Fuqiang Huang

Visible-light photocatalytic, solar thermal and photoelectrochemical properties of aluminium-reduced black titania

Utilizing solar energy for hydrogen generation and water cleaning is a great challenge due to insufficient visible-light power conversion. Here we report a mass production approach to synthesize black titania by aluminium reduction. The obtained sample possesses a unique crystalline core–amorphous shell structure (TiO2@TiO2−x). The black titania absorbs ∼65% of the total solar energy by improving visible and infrared absorption, superior to the recently reported ones (∼30%) and pristine TiO2 (∼5%). The unique core–shell structure (TiO2@TiO2−x) and high absorption boost the photocatalytic water cleaning and water splitting. The black titania is also an excellent photoelectrochemical electrode exhibiting a high solar-to-hydrogen efficiency (1.7%). A large photothermic effect may enable black titania “capture” solar energy for solar thermal collectors. The Al-reduced amorphous shell is proved to be an excellent candidate to absorb more solar light and receive more efficient photocatalysis.

Effective nonmetal incorporation in black titania with enhanced solar energy utilization

Nonmetal-doped black titania is achieved in a core–shell structure by a two-step synthesis. The nonmetal dopants in amorphous TiO2−x shells decrease e–h recombination centers, and more than 6.6 at.% N further improves solar energy absorption from 65% up to 85%. The photocatalytic H2 generation of the N-doped black titania is 15.0 mmol h−1 g−1 under 100 mW cm−2 of full-sunlight and 200 μmol h−1 g−1 under 90 mW cm−2 of visible-light irradiation, superior to TiO2−x and reported titania photocatalysis.

Direct PECVD growth of vertically erected graphene walls on dielectric substrates as excellent multifunctional electrodes

A novel uniform multi-level matrix of vertically erected graphene walls is directly grown on a dielectric substrate by plasma enhanced chemical vapor deposition (PECVD) at 900 °C without the presence of any catalyst and post-transfer treatment. Such a two-level structure is composed of continuous vertically erected graphene sheets (the second level) on a nanocrystalline graphene film (the first level). A nanocrystalline film is formed in the first stage (<15 min), and the graphene walls initialize on the boundary C sp3 atoms as nucleation centers to grow the erected graphene walls as the second-level component. The microstructure of the graphene walls can be modified by plasma power, growth time and seed layer coating. The unique three-dimensional graphene structure possessed high hydrophobicity (contact angle: 141°), outstanding electron conductivity (sheet resistance: 198 Ω sq−1), and tunable transparency (91.9–38.0% at 550 nm). The three-dimensional structure enables the graphene to act as an excellent electron transport network with high surface area in many aspects. The highly conductive graphene walls were used as the counter electrode of dye-sensitized solar cells (DSSC) with a photovoltaic efficiency of 6.01%, comparable to FTO-based DSSCs (6.10%). This in situ one-step growth indicates the great potential to fabricate excellent electrodes for photovoltaic and electronic applications.

Low-Temperature Aluminum Reduction of Graphene Oxide, Electrical Properties, Surface Wettability, and Energy Storage Applications

Low-temperature aluminum (Al) reduction is first introduced to reduce graphene oxide (GO) at 100-200 °C in a two-zone furnace. The melted Al metal exhibits an excellent deoxygen ability to produce well-crystallized reduced graphene oxide (RGO) papers with a low O/C ratio of 0.058 (Al-RGO), compared with 0.201 in the thermally reduced one (T-RGO). The Al-RGO papers possess outstanding mechanical flexibility and extremely high electrical conductivities (sheet resistance R(s) ~ 1.75 Ω/sq), compared with 20.12 Ω/sq of T-RGO. More interestingly, very nice hydrophobic nature (90.5°) was observed, significantly superior to the reported chemically or thermally reduced papers. These enhanced properties are attributed to the low oxygen content in the RGO papers. During the aluminum reduction, highly active H atoms from H(2)O reacted with melted Al promise an efficient oxygen removal. This method was also applicable to reduce graphene oxide foams, which were used in the GO/SA (stearic acid) composite as a highly thermally conductive reservoir to hold the phase change material for thermal energy storage. The Al-reduced RGO/SnS(2) composites were further used in an anode material of lithium ion batteries possessing a higher specific capacity. Overall, low-temperature Al reduction is an effective method to prepare highly conductive RGO papers and related composites for flexible energy conversion and storage device applications.

