Dekang Huang

Electrochemically Reduced Graphene Oxide Multilayer Films as Efficient Counter Electrode for Dye-Sensitized Solar Cells

We report on a new counter electrode for dye-sensitized solar cells (DSCs), which is prepared using layer-by-layer assembly of negatively charged graphene oxide and positively charged poly (diallyldimethylammonium chloride) followed by an electrochemical reduction procedure. The DSC devises using the heteroleptic Ru complex C106TBA as sensitizer and this new counter electrode reach power conversion efficiencies of 9.5% and 7.6% in conjunction with low volatility and solvent free ionic liquid electrolytes, respectively. The new counter electrode exhibits good durability (60°C for 1000 h in a solar simulator, 100 mW cm−2) during the accelerated tests when used in combination with an ionic liquid electrolyte. This work identifies a new class of electro-catalysts with potential for low cost photovoltaic devices.

Porous Li4Ti5O12–TiO2 nanosheet arrays for high-performance lithium-ion batteries

This work reports on porous Li4Ti5O12 (LTO)–TiO2 nanosheet arrays prepared via a versatile hydrothermal method for lithium ion batteries, exhibiting a high initial discharge capacity of 184.6 mA h g−1 at 200 mA g−1 and possessing excellent electrochemical stability with only 8.3% loss of specific capacity at 1 A g−1 in a prolonged charge–discharge process (1000 cycles). The excellent electrochemical performance can be attributed to the interconnected mesoporous/macroporous structures and the abundant grain boundaries generated by the existing multiphase materials, as well as the direct connection between the nanoarrays and conductive Ti substrates which facilitates the lithium ion and electron transportation. A flexible lithium ion battery has been further designed by using the nanosheet LTO–TiO2 arrays as the anode and LiCoO2 as the cathode, enabling it to reliably power an LED light under severe mechanical bending. This is very promising for future potential application in high performance flexible energy storage devices.

Active catalysts based on cobalt oxide@cobalt/N-C nanocomposites for oxygen reduction reaction in alkaline solutions

Over the past few years, electrocatalysis for the oxygen reduction reaction in alkaline solutions has undergone tremendous advances, and non-precious metal catalysts are of prime interest. In this study, we present a highly promising CoO@Co/N-C (where N-C represents a N-doped carbon material) catalyst, achieving an onset potential of 0.99 V (versus the reversible hydrogen electrode (RHE)) and a limiting current density of 7.07 mA·cm−2 (at 0.3 V versus RHE) at a rotation rate of 2,500 rpm in an O2-saturated 0.1 M KOH solution, comparable to a commercial Pt/C catalyst. The H2-O2 alkaline fuel cell test of CoO@Co/N-C as the cathode reveals a maximum power density of 237 mW·cm−2. Detailed investigation clarifies that a synergistic effect, induced by C-N, Co-N-C, and CoO/Co moieties, is responsible for the bulk of the gain in catalytic activity.

Electrochemically reduced graphene oxide multilayer films as metal-free electrocatalysts for oxygen reduction

In this work we report on functional multilayer films containing electrochemically reduced graphene oxide (ERGO) by the alternating layer-by-layer (LBL) assembly of negatively charged graphene oxide (GO) and positively charged poly (diallyldimethylammonium chloride) (PDDA) in combination with an electrochemical reduction procedure. As a metal-free catalyst, the resulting [PDDA@ERGO] multilayer film possesses a remarkable electro-catalytic activity toward the oxygen reduction reaction (ORR) with superior methanol tolerance in alkaline media. Further research indicates that the unusual catalytic activity of the prepared hybrid films arises from synergetic chemical coupling effects between PDDA and ERGO. Importantly, the [PDDA@ERGO] multilayer film as a metal free oxygen reduction catalyst reported here is easy to build up with the advantages of fine control of the film thickness, being energy effective, fast and green without using dangerous and corrosive substances.

Rutile-TiO2 decorated Li4Ti5O12 nanosheet arrays with 3D interconnected architecture as anodes for high performance hybrid supercapacitors

Herein, we report on rutile TiO2 decorated hierarchical Li4Ti5O12 nanosheet arrays for lithium ion hybrid supercapacitor application for the first time. It is noted that the self-supported arrays manifest impressive rate capability and cycling stability, showing a reversible specific capacity of 142.9 mA h g−1, and retaining 92.3% of their initial capacity over 3000 cycles at a rate of 30C. The lithium ion hybrid supercapacitor, constructed with Li4Ti5O12 nanosheet arrays and nitrogen doped carbon nanotubes (N-CNTs), exhibits an ultrahigh energy density of 74.85 W h kg−1 at a power density of 300 W kg−1. The hierarchical 3D interconnected nanostructure of the self-supported Li4Ti5O12–rutile TiO2 nanosheet arrays, as well as the efficient lithium diffusion along the [011] direction for Li4Ti5O12 and [001] for rutile TiO2, play an important role in the outstanding energy storage performance.

