Developing efficient and stable non‐noble electrocatalysts for the oxygen evolution reaction (OER) remains challenging for practical applications. While nickel–iron layered double hydroxides ...(NiFe‐LDH) are emerging as prominent candidates with promising OER activity, their catalytic performance is still restricted by the limited active sites, poor conductivity and durability. Herein, hierarchical nickel–iron–cobalt LDH nanosheets/carbon fibers (NiFeCo‐LDH/CF) are synthesized through solvent‐thermal treatment of ZIF‐67/CF. Extended X‐ray adsorption fine structure analyses reveal that the Co substitution can stabilize the Fe local coordination environment and facilitate the π‐symmetry bonding orbital in NiFeCo‐LDH/CF, thus modifying the electronic structures. Coupling with the structural advantages, including the largely exposed active surface sites and facilitated charge transfer pathway ensured by CF, the resultant NiFeCo‐LDH/CF exhibits excellent OER activity with an overpotential of 249 mV at 10 mA cm−1 as well as robust stability over 20 h.
Hierarchical nanostructures fabricated from edge‐rich nickel–iron–cobalt layered double hydroxides (NiFeCo‐LDH) nanosheets and carbon fiber are synthesized by solvent‐thermal treatment of ZIF‐67/CF. Owing to the synergistic interaction between the three metal ions, largely exposed active surface sites and tunable electronic structure in LDH materials, NiFeCo‐LDH/CF displays superior oxygen evolution reaction performance and robust stability.
Developing high-performance electrocatalysts for hydrogen evolution reaction (HER) is crucial for sustainable hydrogen production, yet still challenging. Here, we report boron-modulated osmium (B-Os) ...aerogels with rich defects and ultra-fine diameter as a pH-universal HER electrocatalyst. The catalyst shows the small overpotentials of 12, 19, and 33 mV at a current density of 10 mA cm
in acidic, alkaline, and neutral electrolytes, respectively, as well as excellent stability, surpassing commercial Pt/C. Operando X-ray absorption spectroscopy shows that interventional interstitial B atoms can optimize the electron structure of B-Os aerogels and stabilize Os as active sites in an electron-deficient state under realistic working conditions, and simultaneously reveals the HER catalytic mechanisms of B-Os aerogels in pH-universal electrolytes. The density functional theory calculations also indicate introducing B atoms can tailor the electronic structure of Os, resulting in the reduced water dissociation energy and the improved adsorption/desorption behavior of hydrogen, which synergistically accelerate HER.
Two‐dimensional (2D) metal–organic framework nanosheets (MOF NSs) play a vital role in catalysis, but the most preparation is ultrasonication or solvothermal. Herein, a liquid–liquid interfacial ...synthesis method has been developed for the efficient fabrication of a series of 2D Ni MOF NSs. The active sites could be modulated by readily tuning the ratios of metal precursors and organic linkers (RM/L). The Ni MOF NSs display highly RM/L dependent activities towards 2e oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2), where the Ni MOF NSs with the RM/L of 6 exhibit the optimal near‐zero overpotential, ca. 98 % H2O2 selectivity and production rate of ca. 80 mmol gcat−1 h−1 in 0.1 M KOH. As evidenced by X‐ray absorption fine structure spectroscopy, the coordination environment of active sites changed from saturation to unsaturation, and the partially unsaturated metal atoms are crucial to create optimal sites for enhancing the electrocatalysis.
2D Ni metal–organic framework nanosheets (MOF NSs) with controlled coordination mode were carefully created through a liquid‐liquid interfacial synthesis strategy for the first time and adopted as efficient electrocatalysts for hydrogen peroxide (H2O2) synthesis. The optimized partially unsaturated Ni MOF NSs‐6 exhibits near‐zero overpotential as well as ca. 98 % H2O2 selectivity in 0.1 M KOH, exceeding most electrocatalysts up to date.
A copper sulfide (CuS) nanowire (NW) array with a hierarchical nanoarchitecture is directly fabricated on copper foil using a simple and cost-effective liquid-solid reaction. The morphology and ...microstructure of CuS NW arrays are systematically investigated by scanning electron microscopy, X-ray diffraction spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrochemical results obtained at various polarization cut-offs and scan rates reveal that the CuS NW array shows highly reversible features and favorable rate abilities. Most importantly, the excellent specific capacitance that is achieved in CuS NW nanoelectrodes is as high as 305 F g−1, which is one of the high value reported CuS-based pseudocapacitors. An energy density of 70.8 Wh kg−1 is obtained at a current density of 2mAcm−2. The CuS NW nanoelectrode has superior cycling stability with 87% retention of initial specific capacitance after 5000 cycles.
