Increasing visible light absorption of classic wide-bandgap photocatalysts like TiO has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible-light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail-like absorption band in hydrogen-free oxygen-deficient TiO, an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO by intentionally introducing atomic hydrogen-mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo-electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide-bandgap semiconductors to fully capture solar light.
Yang Yongqiang Lichang Yin Gong Yue Ping Niu Jianqiang Wang Gu Lin 陈星秋 刘刚 王连洲 成会明
Although doping with appropriate heteroatoms is a powerful way of increasing visible light absorption of wide-bandgap metal oxide photocatalysts, the incorporation of heteroatoms into the photocatalysts usually leads to the increase of deleterious recombination centers of photogenerated charge carriers. Here, a conceptual strategy of increasing visible light absorption without causing additional recombination centers by constructing an ultrathin insulating heterolayer of amorphous boron oxynitride on wide-bandgap photocatalysts is shown. The nature of this strategy is that the active composition nitrogen in the heterolayer can noninvasively modify the electronic structure of metal oxides for visible light absorption through the interface contact between the heterolayer and metal oxides. The photocatalysts developed show significant improvements in photocatalytic activity under both UV–vis and visible light irradiation compared to the doped counterparts by conventional doping process. These results may provide opportunities for flexibly tailoring the electronic structure of metal oxides.
Yu Zong Bao 陈星秋 Xiangdong Kang Yingpeng Xie Zhu Huaze Wang Shoulong Ullah Sami Ma Hui 王连洲 刘刚 Xiuliang Ma 成会明
Anatase TiO 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 TiO 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.
Hong Xingxing Kang Yuyang Zhen Chao Xiangdong Kang Lichang Yin Irvine John T.S. 王连洲 刘刚 成会明
Science China Materials
Extending visible light absorption range and suppressing the recombination of photogenerated charge carriers are always important topics in developing efficient solar-driven photocatalysts. In this study, the thermal treatment process at 400 °C in a high-pressure hydrogen atmosphere was applied to modify graphitic carbon nitride. Compared to the normal atmospheric hydrogen treatment process, this process has the merit of producing nitrogen deficient graphitic carbon nitride in high-yield. The optimal photocatalytic activity of modified graphitic carbon nitride was demonstrated by controlling the treatment duration in the hydrogen atmosphere. The changes in the crystal structure, microstructure and optical properties of carbon nitrides were investigated by several characterizations. The relationship between the photocatalytic activity and structures of graphitic carbon nitride was preliminarily established. The results obtained in this study could provide some new ways of improving the activity of graphitic carbon nitride based photocatalyst.
Xiangdong Kang Kang Yuyang Hong Xingxing Zhenhua Sun Zhen Chao Hu Chao-Hao 刘刚 成会明
Progress in Natural Science: Materials International
Photocatalytic water oxidation for O evolution is known as a bottle neck in water splitting. Various strategies have been conducted to keep the energetics of photogenerated holes or to create more holes in the bulk to reach the surface for efficient photocatalytic water oxidation. Our previous study demonstrated the effectiveness of interstitial boron doping in improving photocatalytic water oxidation by lowering the valence band maximum of TiO with a concentration gradient of boron. In this study, homogeneous doping of interstitial boron was realized in a TiO shell with mixed anatase/rutile phases that was produced by the gaseous hydrolysis of the surface layer of TiB crystals in a moist argon atmosphere. Consequently, the homogeneous doping and lowered valence band maximum improved the energetics of holes for efficient photocatalytic water oxidation.
Yang Yongqiang Kang Yuyang 刘刚 成会明
Chinese Journal of Catalysis
The efficiency of perovskite solar cells (PSCs) has increased from around 4% to over 22% following a few years of intensive investigation. For most PSCs, organic materials such as 2,2′,7,7′-tetrakis(N,N-pdimethoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) are used as the hole transporting materials (HTMs), which are thermally and chemically unstable and also expensive. Here, we explored nickel phthalocyanine (NiPc) as a stable and cost-effective HTM to replace the conventionally used spiro-OMeTAD. Because of its high carrier mobility and proper band alignments, we achieved a PCE of 12.1% on NiPc based planar device with short-circuit current density (J) of 17.64 mA cm, open circuit voltage (V) of 0.94 V, and fill factor (FF) of 73%, outperforming the planar device based on copper phthalocyanine (CuPc) that is an outstanding representative of metal phthalocyanines (MPcs) reported. Moreover, the device with NiPc shows much improved stability compared to that based on the conventional spiro-OMeTAD as a result of NiPc's high stability. Photoluminescence (PL) and Impedance spectroscopy analysis results show that thermally deposited NiPc has good hole-extraction ability. Our results suggest that NiPc is a promising HTM for the large area, low cost and stable PSCs.
