Electrochemically Dealloying Engineering toward Integrated Monolithic Electrodes with Superior Electrochemical Li-Storage Properties.

Integrated monolithic electrodes (IMEs) free of inactive components demonstrate great potential in boosting energy-power densities and cycling life of lithium-ion batteries. However, their practical applications are significantly limited by low active substance loading (< 4.0 mg cm-2 and 1.0 g cm-3), complicated manufacturing process, and high fabrication cost. Herein, employing industrial Cu-Mn alloy foil as a precursor, a simple neutral salt solution-mediated electrochemical dealloying strategy is proposed to address such problems. The resultant Cu-Mn IMEs achieve not only a significantly larger active material loading due to the in situ generated Cu2O and MnOx (ca. 16.0 mg cm-2 and 1.78 g cm-3), simultaneously fast transport of ions and electrons due to the well-formed nanoporous structure and built-in Cu current collector, but also high structural stability due to the interconnected ligaments and suitable free space to relieve the volume expansion upon lithiation. As a result, they demonstrate remarkable performances including large specific capacities (> 5.7 mAh cm-2), remarkable pseudocapacitive effect despite the battery-type constitutes, long cycling life, and good working condition in a lithium-ion full cell. This study sheds new light on the further development of IMEs, enriches the existing dealloying techniques, and builds a bridge between the two.

High-Pressure-Field Induced Synthesis of Ultrafine-Sized High-Entropy Compounds with Excellent Sodium-Ion Storage.

Emerging high entropy compounds (HECs) have attracted huge attention in electrochemical energy-related applications. The features of ultrafine size and carbon incorporation show great potential to boost the ion-storage kinetics of HECs. However, they are rarely reported because high-temperature calcination tends to result in larger crystallites, phase separation, and carbon reduction. Herein, using the NaCl self-assembly template method, by introducing a high-pressure field in the calcination process, the atom diffusion and phase separation are inhibited for the general formation of HECs, and the HEC aggregation is inhibited for obtaining ultrafine size. The general preparation of ultrafine-sized (<10 nm) HECs (nitrides, oxides, sulfides, and phosphates) anchored on porous carbon composites is realized. They are demonstrated by combining advanced characterization technologies with theoretical computations. Ultrafine-sized high entropy sulfides-MnFeCoCuSnMo/porous carbon (HES-MnFeCoCuSnMo/PC) as representative anodes exhibit excellent sodium-ion storage kinetics and capacities (a high rating capacity of 278 mAh g-1 at 10 A g-1 for full cell and a high cycling capacity of 281 mAh g-1 at 20 A g-1 after 6000 cycles for half cell) due to the combining advantages of high entropy effect, ultrafine size, and PC incorporation. Our work provides a new opportunity for designing and fabricating ultrafine-sized HECs.

Architecting Braided Porous Carbon Fibers Based on High-Density Catalytic Crystal Planes to Achieve Highly Reversible Sodium-Ion Storage.

Carbonaceous materials are considered strong candidates as anode materials for sodium-ion batteries (SIBs), which are expected to play an indispensable role in the carbon-neutral era. Herein, novel braided porous carbon fibres (BPCFs) are prepared using the chemical vapour deposition (CVD) method. The BPCFs possess interwoven porous structures and abundant vacancies. The growth mechanism of the BPCFs can be attributed to the polycrystalline transformation of the nanoporous copper catalyst in the early stage of CVD process. Density functional theory calculations suggest that the Na+ adsorption energies of the mono-vacancy edges of the BPCFs (-1.22 and -1.09 eV) are lower than that of an ideal graphene layer (-0.68 eV), clarifying in detail the adsorption-dominated sodium storage mechanism. Hence, the BPCFs as an anode material present an outstanding discharge capacity of 401 mAh g-1 at 0.1 A g-1 after 500 cycles. Remarkably, this BPCFs anode, under high-mass-loading of 5 mg cm-2, shows excellent long-term cycling ability with a reversible capacity of 201 mAh g-1 at 10 A g-1 over 1000 cycles. This study provided a novel strategy for the development of high-performance carbonaceous materials for SIBs.