Li‐ion hybrid supercapacitors (LHSCs) are intensely studied due to their favorable power densities. However, combined higher energy density materials, particularly anodes, are desirably sought. ...Herein, a defect‐dominating structure protocol is reported. Specifically, two visible structural defects, i.e., crystal vacancy and lattice distortion have been introduced in situ in ultrafine niobium nitride (NbN) monocrystals that are integrated into a carbon (C) framework. Highly reversible Li‐ion storage capacities up to 540 mAh g−1 are demonstrated in such a NbN@C composite anode, together with excellent rate capability and cycling stability. An extra vacancy‐induced capacity contribution of the defective NbN component is evidenced by first‐principles density functional theory (DFT) simulations in contrast to perfect modeling. Coupling with an activated carbon (AC) cathode, the NbN@C//AC cell can deliver balanced energy and power densities of 53.8 Wh kg−1 and 7818 W kg−1 at 4 A g−1, and retain a desired energy density of 56.1 Wh kg−1 after 10 000 cycles at 1 A g−1. Findings from this study, particularly the demonstrated defects‐induced extra capacity of pseudocapacitive materials, may inspire new structural material designs of LHSCs.
Lattice flaws and nano‐engineering are excellent strategies for increasing the favourable space for lithium ion insertion and extraction in electrode materials. This study incorporates defects and vacancies into the pseudocapacitance material NbN, resulting in an ultra‐small nanoparticle carbon composite with exceptional electrochemical performance.
Designing efficient bifunctional electrocatalysts with excellent activity and robust stability presents a central challenge for the large‐scale commercialization of water electrolysis. Herein, a ...facile approach is reported for the construct of atomically thin amorphous RuM (MCo, Fe, or Ni) bimetallenes as high‐performance electrocatalysts toward both electrochemical hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The RuCo bimetallene manifests excellent bifunctional activity characterized by low required overpotentials, superior price activity, robust electrochemical durability as well as a low cell potential water splitting performance, outperforming Pt/C and RuO2 benchmark catalysts. Combined operando X‐ray absorption spectroscopy investigation and theoretical simulations reveal the synergism taking place between binary constituents, in which Co serves a promotive role along the HER/OER reaction pathway, contributing via optimal binding to *OH for facile water dissociation as well as modulating the Ru electronic structure favorably, hence rendering high activity catalytic centers for both the alkaline HER and OER.
Integrating oxophilic Co into Ru amorphous bimetallene realizes excellent bifunctional hydrogen evolution reaction and oxygen evolution reaction catalytic activity in an alkaline medium. Operando X‐ray absorption spectroscopy and theoretical studies reveal an energy‐favorable synergistic mechanism taking place on the electrocatalytic surface, in which Co functions as a promoter, enhancing the water adsorption and dissociation and optimizing the electron configuration of Ru sites, boosting the catalytic activity.
Abstract
A single-crystalline ZnGa
2
O
4
epilayer was successfully grown on c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition. This epilayer was used as a ternary oxide ...semiconductor for application in high-performance metal–semiconductor–metal photoconductive deep-ultraviolet (DUV) photodetectors (PDs). At a bias of 5 V, the annealed ZnGa
2
O
4
PDs showed better performance with a considerably low dark current of 1 pA, a responsivity of 86.3 A/W, cut-off wavelength of 280 nm, and a high DUV-to-visible discrimination ratio of approximately 10
7
upon exposure to 230 nm DUV illumination than that of as-grown ZnGa
2
O
4
PDs. The as-grown PDs presented a dark current of 0.5 mA, a responsivity of 2782 A/W at 230 nm, and a photo-to-dark current contrast ratio of approximately one order. The rise time of annealed PDs was 0.5 s, and the relatively quick decay time was 0.7 s. The present results demonstrate that annealing process can reduce the oxygen vacancy defects and be potentially applied in ZnGa
2
O
4
film-based DUV PD devices, which have been rarely reported in previous studies.