Observation of an Intermediate Band in Sn-doped Chalcopyrites with Wide-spectrum Solar Response

Nanostrcutured particles and polycrystalline thin films of Sn-doped chalcopyrite are synthesized by newly-developed methods. Surprisingly, Sn doping introduces a narrow partially filled intermediate band (IB) located ~1.7 eV (CuGaS2) and ~0.8 eV (CuInS2) above the valance band maximum in the forbidden band gap. Diffuse reflection spectra and photoluminescence spectra reveal extra absorption and emission spectra induced by the IBs, which are further supported by first-principle calculations. Wide spectrum solar response greatly enhances photocatalysis, photovoltaics, and photo-induced hydrogen production due to the intermediate band.

Improved visible-light photocatalysis of nano-Bi2Sn2O7 with dispersed s-bands

Band structure design plays a vital role on the development of highly efficient and visible-light driven photocatalysts. Large band dispersions ensure a fair mobility of the photoinduced charge carriers, leading to excellent photocatalysis. As a case in point, Bi2Sn2O7 has been investigated for the first time as a robust visible-light photocatalyst. The VB and CB are both highly dispersed, and contain s orbitals (Bi 6p + Sn 5s + O 2p for CB, O 2p + Bi 6s for VB). Bi2Sn2O7 was prepared by a direct hydrothermal reaction in the absence of additives and exhibited improved performance. This study not only discloses insights into the design of new photocatalysts in term of band engineering, but also provides flexibility and selectivity for the deliberate synthesis of other functional materials.

Facile and economical exfoliation of graphite for mass production of high-quality graphene sheets

We simulate a micromechanical exfoliation process to design a simple but effective and low-cost strategy for mass production of high-quality graphene sheets by planetary milling with oxalic acid. The selective carboxylation enables oxalic acid molecules to adhere to the edge and defects of graphite like a Scotch tape and plays a crucial role in the non-destructive exfoliation.

(211)-Orientation preference of transparent conducting In2O3:Sn films and its formation mechanism.

Dominantly (211)-oriented In(2)O(3):Sn (ITO) transparent conducting oxide (TCO) films were first fabricated at high sputtering power in the weak reducing ambient with superior electrical and optical properties. The dependence of ITO film orientation on growth condition was systematically investigated, and the formation mechanism was studied by surface energy calculation and band structure simulation. The unique properties of the (211)-oriented films should be ascribed to the richest In-terminated surface of the (211) plane, which is tightly correlated with the comparably highest surface energy and highest conduction band surface comparing with the other two typical planes of (222) and (400). The as-prepared (211)-oriented ITO films with the In-rich ending atoms on the surface are of great significance for the transparent electrode applications.

Oriented single-crystalline nickel sulfide nanorod arrays: "two-in-one" counter electrodes for dye-sensitized solar cells

An oriented millerite nickel sulfide (NiS) nanorod array was successfully grown on bare glass substrate. Metallic conductivity and outstanding electrocatalytic activity make it possible to function as a new type of “two-in-one” counter electrode (CE) in dye-sensitized solar cells (DSCs) to replace both the transparent conductive oxide (TCO) and Pt electrocatalyst. When applied in DSCs, an impressive power conversion efficiency of 7.41% was achieved, comparable to that of TCO supported Pt CE (7.55%). The NiS nanoarray film could be a potential candidate to realize a “two-in-one” CE in DSCs, which is highly desirable to reduce the fabrication cost of DSCs while retaining a comparable conversion efficiency.