Jian Pan

Visible Light Responsive Nitrogen Doped Anatase TiO2 Sheets with Dominant {001} Facets Derived from TiN

We demonstrated a facile route for one-pot synthesis of visible light responsive nitrogen doped anatase TiO(2) sheets with dominant {001} facets from TiN. The synthesized anatase TiO(2) sheets show a strong and stable capability of generating photocatalysis active species of *OH radicals and hydrogen evolution from splitting water under visible light irradiation.

Titanium dioxide crystals with tailored facets.

Titanium dioxide (TiO2) has been the most intensively investigated binary transition metal oxide in the past four decades as indicated by Figure S1. Furthermore, the annual number of papers published on TiO2 has seen a continuous increase, particularly since the beginning of this century (Figure S2). This is understandable when one considers the wide range of applications of TiO2 from the conventional areas (i.e., pigment, cosmetic, toothpaste, and paint) to the later developed functional areas such as photoelectrochemical cell,(1-3) dye-sensitized solar cells (DSSCs),(4-11) photocatalysis,(12-24) catalysis,(25-31) photovoltaic cell,(32-34) lithium ion batteries,(35-41) sensors,(42-46) electron field emission,(47-51) microwave absorbing material, biomimetic growth, and biomedical treatments.(52-57) Nearly all these functional applications of TiO2 fall in the scope of energy, environment, and health, which are definitely the three most important and challenging themes facing the Human race that need to be addressed in this century. Besides the apparent merits including nontoxicity, elemental abundance, good chemical stability, and easy synthesis, TiO2 has attracted strong research interest worldwide due to its physicochemical properties for realizing various functions.(15, 58, 59) Especially, very encouraging progresses in photocatalysis and DSSCs with the involvement of TiO2 have greatly stimulated the rapid development of TiO2 crystals with controllable phase, size, shape, defect, and heteroatom.(58, 60-68)

Hydrothermal Synthesis of a Crystalline Rutile TiO2 Nanorod Based Network for Efficient Dye‐Sensitized Solar Cells

One-dimensional (1D) TiO2 nanostructures are desirable as photoanodes in dye-sensitized solar cells (DSSCs) due to their superior electron-transport capability. However, making use of the DSSC performance of 1D rutile TiO2 photoanodes remains challenging, mainly due to the small surface area and consequently low dye loading. Herein, a new type of photoanode with a three-dimensional (3D) rutile-nanorod-based network structure directly grown on fluorine-doped tin oxide (FTO) substrates was developed by using a facile two-step hydrothermal process. The resultant photoanode possesses oriented rutile nanorod arrays for fast electron transport as the bottom layer and radially packed rutile head-caps with an improved large surface area for efficient dye adsorption. The diffuse reflectance spectra showed that with the radially packed top layer, the light-harvesting efficiency was increased due to an enhanced light-scattering effect. A combination of electrochemical impedance spectroscopy (EIS), dark current, and open-circuit voltage decay (OCVD) analyses confirmed that the electron-recombiantion rate was reduced on formation of the nanorod-based 3D network for fast electron transport. As a resut, a light-to-electricity conversion efficiency of 6.31% was achieved with this photoanode in DSSCs, which is comparable to the best DSSC efficiencies that have been reported to date for 1D rutile TiO2 .

A nonstoichiometric SnO2−δ nanocrystal-based counter electrode for remarkably improving the performance of dye-sensitized solar cells

We report the fabrication of a highly active nonstoichiometric SnO2-δ based counter electrode for dye-sensitized solar cells (DSSCs). The introduction of oxygen vacancies into SnO2 results in a much lower charge transfer resistance and a higher polarization current density. The solar energy conversion efficiency of the SnO2-δ based DSSCs is increased by 67%.

A class of transition metal-oxide@MnOx core–shell structured oxygen electrocatalysts for reversible O2 reduction and evolution reactions

It is highly desirable but challenging to develop a highly active as well as durable bifunctional electrocatalyst for the reversible oxygen reduction reaction and evolution reaction (ORR & OER). Here a new class of bifunctional oxygen electrocatalysts has been developed based on ultrafine transition metal-oxide nanoparticles (NPs), such as NiO, FeO or NiFeO, embedded in an amorphous MnOx shell, where the embedded NP core contributes to the high OER activity and the porous amorphous MnOx shell functions as an effective ORR catalyst as well as providing effective structural confinement to the metal-oxide NP core. The best performance was obtained for NiFeO@MnOx, exhibiting a potential gap, ΔE, of 0.798 V to achieve a current of 3 mA cm−2 for the ORR and 5 mA cm−2 for the OER in 0.1 M KOH solution, better than that of Ir/C (0.924 V) and Pt/C (1.031 V). Most importantly, NiFeO@MnOx shows superior stability due to the outstanding structural confinement effect of the amorphous MnOx, achieving a ΔE of 0.881 V after 300 cycles, outperforming 1.093 V obtained for the state-of-the-art Ir–Pt/C oxygen electrocatalysts.