Corrosion Engineering To Synthesize Ultrasmall and Monodisperse Alloy Nanoparticles Stabilized in Ultrathin Cobalt (Oxy)hydroxide for Enhanced Electrocatalysis.

Two-dimensional (2D) nanomaterials decorated with ultrasmall and well-alloyed bimetallic nanoparticles (NPs) have many important applications. Developing a facile and scalable 2D material/hybrid synthesis strategy is still a big challenge. Herein, a top-down corrosion strategy is developed to prepare ultrathin cobalt (oxy)hydroxide nanosheets decorated with ultrasmall (∼1.6 nm) alloy NPs. The formation of ultrathin (oxy)hydroxide nanosheets has a restrain effect to prevent the growth of small NPs into bigger ones. Thanks to the ultrathin 2D nature and strong electronic interaction between Co(OH)2 and alloy NPs, the Pt-based binary alloy NPs are greatly stabilized by the Co(OH)2 nanosheets and the hybrids exhibit much enhanced electrocatalytic performance for water splitting. Especially, the mass activities of the PtPd- and PtCu-decorated samples for hydrogen evolution are ∼8 times that of Pt/C. When used as both cathode and anode electrocatalysts to split water, the hybrid nanosheets outperform the commercial Pt/C-RuO2 combination. At 10 mA cm-2, the needed potential is only 1.53 V. This work provides us a highly controllable and scalable means to produce clean 2D nanomaterials decorated with a series of alloy NPs such as PtPd, PtCu, AuNi, and so forth.

MoS2 Nanosheet Arrays Rooted on Hollow rGO Spheres as Bifunctional Hydrogen Evolution Catalyst and Supercapacitor Electrode.

MoS2 has attracted attention as a promising hydrogen evolution reaction (HER) catalyst and a supercapacitor electrode material. However, its catalytic activity and capacitive performance are still hindered by its aggregation and poor intrinsic conductivity. Here, hollow rGO sphere-supported ultrathin MoS2 nanosheet arrays (h-rGO@MoS2) are constructed via a dual-template approach and employed as bifunctional HER catalyst and supercapacitor electrode material. Because of the expanded interlayer spacing in MoS2 nanosheets and more exposed electroactive S-Mo-S edges, the constructed h-rGO@MoS2 architectures exhibit enhanced HER performance. Furthermore, benefiting from the synergistic effect of the improved conductivity and boosted specific surface areas (144.9 m2 g-1, ca. 4.6-times that of pristine MoS2), the h-rGO@MoS2 architecture shows a high specific capacitance (238 F g-1 at a current density of 0.5 A g-1), excellent rate capacitance, and remarkable cycle stability. Our synthesis method may be extended to construct other vertically aligned hollow architectures, which may serve both as efficient HER catalysts and supercapacitor electrodes.

Amperometric nonenzymatic sensing of glucose at very low working potential by using a nanoporous PdAuNi ternary alloy.

The authors present a nonenzymatic sensor for glucose that has an exceedingly low working potential which makes the sensor highly selective over other electroactive species. The sensor is based on the use of a glassy carbon electrode (GCE) that was modified with a nanoporous PdAuNi alloy (np-PdAuNi). The PdAuNi alloy nanostructure displays enhanced electrocatalytic activity for glucose oxidation (compared to PdNi alloys). The modified GCE enables amperometric sensing of glucose at a typical working electrode potential of 0.0 V vs. SCE in solutions of pH 13 containing 0.1 M NaCl. Response is linear in the 5 to 100 µM concentration range, with a 1.7 µM detection limit (at an S/N ratio of 3). For higher concentrations deviations from linearity were found. The method is selective and reproducible. The modified electrode was applied to the determination of glucose in human serum. Graphical Abstract Nanoporous PdAuNi alloy with three-dimensional bicontinuous nanosponge architecture was successfully prepared via chemical dealloying. The electrochemical nonenzymatic glucose sensor shows a low working potential, wide linear range, good sensitivity, low detection limit and excellent selectivity.

