Solvent-Free Synthesis of Covalent Organic Framework/Graphene Nanohybrids: High-Performance Faradaic Cathodes for Supercapacitors and Hybrid Capacitive Deionization.

Covalent organic frameworks (COFs) with flexible periodic skeletons and ordered nanoporous structures have attracted much attention as potential candidate electrode materials for green energy storage and efficient seawater desalination. Further improving the intrinsic electronic conductivity and releasing porosity of COF-based materials is a necessary strategy to improve their electrochemical performance. Herein, the employed graphene as the conductive substrate to in situ grow 2D redox-active COF (TFPDQ-COF) with redox activity under solvent-free conditions to prepare TFPDQ-COF/graphene (TFPDQGO) nanohybrids and explores their application in both supercapacitor and hybrid capacitive deionization (HCDI). By optimizing the hybridization ratio, TFPDQGO exhibits a large specific capacitance of 429.0 F g-1 due to the synergistic effect of the charge transport highway provided by the graphene layers and the abundant redox-active centers contained in the COF skeleton, and the assembled TFPDQGO//activated carbon (AC) asymmetric supercapacitor possesses a high energy output of 59.4 Wh kg-1 at a power density of 950 W kg-1 and good cycling life. Furthermore, the maximum salt adsorption capacity (SAC) of 58.4 mg g-1 and stable regeneration performance is attained for TFPDQGO-based HCDI. This study highlights the new opportunities of COF-based hybrid materials acting as high-performance supercapacitor and HCDI electrode materials.

Hydrogen-Bonded Organic Framework Derived 2D N, O Co-Doped Carbon Nanobelt with Tunable Pseudocapacitive Contribution for Efficient Capacitive Deionization.

Defect engineering is recognized as an attractive method for modulating the electronic structure and physicochemical characteristics of carbon materials. Exploiting heteroatom-doped porous carbon with copious active sites has attracted great attention for capacitive deionization (CDI). However, traditional methods often rely on the utilization of additional heteroatom sources and strong corrosive activators, suffering from low doping efficiency, insufficient doping level, and potential biotoxicity. Herein, hydrogen-bonded organic frameworks (HOFs) are employed as precursors to synthesize N, O co-doped porous carbon via a simple and green reverse defect engineering strategy, achieving controllable heavy doping of heteroatoms. The N, O co-doping triggers significant pseudocapacitive contribution and the surface pore structure supports the formation of the electric double layer. Therefore, when HOF-derived N, O co-doped carbon is used as CDI electrodes, a superior salt adsorption capacity of 32.29 ± 1.42 mg g-1 and an outstanding maximum salt adsorption rate of 10.58 ± 0.46 mg g-1 min-1 at 1.6 V in 500 mg L-1 NaCl solution are achieved, which are comparable to those of state-of-the-art carbonaceous electrodes. This work exemplifies the effectiveness of the reverse nitrogen-heavy doping strategy on improving the carbon structure, shedding light on the further development of rational designed electrode materials for CDI.

A Symmetrical Siamese Network Framework With Contrastive Learning for Pose-Robust Face Recognition.

Face recognition has achieved remarkable success owing to the development of deep learning. However, most of existing face recognition models perform poorly against pose variations. We argue that, it is primarily caused by pose-based long-tailed data - imbalanced distribution of training samples between profile faces and near-frontal faces. Additionally, self-occlusion and nonlinear warping of facial textures caused by large pose variations also increase the difficulty in learning discriminative features of profile faces. In this study, we propose a novel framework called Symmetrical Siamese Network (SSN), which can simultaneously overcome the limitation of pose-based long-tailed data and pose-invariant features learning. Specifically, two sub-modules are proposed in the SSN, i.e., Feature-Consistence Learning sub-Net (FCLN) and Identity-Consistence Learning sub-Net (ICLN). For FCLN, the inputs are all face images on training dataset. Inspired by the contrastive learning, we simulate pose variations of faces and constrain the model to focus on the consistent areas between the original face image and its corresponding virtual pose face images. For ICLN, only profile images are used as inputs, and we propose to adopt Identity Consistence Loss to minimize the intra-class feature variation across different poses. The collaborative learning of two sub-modules guarantees that the parameters of network are updated in a relatively equal probability between near-frontal face images and profile images, so that the pose-based long-tailed problem can be effectively addressed. The proposed SSN shows comparable results over the state-of-the-art methods on several public datasets. In this study, LightCNN is selected as the backbone of SSN, and existing popular networks also can be used into our framework for pose-robust face recognition.

