In Situ Grown Co-Based Interstitial Compounds: Non-3d Metal and Non-Metal Dual Modulation Boosts Alkaline and Acidic Hydrogen Electrocatalysis.

Interfacial engineering and elemental doping are the two parameters to enhance the catalytic behavior of cobalt nitrides for the alkaline hydrogen evolution reaction (HER). However, simultaneously combining these two parameters to improve the HER catalytic properties of cobalt nitrides in alkaline media is rarely reported and also remains challenging in acidic media. Herein, it is demonstrated that high-valence non-3d metal and non-metal integration can simultaneously achieve Co-based nitride/oxide interstitial compound phase boundaries on stainless steel mesh (denoted Mo-Co5.47 N/N-CoO) for efficient HER in alkaline and acidic media. Density functional theory (DFT) calculations show that the unique structure does not only realize multi-active sites, enhanced water dissociation kinetics, and low hydrogen adsorption free energy in alkaline media, but also enhances the positive charge density of hydrogen ions (H+ ) to effectively allow H+ to receive electrons from the catalysts surface toward promoting the HER in acidic media. As a result, the as-prepared Mo-Co5.47 N/N-CoO demands HER overpotential of -28 mV@10 mA cm-2 in an alkaline medium, and superior to the commercial Pt/C at a current density > 44 mA cm-2 in acidic medium. This work paves a useful strategy to design efficient cobalt-based electrocatalysts for HER and beyond.

Phase Evolution on the Hydrogen Adsorption Kinetics of NiFe-Based Heterogeneous Catalysts for Efficient Water Electrolysis.

Transition metal layered double hydroxides, especially nickel-iron layered double hydroxide (NiFe-LDH) shows significant advancement as efficient oxygen evolution reaction (OER) electrocatalyst but also plays a momentous role as a precursor for NiFe-based hydrogen evolution reaction (HER) catalysts. Herein, a simple strategy for developing Ni-Fe-derivative electrocatalysts via phase evolution of NiFe-LDH under controllable annealing temperatures in an argon atmosphere is reported. The optimized catalyst annealed at 340 o C (denoted NiO/FeNi3 ) exhibits superior HER properties with an ultralow overpotential of 16 mV@10 mA cm-2 . Density functional theory simulation and in situ Raman analyses reveal that the excellent HER properties of the NiO/FeNi3 can be attributed to the strong electronic interaction at the interface of the metallic FeNi3 and semiconducting NiO, which optimizes the H2 O and H adsorption energies for efficient HER and OER catalytic processes. This work will provide rational insights into the subsequent development of related HER electrocatalysts and other corresponding compounds via LDH-based precursors.

Surfactant regulated Core-Double-Shell NF@NiO nanosheets matrix as integrated anodes for Lithium-Ion batteries.

The direct oxidation of three-dimensional nickel foam (3D NF) to nickel oxide (NiO) as integrated anode material for lithium-ion batteries (LIBs) has attracted significant attention towards achieving high-areal-capacity and high-energy density LIBs. However, the rate capability of such monolithic NiO in LIBs usually falls off rapidly due to the poor electrical conductivity that hindered its ionic transport kinetics. Herein, to ease the ionic transport constrains, a surfactant-regulated strategy is developed for preparing in-situ core-double-shell architecture that consists of core nickel skeleton, dense nickel oxide shell and porous nickel oxide nanosheets (NS) shell as anode materials for LIBs. Among the three employed surfactants including cationic surfactant, anionic surfactant and nonionic surfactant, the anionic surfactant (sodium dodecyl sulfate, SDS) modulated anode denoted SDS-NF@NiONS exhibits ultrahigh reversible areal capacity of 8.64 mAh cm-2@ 0.4 mA cm-2, and excellent rate areal capacity of 5.20 mAh cm-2 @ 3.0 mA cm-2, which did not only show the best ever reported NiO-based high-areal-capacity based electrodes, but also demonstrate impressive performance in practical full cell LIBs. In addition, in-situ Raman and kinetic analyses confirm the mechanism of Li-ion storage and facile ionic transport kinetics in this proposed design.

Boosting lithium-ion storage performance by ultrafine bimetal carbides nanoparticles coupled with Hollow-like carbon composites.