Three-Dimensional Binder-Free Nanoarchitectures for Advanced Pseudocapacitors.

The ever-increasing energy demands for electrification of transportation and powering of portable electronics are driving the pursuit of energy-storage technologies beyond the current horizon. Pseudocapacitors have emerged as one of the favored contenders to fill in this technology gap, owing to their potential to deliver both high power and energy densities. The high specific capacitance of pseudocapacitive materials is rooted in the various available oxidation states for fast surface or near-surface redox charge transfer. However, the practical implementation of pseudocapacitors is plagued by the insulating nature of most pseudocapacitive materials. The wealth of the research dedicated to addressing these critical issues has grown exponentially in the past decade. Here, we briefly survey the current progress in the development of pseudocapacitive electrodes with a focus on the discussion of the recent most exciting advances in the design of three-dimensional binder-free nanoarchitectures, including porous metal/graphene-based electrodes, as well as metal-atom/ion-doping-enhanced systems, for advanced supercapacitors with comparable energy density to batteries, and high power density.

Carbon nanotube-reinforced mesoporous hydroxyapatite composites with excellent mechanical and biological properties for bone replacement material application.

Carbon nanotube (CNT)-reinforced mesoporous hydroxyapatite (HA) composites with excellent mechanical and biological properties were fabricated successfully by the in situ chemical deposition of mesoporous HA on homogeneously dispersed CNTs. The CNTs are first synthesized in situ on HA nanopowders by chemical vapor deposition, and then, the HA particles with mesoporous structures are deposited in situ onto the as-grown CNTs by using cetyl trimethyl ammonium bromide as templates to form mesoporous HA encapsulated CNTs (CNT@meso-HA). The modification of CNTs by mesoporous HA leads to strong CNT-HA interfacial bonding, resulting in efficient load transfer between CNT and HA and improved mechanical properties of CNT/HA composites. More importantly, the mesoporous HA structure has a high specific surface area and large surface roughness that greatly promote the cell adhesion and proliferation, resulting in better biocompatibility and improved osteoblast viability (MC3T3-E1) compared to those fabricated by traditional methods. Therefore, the obtained CNT@meso-HA composites are expected to be promising materials for bone regeneration and implantation applications.

Y-junction carbon nanocoils: synthesis by chemical vapor deposition and formation mechanism.

Y-junction carbon nanocoils (Y-CNCs) were synthesized by thermal chemical vapor deposition using Ni catalyst prepared by spray-coating method. According to the emerging morphologies of Y-CNCs, several growth models were advanced to elucidate their formation mechanisms. Regarding the Y-CNCs without metal catalyst in the Y-junctions, fusing of contiguous CNCs and a tip-growth mechanism are considered to be responsible for their formation. However, as for the Y-CNCs with catalyst presence in the Y-junctions, the formation can be ascribed to nanoscale soldering/welding and bottom-growth mechanism. It is found that increasing spray-coating time for catalyst preparation generates agglomerated larger nanoparticles strongly adhering to the substrate, resulting in bottom-growth of CNCs and appearance of the metal catalyst in the Y-junctions. In the contrary case, CNCs catalyzed by isolated smaller nanoparticles develop Y-junctions with an absence of metal catalyst by virtue of weaker adhesion of catalyst with the substrate and tip-growth of CNCs.

Extraordinary Supercapacitor Performance of a Multicomponent and Mixed-Valence Oxyhydroxide.

We report a novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627 F cm(-3) (1097±95 F g(-1) ) at a current density of 0.25 A cm(-3) , originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working-potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working-potential windows gives rise to a high energy density, 51 mWh cm(-3) , of the multicomponent oxyhydroxide-based supercapacitor for high-energy and high-power applications.

Free-standing porous carbon nanofiber/ultrathin graphite hybrid for flexible solid-state supercapacitors.