Cross-linked amorphous potassium titanate Nanobelts/Titanium carbide MXene nanoarchitectonics for efficient sodium storage at low temperature.

One of the major challenges to improving the performance of sodium-ion batteries at low temperatures is to develop effective anode materials with novel structures and fast reaction kinetics. Currently, converting electrode materials from the crystalline to amorphous state is an effective approach to fabricate the electrode material with high sodium storage performance. Herein, a three-dimensional (3D) cross-linked heterostructure with one-dimensional (1D) amorphous potassium titanate (KTiOx) nanobelts in-situ grown on two-dimensional (2D) titanium carbide (Ti2CTx) nanosheets (a-KTiOx/Ti2CTx) was fabricated through alkalization of the multilayered Ti2CTx MXene, which exhibits remarkable sodium storage performance at both room and low temperatures. The heterostructure prepared by the combination of 1D amorphous nanobelts and 2D conductive nanosheets enables efficient strain alleviation in the electrode, a high capacitive contribution to charge storage, rapid ionic diffusion kinetics, and robust electrode integrity, thus enhancing the sodium storage performance. In particular, reversible capacities of 221.9, 144.2 and 112.6 mAh/g can be achieved at 0.1 A/g after 100 cycles at 25, 0 and -25 °C, respectively. This study provides significant insights into the construction of MXene-based electrode materials for sodium storage at low temperatures.

Ternary-metal Prussian blue analogues as high-quality sodium ion capturing electrodes for rocking-chair capacitive deionization.

Prussian blue analogs (PBAs) have gained much attention in the capacitive deionization (CDI) field because of their rigid open structure and good energy storage capacity. However, their desalination performance is still to be improved for practical application. Herein, we reported the NiCoFe ternary-metal PBAs materials and explored their application as Na+ capturing electrode in rocking-chair capacitive deionization (RCDI) system. On the one hand, the introduction of Ni2+ into CoFe PBA can effectively reduce the lattice changes in the (dis)charging process.On the other hand, the RCDI system with symmetrical structure could avoid the performance deficiency caused by the unbalanced capacity of common HCDI system. Due to the rationalized RCDI cell configuration and ternary-metal PBAs with improved stability, the NiCoFe-PBAs-based RCDI exhibits amazing desalination performance with maximum capacity of 131.4 mg·g-1 and rate of 0.46 mg·g-1·s-1 as well as optimum stability with 90.7 % capacity retention over 300 cycles, surpassing those of PBAs based CDI system reported previously. The special strategy in this work offers inspiration via optimizing the cell structure and electrode materials for the promising development of CDI systems.

Carbon nanotube bridged nickel hexacyanoferrate architecture for high-performance hybrid capacitive deionization.

Although widely used as hybrid capacitive deionization (HCDI) electrode material, the low intrinsic conductivity of metal hexacyanometalate (MHCF) severely hinders the fast insertion/extraction of Na+ in/from its 3D framework structure, damaging its desalination performance. Herein, we design a carbon nanotube (CNT) bridged nickel hexacyanoferrate architecture (NiHCF). The highly conductive CNT not only acts as the skeleton for the uniform growth of NiHCF to provide more ion-accessible surface and active sites but also serves as the conductive bridge to connect the NiHCF particles, which prevents the agglomeration of NiHCF particles and facilitates the charge transfer and ion diffusion during the desalination process. Therefore, the HCDI cell assembled by NiHCF/CNT cathode and AC anode exhibits an excellent desalination performance with a high desalination capacity of 29.1 mg g-1 and a superior desalination rate of 7.2 mg g-1 min-1 in 500 mg L-1 NaCl solution. This work provides a facile method for preparing high-performance MHCF-based electrodes for desalination application.