Metallic carbides demonstrated tremendous application potential in energy conversion field deriving from their distinctive electrochemical activity and chemical stability. Herein, a molybdenum-based hybrid self-template strategy was adopted to confine ultrafine molybdenum carbides and tungsten carbides nanoparticles in N, P-codoped carbon nanotubes (MoC/WC@N, P-CNTs) for enhanced lithium-ion storage. Specifically, hierarchical MoW-polydopamine nanotubes were prepared via a self-template strategy, which employed Mo3O10(C6H8N)2·2H2O nanowires as the template. Ultrafine MoC and WC nanoparticles embedded in ultrathin carbon nanosheets could be obtained rationally after carbonization treatment, which could not only prevent carbides nanoparticles from agglomeration and oxidation, but also endow the rapid electron transfer rate. Thus, MoC/WC@N, P-CNTs displayed outstanding lithium storage abilities with great rate property and long-term cycling durability. The stable specific capacity of 475.0 mAh g-1 could be preserved at high current intensity of 5.0 A g-1 after 1000 cycles, which was one of the best performances for metal carbides anodes. Furthermore, the successful fabrication of lithium-ion hybrid capacitors (LIHCs) delivered the maximum energy density of 117 Wh kg-1 and power density of 6571 W kg-1. Moreover, the superior capacity retention of 89.7 % after 2000 cycles also indicated the excellent cycling stability. The present work highlights a self-template strategy for designing nanostructures toward efficient energy storage and conversion fields.

Melamine-assisted synthesis of porous V2O3/N-doped carbon hollow nanospheres for efficient sodium-ion storage.

Vanadium-based oxides with relatively high theoretical capacity have been regarded as promising electrode materials for boosting energy conversion and storage. However, their poor electrical conductivity usually leads to unsatisfied performance and poor cycling stability. Herein, uniform V2O3/N-doped carbon hollow nanospheres (V2O3/NC HSs) with mesoporous structures were successfully synthesized through a melamine-assisted simple hydrothermal reaction and carbonization treatment. We demonstrated that the introduction of melamine played an essential role in the construction of V2O3/NC HSs. Benefitting from the special mesoporous structure and large specific surface area, the as-obtained sample exhibited enhanced conductivity and structural stability. As a proof of concept, well-defined V2O3/NC HSs exhibited excellent cycling stability and rate performance for sodium-ion batteries, and achieved a discharge capacity of 263.8 mA h g-1 at a current density of 1.0 A g-1 after 1000 cycles, one of the best performances of V-based compounds. The enhanced performance could be attributed to the synergistic effect of the hollow structure and surface carbon coating. The present work describes the design of the morphology and structure of vanadium-based oxides for energy storage devices.

Facile Construction of Metal Phosphides (MP, M = Co, Ni, Fe, and Cu) Wrapped in Three-Dimensional N,P-Codoped Carbon Skeleton toward Highly Efficient Hydrogen Evolution Catalysis and Lithium-Ion Storage.

Transition metal phosphides (TMPs) have been demonstrated for prospective applications in electrocatalytic reaction and energy conversion owing to their specialties of catalytic activity and superhigh theoretical capacity. Herein, a facile and robust strategy for confining phosphides in a three-dimensional N,P-codoped carbon skeleton was achieved through a simple evaporation method. After calcination treatment, metal phosphide nanoparticles (MP, M = Co, Ni, Fe, and Cu) were successfully encapsulated in an interconnected N,P-codoped carbon network, which not only endowed high electrical conductivity and electrochemical stability but also provided more active sites and ion diffusion channels. As-prepared CoP@N,P-C exhibited satisfactory hydrogen evolution reaction activity, displaying lower overpotential of 140 and 197 mV at 10.0 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively. Moreover, CoP@N,P-C also delivered satisfactory lithium-ion storage properties. A higher specific capacity of 604.9 mAh g-1 was retained after 1000 cycles at 0.5 A g-1, one of the best reported performances of CoP-based anode materials. This work highlights a facile pathway to encapsulate metal phosphides in a conductive carbon skeleton, which is suitable for scaled-up production of bifunctional composites for efficient energy storage and conversion.