Guoge Zhang

A facile route to fabricate an anodic TiO2 nanotube-nanoparticle hybrid structure for high efficiency dye-sensitized solar cells.

The relatively low internal surface area of anodized TiO(2) nanotube arrays (TNAs) limits dye adsorption and light capturing in TNA-based dye-sensitized solar cells (DSSCs). Here, water treatment of as-anodized TNAs at room temperature was used to tailor the geometry of TNA walls in a controllable way, leading to a hybrid tube wall structure with the outer shell in a tubular morphology and the inner surface consisting of small particles. To enable front-side illumination in DSSCs, the TNAs with porous inner walls were transferred to transparent conductive oxide substrates by a self-detaching and transfer technique. The roughened water-treated TNAs show significantly enhanced internal surface area, leading to improved dye-loading and light-harvesting capabilities. Optimized performance was achieved after water treatment for 2 days, with a power conversion efficiency of 6.06%, increased by ∼33% compared to conventional TNAs. Furthermore, the hybrid TNA nanostructure provides excellent electron transfer and recombination characteristics, thus promising for high efficiency DSSCs.

Sponge-like Ni(OH)2–NiF2 composite film with excellent electrochemical performance

Sponge-like porous Ni(OH)(2)-NiF(2) composite (PNC) film was successfully synthesized by the anodization of nickel in a NH(4)F and H(3)PO(4) containing electrolyte. Thanks to the good conductivity and the highly porous architecture, PNC exhibited not only a high specific capacitance, but also a superior rate capability and a good cyclability (2090 F g(-1) at 10 mV s(-1), capacitance >1200 F g(-1) at 100 A g(-1) after 2000 cycles). Anodization of nickel is proven to be fast and facile and can be easily scaled up. The method described here is promising for the fabrication of supercapacitor electrodes with excellent performance.

Enhanced charge storage by the electrocatalytic effect of anodic TiO2 nanotubes

Ordered titania nanotube (TNT) arrays were fabricated by anodization of titanium with a very fast voltage ramp speed. Co(OH)(2)/TNT nanocomposite was synthesized by cathodic deposition using the as-anodized TNT as the substrate. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, crystalline structure and chemical state. The capacitive characteristics were investigated by cyclic voltammetry (CV), charge-discharge tests, and electrochemical impedance spectroscopy (EIS). Thanks to the electrocatalytic effect of the as-anodized TNTs on the reduction of Co(OH)(2), the Co(OH)(2)/TNT composite electrode exhibits a significantly enhanced charge storage capacity (an increase of 73%) when compared with Co(OH)(2)/Ti (titanium as the deposition substrate). The occurrence of such an electrocatalytic effect is suggested to be related to the nano-sized TiO(2) crystals (rutile) embedded in organized amorphous TNTs. Co(OH)(2)/TNT demonstrates enhanced specific energy, high rate capability and good cyclability, and can be a potential electrode of choice for supercapacitors.

Ni@NiO core/shell dendrites for ultra-long cycle life electrochemical energy storage

A dendritic Ni@NiO core/shell electrode (DNE) is successfully fabricated by electrodeposition in a Ni-free electrolyte, with a Ni anode providing Ni ions through dissolution and diffusion. The unique structure is ideal for electrochemical energy storage since the dendrites provide a large surface area for easy electrolyte infiltration; the metal core improves the electrode conductivity with a shortened ion diffusion path, and the metal oxide shell is active for faradaic charge storage. As a result, the synthesized DNE demonstrates a high specific capacitance of 1930 F g−1 and a high areal capacitance of 1.35 F cm−2, with super-long cycle stability. The gravimetric capacitance of the DNE hardly shows any decay after 70 000 cycles at a scan rate of 100 mV s−1. It was also demonstrated that our electrodeposition method in a source-free electrolyte is universal to deposit dendritic Ni-compounds on many other types of substrates, versatile for different applications.

Boosting the oxygen evolution reaction in non-precious catalysts by structural and electronic engineering

The oxygen evolution reaction (OER) plays a key role in many energy storage applications. It remains a big challenge to fabricate non-precious OER electrocatalysts with both excellent activity and high stability. Herein, we demonstrate that excellent OER performance can be achieved by applying structural and electronic engineering simultaneously. As a proof of concept, 1D vertically aligned Ni3S2 nanorods (without any entangled or inter-crossed nanostructure on the top) are firstly synthesized to provide both conducting highways and rich active sites with significantly facilitated gas release during the OER. A highly active Ni–Fe layered double hydroxide (LDH) nanofilm is then prepared on the Ni3S2 nanorod to form a core@shell structure. The strong interfacial coupling between the in situ grown Ni–Fe LDH and Ni3S2 creates abundant oxygen vacancies to effectively lower the adsorption energy of OH−. Consequently, Ni3S2@Ni–Fe LDH exhibits superior OER activity and outstanding stability. The overpotential of Ni3S2@Ni–Fe LDH prepared on nickel foam is only 190 mV at 10 mA cm−2 and the Tafel slope is as low as 38 mV dec−1. The OER performance remains constant after 40 hours of water electrolysis. Our material is among the best non-precious OER catalysts reported so far. The methodology of enhancing the catalytic performance reported here can be extended to other materials for the design and fabrication of low cost OER catalysts with excellent activity.

Black phosphorus quantum dots as dual-functional electron-selective materials for efficient plastic perovskite solar cells

Organic–inorganic hybrid metal halide perovskite solar cells (PSCs) have attracted tremendous research interest due to their high power conversion efficiency and simple fabrication. However, the exploitation of new electron-selective materials which can simultaneously tailor the quality of metal halide perovskite film for low-temperature-produced plastic organic–inorganic halide perovskite solar cells (PSCs) is of key importance but remains a great challenge. Herein, facile solution-processed black phosphorus quantum dots (BPQDs) with ambipolar conductivity are developed as dual-functional electron-selective layer (ESL) in plastic PSCs. The BPQD ESL plays crucial roles in both forming a cascade energy level for fast electron extraction and guiding the crystallization behavior of the perovskite to yield compact perovskite films with less traps, good crystallization and ordered orientation. The perovskite films deposited on the BPQD ESL exhibit excellent optoelectronic properties, and the resulting plastic planar perovskite solar cells possess a reasonably high efficiency of 11.26%. The 3.15-fold enhancement in efficiency arises from both the efficient electron extraction and suppressed radiative and trap-assisted non-radiative recombination compared with the devices built on the bare ITO surface without an ESL. This work paves a promising way for developing novel electron-selective non-oxide materials for highly efficient solar cells.

Facile synthesis of Mn-doped TiO 2 nanotubes with enhanced visible light photocatalytic activity

AbstractTitanium dioxide is a promising photocatalyst and has been widely used in many applications. However, it remains challenging to improve the photocatalytic performance of TiO2 under visible light illumination. Herein, a facile one step method was put forward to produce Mn-doped TiO2 nanotube arrays (TNTs) without the formation of manganese oxides. Intermediate band states were generated in Mn-doped TNTs, leading to enhanced visible light absorption and more efficient separation of photo-generated electron–hole pairs. The visible light photocatalysis of Mn-doped TNTs was significantly improved. The method reported here might be extended to the doping of other elements in TNTs and provides opportunities for the design of advanced photocatalysts.Graphical AbstractMn-doped TiO2 nanotubes were developed by a facile method without the formation of separate manganese oxides, which demonstrated significantly improved photocatalytic performance under visible light illumination.