A micrometer-thin solid-state supercapacitor (SC) was assembled using two pieces of porous carbon nanofibers/ultrathin graphite (pCNFs/G) hybrid films, which were one-step synthesized by chemical vapor deposition using copper foil supported Co catalyst. The continuously ultrathin graphite sheet (∼ 25 nm) is mechanically compliant to support the pCNFs even after etching the copper foil and thus can work as both current collector and support directly with nearly ignorable fraction in a SC stack. The pCNFs are seamlessly grown on the graphite sheet with an ohmic contact between the pCNFs and the graphite sheet. Thus, the accumulated electrons/ions can duly transport from the pCNFs to graphite (current collector), which results in a high rate performance. The maximum energy density and power density based on the whole device are up to 2.4 mWh cm(-3) and 23 W cm(-3), which are even orders higher than those of the most reported electric double-layer capacitors and pseudocapacitors. Moreover, the specific capacitance of the device has 96% retention after 5000 cycles and is nearly constant at various curvatures, suggesting its wide application potential in powering wearable/miniaturized electronics.

Low-temperature solution-processable Ni(OH)2 ultrathin nanosheet/N-graphene nanohybrids for high-performance supercapacitor electrodes.

A novel and facile strategy is developed to fabricate highly nitrogen-doped graphene (N-graphene) based layered, quasi-two-dimensional nanohybrids with ultrathin nanosheet nanocrystals using a low-temperature, solution processing method for high-performance supercapacitor electrodes. High N doping can be achieved together with one of the lowest oxygen content in chemically reduced graphene and related nanohybrids at low temperature by large-scale residue defects of chemically reduced graphene. The layered, quasi-two-dimensional nanohybrids or heterostructures of ultrathin Ni(OH)2 nanosheet nanocrystal/N-graphene can be applied in supercapacitor electrodes with ultrahigh capacitances of ∼1551 F g(-1), excellent rate performance in the scan measurements (from 2 mV s(-1) to 100 mV s(-1)) and in the discharge tests (from 1.5 A g(-1) to 30 A g(-1)) and good cycling stability. Moreover, the capacitance of Ni(OH)2 nanosheet/N-graphene nanohybrids is two and one orders of magnitude higher than that for pure nanocrystals and for the physical mixture of nanocrystal/N-graphene, respectively. Electron transfer in supercapacitor electrodes based on nanohybrids is over 100 times faster than that in electrodes from pure nanocrystals and several tens of times faster than that in electrodes from nanocrystal/N-graphene mixtures. This low-temperature method may provide a low-cost, solution-processable and easily scalable route to high-performance graphene nanohybrid electrodes for energy applications.

Self-grown oxy-hydroxide@ nanoporous metal electrode for high-performance supercapacitors.

A binder-free self-grown oxy-hydroxide@nanoporous Ni-Mn hybrid electrode with high capacitance and cyclic stability is fabricated by electrochemical polarization of a dealloyed nanoporous Ni-Mn alloy. Combined with the low material costs, high electrochemical stability, and environmentally friendly nature, this novel electrode holds great promise for applications in high-capacity commercial supercapacitors.

Achieving highly dispersed nanofibres at high loading in carbon nanofibre-metal composites.

In order to tap into the advantages of the properties of carbon nanotubes (CNTs) or carbon nanofibres (CNFs) in composites, the high dispersion of CNTs (or CNFs) and strong interfacial bonding are the key issues which are still challenging. In the current work, a novel approach, consisting of in situ synthesis of CNFs within the Cu powders and mixing Cu ions with the in situ CNF(Ni/Y)-Cu composite powders in a solvent, was developed to highly disperse CNFs in a Cu matrix. The composite, produced by vacuum hot pressing, shows extremely high strength, 3.6 times more than that of the matrix material alone. It is worth mentioning that this method can disperse CNFs at high loading in a metal matrix, inferring good potential for applications, such as electronic packaging materials.