Chao Zhen

A red anatase TiO2 photocatalyst for solar energy conversion

Narrowing the bandgap of wide-bandgap semiconductor photocatalysts (for instance, anatase TiO2) by introducing suitable heteroatoms has been actively pursued for increasing solar absorption, but usually suffers from a limited thermodynamic/kinetic solubility of substitutional dopants in bulk and/or dopant-induced recombination centres. Here we report a red anatase TiO2 microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach for harvesting the full spectrum of visible light. This approach uses a pre-doped interstitial boron gradient to weaken nearby Ti-O bonds for the easy substitution of oxygen by nitrogen, and consequently it substantially improves the nitrogen solubility. Furthermore, no nitrogen-related Ti3+ was formed in the red TiO2 due to a charge compensation effect by boron, which inevitably occurs in common nitrogen doped TiO2. The red anatase TiO2 exhibits photoelectrochemical water splitting activity under visible light irradiation. The results obtained may shed light on how to increase high visible light absorbance of wide-bandgap photocatalysts.

Template-free synthesis of Ta3N5 nanorod arrays for efficient photoelectrochemical water splitting

We report the template-free synthesis of Ta3N5 nanorod array films grown on Ta foil by a combination of a vapor-phase hydrothermal process and subsequent nitriding. The Ta3N5 nanorod array film modified with Co(OH)x when used as a photoanode in a photoelectrochemical cell for water splitting yields a stable photocurrent density of 2.8 mA cm(-2) at 1.23 VRHE under AM 1.5G simulated sunlight. The incident photon-to-current conversion efficiency at 480 nm is determined to be 37.8%.

Tantalum (oxy)nitride based photoanodes for solar-driven water oxidation

Photoelectrochemical (PEC) water splitting is a very promising process to produce hydrogen as a clean energy carrier. To achieve 10% solar to hydrogen (STH) conversion efficiency required for practical applications, the current central task in PEC water splitting is the development of efficient photoelectrodes, particularly photoanodes for water oxidation, used in PEC cells. Tantalum (oxy)nitrides with bandgaps ranging from 2.5 to 1.9 eV, corresponding to theoretical STH efficiencies varying from 9.3% to 20.9%, are considered a class of attractive light adsorbers for use in photoanodes for PEC water oxidation and have attracted much recent research attention. In this review, the recent development of tantalum (oxy)nitride photoanodes is summarized. Special interest is focused on the synthesis methods of tantalum (oxy)nitride films and important approaches for improving PEC conversion efficiency and stability of these films as photoanodes. The future trends of tantalum (oxy)nitride based photoanodes are also discussed.

Nonstoichiometric rutile TiO2 photoelectrodes for improved photoelectrochemical water splitting

A new type of nonstoichiometric rutile titanium dioxide (TiO2) film with around 15 at% oxygen vacancies homogeneously distributed throughout the bulk was prepared. The resultant films, when used as a photoelectrode, showed a photoelectrochemical water splitting activity 1.7 times that of stoichiometric TiO2 at a bias of 0.9 V vs. Ag/AgCl. This is believed to result from the synergistic effect of the improved bulk transport and surface transfer of charge carriers compared to the stoichiometric rutile TiO2.

Greatly Enhanced Electronic Conduction and Lithium Storage of Faceted TiO2 Crystals Supported on Metallic Substrates by Tuning Crystallographic Orientation of TiO2

Electronic conduction along the [001] direction of a faceted anatase TiO2 particle in contact with two tungsten probes is found to be an order of magnitude higher than that along the [010] direction due to a smaller potential barrier of the TiO2 (001)-tungsten interface for electron transport than the TiO2 (010)-tungsten interface. This finding could guide the design of TiO2 -based electrodes.

Synthesis of mesoporous single crystal rutile TiO2 with improved photocatalytic and photoelectrochemical activities

Mesoporous single crystal rutile TiO2 with clear facets was prepared by a seeded template method. As a result of unique microstructure, the resulting TiO2 exhibits remarkably improved photocatalytic and photoelectrochemical activities in hydrogen or oxygen evolution.

A film of rutile TiO2 pillars with well-developed facets on an α-Ti substrate as a photoelectrode for improved water splitting

A photoelectrode of single-crystal rutile TiO(2) pillars with well-developed facets shows a 2.5 times higher capability of water splitting at 0.3 V than a conventional anatase TiO(2) nanotube array electrode. The improvement is attributed to the synergistic effects of the high crystallinity of single-crystal rutile pillars, the exposed high-energy {011} and {111} as the reactive facets of water oxidation reaction and the extended light absorption range by ca. 23 nm.

Design and construction of a film of mesoporous single-crystal rutile TiO2 rod arrays for photoelectrochemical water oxidation

A film of mesoporous single-crystal rutile TiO2 rod arrays supported on a transparent conductive glass substrate was synthesized with the assistance of a template layer of closely packed silica nanospheres. This film was used as a photoanode and showed significant improvement for photoelectrochemical water oxidation compared with a reference film of nonporous single-crystal rutile TiO2 rod arrays.

Maximizing the visible light photoelectrochemical activity of B/N-doped anatase TiO2 microspheres with exposed dominant {001} facets

Anatase TiO2 microspheres with exposed dominant BBBBB001BBBBB facets were doped with interstitial boron to have a concentration gradient with the maximum concentration at the surface. They were then further doped with substitutional nitrogen by heating in an ammonia atmosphere at different temperatures from 440 to 560°C to give surface N concentrations ranging from 7.03 to 15.47 at%. The optical absorption, atomic and electronic structures and visible-light photoelectrochemical water oxidation activity of these materials were investigated. The maximum activity of the doped TiO2 was achieved at a nitrogen doping temperature of 520°C that gave a high absorbance over the whole visible light region but with no defect-related background absorption.摘要本文以锐钛矿TiO2微米球光催化材料为研究对象, 其表面主要由BBBBB001BBBBB晶面组成, 间隙掺杂硼原子在微米球中呈浓度梯度分布, 浓度 最高点位于表面. 通过对其在氨气气氛、不同温度下(440–560°C)进行热处理, 可实现氮替代晶格氧的掺杂, 氮原子掺杂的浓度随着热处理 温度的增加, 由7.03增加到15.47 at%. 随着掺杂氮浓度的增加, 所得掺杂TiO2微米球的可见光吸收强度相应提高. 进一步研究所得掺杂TiO2 微米球的可见光光吸收、原子和电子结构与可见光光电催化水氧化活性的关联特性, 发现在520°C下所得氮掺杂TiO2的可见光光电催化 水氧化活性最大, 该样品吸收光谱的显著特征是在可见光区吸光率高, 且没有与缺陷相关联的背底吸收.