Dye functionalized carbon nanotubes for photoelectrochemical water splitting – role of inner tubes

Dye sensitized water splitting photoelectrochemical (PEC) cells generally require the attachment of photosensitizer to a semiconductor and a water oxidation catalyst (WOC). Here we report for the first time that dye, including zinc phthalocyanine (ZnPc), cobalt phthalocyanine (CoPc) and tris(bipyridine)ruthenium(II) (Rubpy), sensitized or functionalized pristine carbon nanotubes (dye/CNTs) without the presence of semiconducting oxides and conventional WOCs have unusually high activity for PEC water splitting in alkaline solutions under ultraviolet (UV) and visible light. The PEC activities of dye/CNTs show distinctive volcano curves as a function of number of walls with the highest activity observed on double- and triple-walled CNTs (DWNTs and TWNTs). For example, the photocurrent of the ZnPc functionalized TWNTs at 1.2 V vs. RHE is 0.32 mA cm−2, which is ∼4 times of 0.09 mA cm−2 obtained on the ZnPc functionalized single-walled CNTs (SWNTs) and one order of magnitude higher than 0.02 mA cm−2 on ZnPc functionalized multi-walled CNTs (MWNTs). On the other hand, the photocurrents are negligible on pristine CNTs, less than 0.005 mA cm−2 under identical experimental conditions. This remarkable feature is due to the unique charge separation ability of the dye/CNTs, where the photoexcited electrons are transferred to the inner tubes via the electron tunneling under the dc bias voltage, and the significant electrocatalytic activities of DWNTs and TWNTs for the water oxidation reaction. The results provide new opportunities for the development of artificial photosynthetic systems via the manipulation of the quantum properties of CNTs.

Design and synthesis of porous ZnTiO3/TiO2 nanocages with heterojunctions for enhanced photocatalytic H2 production

Despite the tremendous potential applications of hollow micro/nanostructures, their composition has been limited to mainly single chemical compounds. Inspired by recent innovations in the areas of metal organic frameworks (MOFs) and nanocoating, here, we report the rational synthesis of mesoporous ZnTiO3/TiO2 hollow polyhedra (MZTHP) obtained by hydrothermal treatment of zeolitic imidazolate framework-8 (ZIF-8)@TiO2 core–shell polyhedral particles. The subsequent calcination of these particles caused phase transformation from TiO2 to ZnTiO3 and eventually induced the formation of Zn2TiO4. In addition, the fabrication of these hollow structures revealed a way for the preparation of hollow polyhedral photocatalysts with Pt nanoparticles deposited onto their external surface (PHS-1) or encapsulated inside their hollow structures (PHS-2). Importantly, these two types of Pt-decorated nanoparticles are shown to exhibit an improved yet distinctly different performance for photocatalytic hydrogen production, highlighting that the photocatalytic activity correlates with the Pt location and dispersion.

Structurally confined ultrafine NiO nanoparticles on graphene as a highly efficient and durable electrode material for supercapacitors

The most significant challenge in the development of ultrafine oxide based supercapacitors is the poor microstructure stability due to the rapid agglomeration of the fine nanoparticles (NPs). Here, we developed novel amorphous MnOx structurally confined ultrafine NiO NPs (∼2.3 nm) supported on graphene, NiO@MnOx via a simple and facile self-assembly process with the assistance of microwave sintering. NiO@MnOx with a NiO : MnOx weight ratio of 1 : 0.2 achieves a high capacitance of 966 F g−1 based on total electrode materials and 3222 F g−1 based on active materials at a discharge current density of 2 A g−1. Remarkably, the materials retain 100% capacitance after 2000 cycles at a charge and discharge current of 10 A g−1. In contrast, the durability of ultrafine NiO NPs without MnOx confinement is very poor, with 94% of the capacitance lost under identical cyclic conditions despite the initial high capacitance of 3696 F g−1. The substantially enhanced capacitance, durability and high rate capacity contribute to the formation of a nanoporous and amorphous MnOx layer on ultrafine NiO NPs, which provides the extraordinary structural confinement and enhances the mass transfer process. The results provide a new strategy to develop highly efficient and durable ultrafine nanosized electrode materials for supercapacitors.

Synthesis of nitrogen doped faceted titanium dioxide in pure brookite phase with enhanced visible light photoactivity

Brookite titanium dioxide (TiO2) is rarely studied, as compared with anatase and rutile phases TiO2, due to its comparatively lower photoactivity. It has been recently reported that brookite TiO2 with active facets exhibits excellent performance, however, synthesis of such faceted brookite TiO2 is difficult because of its low thermodynamic phase stability and low structural symmetric. Furthermore, like faceted anatase and rutile TiO2, faceted brookite TiO2 is not responsive to visible light due to its wide bandgap. In this study, a novel dopant, hydrazine, was introduced in the development of nitrogen doping. By applying this dopant, nitrogen doped brookite nanorods with active {120}, {111} and {011¯} facets were successfully synthesized. The resultant materials exhibited remarkably enhanced visible-light photoactivity in photodegradation.

Advanced yolk-shell nanoparticles as nanoreactors for energy conversion

Abstract Yolk-shell structured nanoparticles are of immense scientific and technological interests because of their unique architecture and myriad of applications. This review summarizes recent progresses in the use of yolk-shell structured nanoparticles as nanoreactors for various chemical reactions. A very brief overview of synthetic strategies is provided with emphasis on recent research progress in the last five years. Catalytic applications of these yolk-shell structured nanoreactors are then discussed by covering photocatalysis, methane reforming and electrochemical conversion. The state of the art research and perspective in future development are also highlighted.