Guodong Wei

Interface engineering of 3D BiVO4/Fe-based layered double hydroxide core/shell nanostructures for boosting photoelectrochemical water oxidation

Photoelectrochemical water oxidation driven by photocatalysts is one of the most effective ways for converting solar energy into fuels and chemicals. However, to date, the solar conversion efficiency using the established photocatalysts is still low. Herein, we report a new strategy for making a class of three-dimensional (3D) BiVO4/Fe-based (Ni1−xFex and Co1−xFex) layered double hydroxide (LDH) interface heterostructures for boosting the photoelectrocatalytic water oxidation performance. Compared with the BiVO4, the BiVO4/Ni0.5Fe0.5–LDH interface photoanode exhibits about 4-fold photocurrent enhancement at 1.23 V vs. the reversible hydrogen electrode and remarkable negative shift (320 mV) of the onset potential for the oxygen evolution reaction (OER). Theoretical calculations reveal that the enhanced photocatalysis for the OER is mainly attributed to the optimal light absorption and the acceleration of electron–hole separation enabled by the strong electronic coupling at the BiVO4/NiFe–LDH interface. The present work first highlights the importance of tuning the light absorption and the separation of carriers using interface engineering in enhancing the solar photocatalytic performance.

Hierarchical NiCoP nanocone arrays supported on Ni foam as an efficient and stable bifunctional electrocatalyst for overall water splitting

Design of cost-effective, highly efficient and stable bifunctional electrocatalysts for overall water splitting is necessary for renewable energy systems. In this study, NiCoP nanowire arrays grown on 3D Ni foam (NiCoP NWAs/NF) were successfully synthesized by a two-step method, which were developed as novel bifunctional electrocatalysts for evaluating in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Their special cone nanostructure and bifunctional crystal structure enable the electrocatalysts to display remarkable electrocatalytic performance and stability for OER and HER (maintained for 28 h in the long-term HER and OER stability test with slight attenuation). The electrodes have very low overpotentials of 197 mV and 370 mV for HER and OER in 1.0 M KOH at a high current density of 100 mA cm−2, respectively. All the merits can be attributed to several parameters: the inherent nature of transition metal phosphides, the presence of a bimetal synergetic effect, special morphology design, and the formation of “secondary” electrocatalysts on the surface of NiCoP. Meanwhile, the excellent bifunctional electrocatalysts can be developed as both anode and cathode of an alkaline electrolyzer (1.0 M KOH) which needs a cell voltage of 1.64 V to achieve 20 mA cm−2 current density.

Flexible MXene–graphene electrodes with high volumetric capacitance for integrated co-cathode energy conversion/storage devices

Developing self-powered integrated energy conversion and storage devices (ECSDs) is regarded as a promising approach to meet the quickly increasing demand for portable and wearable electronics. In this work, we describe a concept of using reduced graphene oxide (rGO) as a binder bridging electrochemically active conducting particles and enabling the manufacturing of flexible all-solid-state rGO/Ti3C2Tx (MXene) film-based supercapacitors. These supercapacitors were integrated with flexible thin-film solar cells by the co-cathode method to fabricate ECSDs. The porous rGO/Ti3C2Tx films were produced by vacuum-assisted filtration of the GO/Ti3C2Tx dispersion, followed by reduction at 300 °C under vacuum. This approach eliminated the need for the delamination of MXenes and allowed for the manufacturing of thick electrodes with good electrolyte accessibility. The volumetric and gravimetric capacitance of the rGO/Ti3C2Tx film in 6 M KOH reached 370 F cm−3 and 405 F g−1, respectively, which can be related to the synergistic effect of rGO and Ti3C2Tx. The assembled all-solid-state supercapacitors (SCs) using the polyvinyl alcohol (PVA)/KOH gel electrolyte exhibited a high energy density of 63 mW h cm−3 at a power density of 0.06 W cm−3. Their capacitance did not change after 10u2006000 charge/discharge cycles at the current density of 5 A g−1, ensuring stable performance of the ECSDs.