Haider Mustafa Zhen Chao Wu Ting-Ting 刘刚 成会明
Journal of Materials Science and Technology
Integrating a semiconducting light absorber with an appropriate co-catalyst appears almost indispensable for photocatalytic solar fuel generation. Although ferroelectric materials with spontaneous electrical polarization are considered promising light absorbers with the ability to induce oppositely directed transport of photogenerated electrons and holes in the bulk, their applications are intrinsically restricted by the large Schottky barrier at the interface of the ferroelectric material and the co-catalyst, which has a larger work function. Here, we demonstrate that, by selective chemical epitaxial growth of anatase TiO islands on the positively poled (00-1) facet of PbTiO single-crystal particles to form an atomically smooth interface with a small potential difference, the material shows significantly improved photocatalytic hydrogen and oxygen generation under both UV-visible and visible light, while the island-free PbTiO is inactive in visible light. This strategy may be applicable to various ferroelectric materials to produce unusual asymmetric micro-nano structures for excellent performance. Photocatalysis is intrinsically dependent on the synergy of three distinct steps, namely, light absorption, separation and transfer of photogenerated charge carriers, and surface catalysis. Ferroelectric materials such as tetragonal PbTiO with a spontaneous polar field as light absorbers have unique directional transport of photogenerated electrons and holes in the bulk along the ferroelectric field so that the electrons and holes can reach different surfaces. Prior to inducing a catalytic reaction, the effective transfer of charge carriers from the ferroelectric photocatalyst to a suitable co-catalyst such as Pt is indispensable but usually limited by the large Schottky barrier between them. In this study, the selective epitaxial growth of anatase TiO nano-islands on the positively poled (001¯) facet of PbTiO is demonstrated to be effective in fully addressing such a limitation and greatly improving the photocatalytic activity of ferroelectric photocatalysts. Selective chemical epitaxial growth of anatase TiO islands on the positively poled (001¯) facet of the ferroelectric PbTiO photocatalyst can significantly boost photocatalytic hydrogen and oxygen generation under both UV-visible light and visible light largely as a result of the greatly lowered Schottky barrier between PbTiO and co-catalyst Pt, promoting the charge transfer process between them. This strategy might be applied to modify various ferroelectric photocatalysts to produce unusual asymmetric micro-nano structures for excellent performance.
刘刚 Ma Li Lichang Yin Wan Gedeng Zhu Huaze Zhen Chao Yang Yongqiang Liang Yan Tan Jun 成会明
Changing the composition and/or structure of some metal oxides at the atomic level can significantly improve their performance in different applications. Although many strategies have been developed, the introduction of heteroatoms, particularly anions to the internal part of metal oxide particles, is still not adequate. Here, an effective strategy is demonstrated for directly preparing polycrystalline decahedral plates of substitutional carbon-doped anatase TiO from titanium (IV) oxalate by a thermally induced topotactic transition in an inert atmosphere. Because of the carbon concentration gradient introduced in side of the plates, the carbon-doped TiO (TiO C) shows an increased visible light absorption and a two orders of magnitude higher electrical conductivity than pure TiO. Consequently, it can be used as a photocatalyst and an active material for lithium storage and shows much superior activity in generating hydroxyl radicals under visible light and greatly increased electrical-specific capacity at high charge–discharge rates. The strategy developed could also be applicable to the atomic-scale modification of other metal oxides.
Ping Niu Wu Ting-Ting Wen Lei Tan Jun Yang Yongqiang Shijian Zheng Liang Yan Li Feng Irvine John T.S. 刘刚 Xiuliang Ma 成会明
Lithium-sulfur batteries have attracted much attention because of their high theoretical energy density and cost effectiveness. However, severe polysulfide dissolution in organic electrolytes causes low sulfur utilization, fast capacity decay and poor coulombic efficiency. Here, we report a conductive polar MoC@MoOmaterial for efficient polysulfide immobilization and conversion during redox reactions. The polar MoOshell enables the chemical adsorption of polysulfides, and the conductive MoC core facilitates the conversion of polysulfides to LiS. The incorporation of the MoC@MoOmaterial in a carbon fiber foam electrode results in significantly improved electrochemical performance with a high specific capacity and good cycling stability. Our approach is a proof-of-concept study of the effective role of conductive polar materials in improving the redox chemistry of Li-S batteries.
Ruopian Fang Zhao Shi-Yong Zhenhua Sun Dawei Wang Rose Amal Shaogang Wang 成会明 Li Feng
Energy Storage Materials
Lithium-sulfur (Li-S) batteries are promising electrochemical energy storage systems because of their high theoretical energy density, natural abundance, and environmental benignity. However, several problems such as the insulating nature of sulfur, high solubility of polysulfides, large volume variation of the sulfur cathode, and safety concerns regarding the lithium anode hinder the commercialization of Li-S batteries. Graphene-based materials, with advantages such as high conductivity and good flexibility, have shown effectiveness in realizing Li-S batteries with high energy density and high stability. These materials can be used as the cathode matrix, separator coating layer, and anode protection layer. In this review, the recent progress of graphene-based materials used in Li-S batteries, including graphene, functionalized graphene, heteroatom-doped graphene, and graphene-based composites, has been summarized. And perspectives regarding the development trend of graphene-based materials for Li-S batteries have been discussed.
Chen Ke Zhenhua Sun Ruopian Fang Li Feng 成会明
Wuli Huaxue Xuebao/ Acta Physico - Chimica Sinica