Space charge transfer is crucial for an efficient electrocatalytic
process, especially for narrow-band-gap metal sulfides/selenides.
Herein, we designed and synthesized a core–shell structure
which is an ultrathin MoSe2 nanosheet coated CuS hollow
nanoboxes (CuS@MoSe2) to form an open p–n junction
structure. The space charge effect in the p–n junction region
will greatly improve electron mass transfer and conduction, and also
have abundant active interfaces. It was used as a bifunctional electrocatalyst
for water oxidation at a wide pH range. It exhibits a low overpotential
of 49 mV for the HER and 236 mV for the OER at a current density of
10 mA·cm
–2 in acidic pH, 72 mV
for the HER and 219 mV at 10 mA·cm
–2 for the OER in alkaline pH, and 62 mV for the HER and 230 mV at
10 mA·cm
–2 for the OER under neutral
conditions. The experimental results and density functional theory
calculations testify that the p–n junction in CuS@MoSe2 designed and synthesized has a strong space charge region
with a synergistic effect. The built-in field can boost the electron
transport during the electrocatalytic process and can stabilize the
charged active center of the p–n junction. This will be beneficial
to improve the electrocatalytic performance. This work provides the
understanding of semiconductor heterojunction applications and regulating
the electronic structure of active sites.
Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. The regulation of the local electronic structure of the active metal sites in polymetallic composites provides a basic idea. Herein, the ultrathin bimetallic molybdate nanosheets are evenly deposited on the CuOx hollow nanotubes on the copper foam substrate to form a hierarchical heterostructure, which can be used as an efficient bifunctional electrocatalyst for overall water splitting. Experimental results prove that the introduction of Ni to form a double metal salt molybdate and CuOx heterostructure design can be optimized by Co cation as best electronic structure of electric catalytic activity center, and can effectively promote the generation of CoOOH active phase at the same time, so that can skillfully optimize the binding strength between the Co site and the oxygen‐containing intermediate, and enhancing catalytic activity. When it is used in the overall water splitting of a double‐electrode alkaline electrolytic cell, the cell voltage of CoNiMoO4‐21/CuOx/CF is 1.532 V at 50 mA cm−2, far exceeding most of the reported conventional bifunctional electrocatalyst. This work has contributed to understanding the central active sites of polymetallic composites and has provided a useful value for the design of efficient electrocatalysts.
In this paper, we introduce a fully automatic framework for 3D face recognition under expression variation. For 3D data preprocessing, an improved nose detection method is presented. The small pose is corrected at the same time. A new facial expression processing method which is based on sparse representation is proposed subsequently. As a result, this framework enhances the recognition rate because facial expression is the biggest obstacle for 3D face recognition. Then, the facial representation, which is based on the dual-tree complex wavelet transform (DT-CWT), is extracted from depth images. It contains the facial information and six subregions' information. Recognition is achieved by linear discriminant analysis (LDA) and nearest neighbor classifier. We have performed different experiments on the Face Recognition Grand Challenge database and Bosphorus database. It achieves the verification rate of 98.86% on the all vs. all experiment at 0.1% false acceptance rate (FAR) in the Face Recognition Grand Challenge (FRGC) and 95.03% verification rate on nearly frontal faces with expression changes and occlusions in the Bosphorus database.
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