Mesoporous NiCo2O4 nanospheres with a high specific surface area as electrode materials for high-performance supercapacitors

Ternary nickel cobaltite (NiCo2O4) has attracted more and more attention as a promising electrode material for high performance supercapacitors (SCs) due to its high theoretical capacity, unique crystal structure and excellent electronic conductivity. In this study, a template-free chemical co-precipitation method as a general strategy has been easily developed to fabricate mesoporous NiCo2O4 nanospheres with a high specific surface area of 216 m2 g−1, which can be further self-assembled into 3D frameworks. The key to the formation of mesoporous NiCo2O4 nanospheres with a desired pore-size distribution centered at ∼2.4 nm is a unique preparation method assisted with sodium bicarbonate as a complex agent. When tested as electrode materials for SCs, the NiCo2O4 electrodes delivered excellent electrochemical performances with high specific capacitance (842 F g−1 at a current density of 2 A g−1), superior cycling stability with no capacity decrease after 5000 cycles (103% initial capacity retention), and great rate performance at a 10-time current density increase (79.9% specific capacitance retention). Furthermore, as expected in a NiCo2O4-based asymmetric supercapacitor device, a superior energy density as high as 29.8 W h kg−1 at a power density of 159.4 W kg−1 could be achieved. These results highlight a general, eco-friendly, template-free strategy for the scale-up fabrication of a promising mesoporous NiCo2O4 electrode material for high-performance SC applications.

Flexible Supercapacitors Based on Polyaniline Arrays Coated Graphene Aerogel Electrodes

Flexible supercapacitors(SCs) made by reduced graphene oxide (rGO)-based aerogel usually suffer from the low energy density, short cycle life and bad flexibility. In this study, a new, synthetic strategy was developed for enhancing the electrochemical performances of rGO aerogel-based supercapacitor via electrodeposition polyaniline arrays on the prepared ultralight rGO aerogel. The novel hybrid composites with coated polyaniline (PANI) arrays growing on the rGO surface can take full advantage of the rich open-pore and excellent conductivity of the crosslinking framework structure of 3D rGO aerogel and high capacitance contribution from the PANI. The obtained hybrid composites exhibit excellent electrochemical performance with a specific capacitance of 432xa0Fxa0g-1 at the current density of 1 A g-1, robust cycling stability to maintain 85% after 10,000 charge/discharge cycles and high energy density of 25xa0Wxa0hxa0kg-1. Furthermore, the flexible all-solid-state supercapacitor have superior flexibility and outstanding stability under different bending states from the straight state to the 90° status. The high-performance flexible all-solid-state SCs together with the lighting tests demonstrate it possible for applications in portable electronics.

Experimental and theoretical studies of nonlinear dependence of the internal resistance and electrode thickness for high performance supercapacitor

In this study, the internal resistance with the increasing of electrode thickness in a typical nanoporous carbon-based supercapacitor and their corresponding electrochemical performances were designed and investigated in detail. As for the carbon-based double electrode layer electrochemical system, electrochemical experiments greatly support the fact of nonlinear dependence and indicate that the curve of internal resistance vs. electrode thickness can have a minimum value when the thickness increasing from 10 to 140u2009μm. To explain the underlying mechanisms responsible for the nonlinear dependence, a theoretical model based on a porous electrode/electrolyte electrochemical system was proposed. As expected, the results of calculations carried out in the framework of the proposed model can be very good agreement with the experimental data. According to the calculation, the optimized electrode thickness is 53.1u2009μm corresponding to the minimum value of SC internal resistance. Obviously, the current research results might greatly support the nonlinear conclusion instead of linear relationship between the internal resistance and the electrode thickness and may shed some light on the fabrication and exploration of supercapacitors with high power density.

Single-crystalline integrated 4H-SiC nanochannel array electrode: toward high-performance capacitive energy storage for robust wide-temperature operation

The exploration of energy conversion and storage devices for wide-temperature operation is presently a grand challenge. Herein, the single-crystalline integrated energy-storage units based on highly-oriented 4H-SiC nanochannel arrays (NCAs) were fabricated via an improved electrochemical anodic oxidation technique from 4H-SiC wafers. The as-prepared SiC NCAs electrode exhibits an areal capacitance of 14.8 mF cm−2 at 10 mV s−1, which is the highest for SiC electrodes ever reported and also 6-fold higher in comparison to that of SiC nanowire array electrode (NWAs, 2.32 mF cm−2). Moreover, the resultant 4H-SiC NCAs exhibit an extremely stable cycling performance in aqueous electrolytes, with higher than 95% retention of initial capacitance regardless of being serviced under low, high or cross-fade temperatures for 11u2006000 charge–discharge cycles, demonstrating that they are nearly full-featured for robust wide-temperature operation.