Prussian blue analogue derived cobalt-nickel phosphide/carbon nanotube composite as electrocatalyst for efficient and stable hydrogen evolution reaction in wide-pH environment.

Transition metal phosphides, especially bimetallic phosphides, are promising noble-metal-free electrocatalysts for hydrogen evolution reaction (HER). However, their inferior charge transfer ability constrains further performance improvement. In this work, a facile strategy is reported to fabricate Co2P/Ni2P/carbon nanotube (CNT) composite from a precursor Co-Ni Prussian blue analogue. The combination of Co2P/Ni2P and CNT endows Co2P/Ni2P/CNT with improved electrical conductivity and a richer electrochemically active surface area. As a result, the Co2P/Ni2P/CNT composite exhibits desirable HER activities across a wide pH range, delivering a benchmark current density of 10 mA cm-2 at overpotentials as low as 151 and 202 mV in 0.5 M H2SO4 and 1 M KOH electrolytes, respectively, as well as remarkable electrocatalytic stabilities over 48 h in both electrolytes. This strategy enables the design of high-performance electrocatalysts for efficient and stable hydrogen generation.

Crosslinking Nanoarchitectonics of Nitrogen-doped Carbon/MoS2 Nanosheets/Ti3 C2 Tx MXene Hybrids for Highly Reversible Sodium Storage.

Although it is a promising sodium storage material due to its excellent electrochemical activity, small bandgap, and large interlayer spacing, layered molybdenum disulfide (MoS2 ) suffers from poor rate capability and degraded cycling life, resulting from its serious aggregation upon preparation, sluggish reaction kinetics, and structure expansion during cycling. To address these issues, a polyethyleneimine (PEI)-assisted fabrication approach was developed for the rational synthesis of an interconnected framework with nitrogen-doped carbon-confined MoS2 nanosheets/Ti3 C2 Tx MXene (MoS2 /Ti3 C2 Tx @NC), where the PEI could guide the uniform growth of MoS2 on Ti3 C2 Tx and the self-generated NC simultaneously enhanced its synergistic coupling with MoS2 /Ti3 C2 Tx , thus contributing to the improvement of charge transfer, diffusion kinetics, and structural integrity of the hybrid electrode. Consequently, the desired MoS2 /Ti3 C2 Tx @NC delivered impressive sodium storage performance, demonstrating high reversible capacities of 397.3 and 206.8 mAh g-1 at 0.1 A g-1 after 100 cycles and 0.5 A g-1 after 500 cycles, respectively. Moreover, electrochemical kinetics analysis and charge storage mechanism manifested that high capacitive contribution, facilitated Na+ transport pathways, and synergistic electronic coupling between MoS2 /Ti3 C2 Tx and NC contributed to the superior sodium storage performance.

Suppressing the oxygen-related parasitic reactions in NaTi2(PO4)3-based hybrid capacitive deionization with cation exchange membrane.

The parasitic reactions leading to capacity fading and charge loss remain a serious issue for capacitive deionization (CDI). NaTi2(PO4)3 (NTP) has recently emerged as a promising faradaic cathode in hybrid CDI (HCDI) with high Na+ uptake capacity and good Na+ selectivity, but it is still challenged by serious parasitic reactions. Although the irreversible faradaic reactions on carbon electrode are raising growing attention in CDI research field, the parasitic reactions on faradaic materials are seldom studied in HCDI by now. In this work, we evaluated the parasitic reactions of NTP-reduced graphene oxide (rGO) electrode in both three-electrode mode and full-cell HCDI mode. By using deaired electrolyte, the coulombic efficiency of NTP-rGO is significantly enhanced from 75.0% to 98.2% in 3rd cycle, and the capacity retention rate is promoted from 37.5% to 80.3% at the low current density of 0.1 mA g-1 in 100 cycles, suggesting that electrochemical reduction of oxygen and its derived reactions are the main parasitic reactions in NTP-based HCDI. In full-cell HCDI desalination tests, by introducing cation exchange membrane to block the penetration of dissolved oxygen, the parasitic reactions and pH fluctuations are successfully suppressed. The study here provides an insight into understanding and suppressing the parasitic reactions in HCDI, and should be of value to the development of efficient and stable HCDI for practical applications.