Potassium-Doped Zinc Oxide as Photocathode Material in Dye-Sensitized Solar Cells

ZnO nanoparticles are doped with K and applied in p-type dye-sensitized solar cells (DSCs). The microstructure and dynamics of hole transportation and recombination are investigated. The morphology of the K-doped ZnO nanoparticles shows a homogeneous distribution with sizes in the range 30-40 nm. When applied in p-type DSCs in combination with C343 as sensitizer, the K-doped ZnO nanoparticles achieve a photovoltaic power conversion efficiency of 0.012 % at full-intensity sunlight. A further study on the device by transient photovoltage/photocurrent decay measurements shows that the K-doped ZnO nanoparticles have an appreciable hole diffusion coefficient (ca. 10(-6) cm(2) s(-1) ). Compared to the widely used p-type NiO nanoparticles, this advantage is crucial for further improving the efficiency of p-type DSCs.

Hydrogen peroxide biosensor based on microperoxidase-11 immobilized on flexible MWCNTs-BC nanocomposite film.

In the present work, we report on an experimental study of flexible nanocomposite film for electrochemical detection of hydrogen peroxide (H2O2) based on bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs) in combination with microperoxidase-11 (MP-11). MWCNTs are used to functionalize BC and provide a flexible conductive film. On the other hand, BC can improve MWCNTs׳ biocompatibility. The investigation shows that MP-11 immobilized on the flexible film of MWCNTs-BC can easily present a pair of well-defined and quasi-reversible redox peaks, revealing a direct electrochemistry of MP-11 on the nanocomposite film. The apparent heterogeneous electron-transfer rate constant ks is estimated to be 11.5s(-1). The resulting flexible electrode presents appreciated catalytic properties for electrochemical detection of H2O2, comparing to traditional electrodes (such as gold, glassy carbon electrode) modified with MP-11. The proposed biosensor exhibits a low detection limit of 0.1 µM (at a signal-to-noise ratio of 3) with a linear range of 0.1-257.6 µM, and acquires a satisfactory stability.

Co9S8 hollow spheres for enhanced electrochemical detection of hydrogen peroxide

This work reports on an experimental investigation of Co9S8 hollow spheres with excellent interfacial charge transfer ability for the electrochemical detection of hydrogen peroxide and glucose in alkaline environment. The result reveals that the Co9S8 hollow spheres exhibit excellent electrocatalytic activity for the reduction of hydrogen peroxide. An electrochemical sensor based on Co9S8 can be further realized, exhibiting a linear response range from 0.0001 to 11.11mM for hydrogen peroxide with a low detection limit of 0.02μM, and a high sensitivity of 267.2mA mol(-1)cm(-2), which is one of the highest values among the non-enzymatic sensors based on inorganic oxides. The Co9S8 sensor also exhibits good response toward glucose at different concentrations. These results demonstrate that the as-prepared Co9S8 hollow spheres have a potential application in the development of sensors for enzyme-free detection of H2O2 and glucose.

Engineering NiS/Ni2P Heterostructures for Efficient Electrocatalytic Water Splitting

Developing high-active and low-cost bifunctional materials for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) holds a pivotal role in water splitting. Therefore, we present a new strategy to form NiS/Ni2P heterostructures. The as-obtained NiS/Ni2P/carbon cloth (CC) requires overpotentials of 111 mV for the HER and 265 mV for the OER to reach a current density of 20 mA cm-2, outperforming their counterparts such as NiS and Ni2P under the same conditions. Additionally, the NiS/Ni2P/CC electrode requires a 1.67 V cell voltage to deliver 10 mA cm-2 in a two-electrode electrolysis system, which is comparable to the cell using the benchmark Pt/C||RuO2 electrode. Detailed characterizations reveal that strong electronic interactions between NiS and Ni2P, abundant active sites, and smaller charge-transfer resistance contribute to the improved HER and OER activity.

Support-dependent active species formation for CuO catalysts: Leading to efficient pollutant degradation in alkaline conditions

Redox metal ions play the crucial role in versatile advanced oxidation technologies, in which controlling the active species formation through catalyst design is one of the key challenges in oxidant utilization. This work describes an example of different active species formations in CuO-mediated degradation just because of supporting material differences. Although three CuO catalysts were prepared by similar procedures, it was found that CuO-MgO catalyst demonstrated high efficiency in phenol degradation with bicarbonate activated H2O2, in which the superoxide radical is crucial, while hydroxyl radical and singlet oxygen are ignorable. For the CuO-MgO-Al2O3 and CuO-Al2O3 catalysts, the degradation proceeds by popular hydroxyl radical based process, however, the efficiency was poor. The EPR experiments also confirmed the absence of hydroxyl radical in CuO-MgO system but its presence in CuO-MgO-Al2O3 and CuO-Al2O3 system. The high catalytic efficiency with ignorable hydroxyl radical in the CuO-MgO system leads us to propose that an alternative Cu(III) species dominates the degradation. The basic MgO support may facilitate the formation of the Cu(III) species, whereas the neutral MgO-Al2O3 and acidic Al2O3 supports are unable to stabilize the high valent Cu(III) species, leading to the common hydroxyl radical mechanism with low efficiency of H2O2 in alkaline conditions.