluster grafting technique described here can be applied for the surface activation of various semiconductor light harvesters, such as metal oxide and/or metal chalcogenides, and is expected to aid in the development of efficient CO2 photoreduction systems.

Selective electro- or photo-reduction of carbon dioxide to formic acid using a Cu–Zn alloy catalyst

A copper-and-zinc (Cu–Zn) alloy material was synthesized using a vacuum sealing method, in which evaporated zinc was reacted with copper film or nanoparticles to form a homogeneous Cu–Zn alloy. This alloy was evaluated as an electrocatalyst and/or cocatalyst for photocatalysis to selectively reduce carbon dioxide to formic acid. Based on the optimised alloy composition, the Cu5Zn8 catalyst exhibited efficient electrochemical CO2 reduction. Furthermore, we constructed a photoelectrochemical (PEC) three-electrode system, in which the Cu5Zn8 film functioned as the cathode for CO2 reduction in the dark and strontium titanate (SrTiO3) served as the photoanode for water oxidation. The PEC system also selectively reduced CO2 to formic acid with a faradaic efficiency of 79.11% under UV-light and the absence of an applied bias potential. SrTiO3 particles decorated with nanoparticles of the Cu–Zn alloy also photocatalytically reduced CO2 to formic acid under UV-light. Isotope trace analysis demonstrated that water served as the electron donor to produce oxygen and organic molecules under UV light, similar to photosynthesis in plants. The Cu–Zn alloy material developed in the present study is composed of ubiquitous and safe materials, and can catalyse CO2 conversion by means of various kinds of renewable energies.

Examination of interfacial charge transfer in photocatalysis using patterned CuO thin film deposited on TiO2

We examined the interfacial charge transfer effect on photocatalysts using a patterned CuO thin film deposited on a rutile TiO2 (110) substrate. Photocatalytic activity was visualized based on the formation of metal Ag particles resulting from the photoreduction of Ag+ ions under visible-light illumination. Ag particles were selectively deposited near the edge of CuO film for several nanometer thick CuO film, indicating that interfacial excitation from the valence band maximum of TiO2 to the conduction band minimum of CuO plays a key role in efficient photocatalytic activity of CuO nanocluster-grafted TiO2 systems with visible-light sensitivity.

Direct Observation of Interfacial Charge Transfer between Rutile TiO2 and Ultrathin CuOx Film by Visible-Light Illumination and Its Application for Efficient Photocatalysis

A well‐defined interface between CuOx film and TiO2 is constructed as a model for elucidating the interfacial charge transfer (IFCT) process that occurs during photocatalysis. Spectroscopic analysis revealed strong blue light absorption at 2.7 eV in this film system. Based on photoemission spectroscopy and the UV‐visible absorption analysis, the band offset of CuOx and TiO2 was investigated, and the observed blue absorption at 2.7 eV could be explained by an IFCT process, in which electrons in the valence band of TiO2 were excited into the conduction band of the ultrathin CuOx film. Furthermore, the IFCT transition was found to strongly depend on the crystal face of TiO2, as the IFCT absorption was significantly increased in the ultrathin CuOx film coated over the rutile TiO2 (110) substrate. Probe reduction and oxidation reactions were also used to investigate the charge transport process and determine photocatalytic reaction sites, which were located around a few nanometers‐scale region from the edge of the ultrathin CuOx and TiO2. The present findings provide a powerful method for the development of efficient visible‐light sensitive photocatalysts based on the IFCT concept.