Efficient glycerol electrooxidation reaction (GEOR) over gold@nickel sulfide (Au@NiSx) yolk@shell nanostructures is demonstrated, achieving ≈50.4% glycerol conversion at 10 h, 92.6% selectivity ...toward three‐carbon products, and 90.7% total Faradaic efficiency. By regulating the electrode potential, tartronic acid (TART), one of the highest value‐added intermediates, can be produced with a selectivity as high as 43.1% and a yield of 45.6 µmol cm−2 h−1. A combination of ex situ microstructural analysis, operando Raman, and operando X‐ray absorption measurements reveals a dynamic surface reconstruction course from Au@NiSx to Au@NiSx/NiOOH during the glycerol oxidation process. The unique reconstructed architectures featuring conductive interior NiSx components and active surface high‐valence Ni3+ species account for the superior GEOR performance. Further integration of GEOR with hydrogen evolution reaction is realized by employing Au@NiSx as both anode and cathode electrocatalysts in a two‐electrode configuration. Concomitantly production of TART and hydrogen fuel is accomplished. This study demonstrates that Au@NiSx not only can convert glycerol to TART with remarkable efficiency and selectivity, but also can produce hydrogen at a moderate level. The findings from this study can facilitate the development of dual‐functional electrocatalysts capable of producing high‐value products at both the cathode and anode sides.
Practical use of gold@nickel sulfide (Au@NiSx) yolk@shell nanostructures for efficient glycerol electrooxidation (GEOR) is demonstrated. The unique re‐constructed architectures featuring conductive interior NiSx component and active surface high‐valence Ni3+ species accounted for the superior GEOR performance. Further integration of GEOR with hydrogen evolution reaction is realized by employing Au@NiSx as both anode and cathode electrocatalysts in a two‐electrode configuration.
A simple one‐step electroplating route is proposed for the synthesis of novel iron oxyhydroxide lepidocrocite (γ‐FeOOH) nanosheet anodes with distinct layered channels, and the microstructural ...influence on the pseudocapacitive performance of the obtained γ‐FeOOH nanosheets is investigated via in situ X‐ray absorption spectroscopy (XAS) and electrochemical measurement. The in situ XAS results regarding charge storage mechanisms of electrodeposited γ‐FeOOH nanosheets show that a Li+ can reversibly insert/desert into/from the 2D channels between the FeO6 octahedral subunits depending on the applied potential. This process charge compensates the Fe2+/Fe3+ redox transition upon charging–discharging and thus contributes to an ideal pseudocapacitive behavior of the γ‐FeOOH electrode. Electrochemical results indicate that the γ‐FeOOH nanosheet shows the outstanding pseudocapacitive performance, which achieves the extraordinary power density of 9000 W kg−1 with good rate performance. Most importantly, the asymmetric supercapacitors with excellent electrochemical performance are further realized by using 2D MnO2 and γ‐FeOOH nanosheets as cathode and anode materials, respectively. The obtained device can be cycled reversibly at a maximum cell voltage of 1.85 V in a mild aqueous electrolyte, further delivering a maximum power density of 16 000 W kg−1 at an energy density of 37.4 Wh kg−1.
The simplified architecture and the sole use of iron oxyhydroxide lepidocrocite (γ‐FeOOH) nanosheet anodes leads to a new class of entirely charge storage devices exhibiting the extraordinary power density of 9000 W kg−1 with good rate performance. Notably, a maximum power density of 16 000 W kg−1 at an energy density of 37.4 Wh kg−1 is performed through MnO2 NS‐CC//FeOOH NS‐CC hybrid supercapacitors.
Anode-free lithium metal batteries (AF-LMBs) can deliver the maximum energy density. However, achieving AF-LMBs with a long lifespan remains challenging because of the poor reversibility of Li+ ...plating/stripping on the anode. Here, coupled with a fluorine-containing electrolyte, we introduce a cathode pre-lithiation strategy to extend the lifespan of AF-LMBs. The AF-LMB is constructed with Li-rich Li2Ni0.5Mn1.5O4 cathodes as a Li-ion extender; the Li2Ni0.5Mn1.5O4 can deliver a large amount of Li+ in the initial charging process to offset the continuous Li+ consumption, which benefits the cycling performance without sacrificing energy density. Moreover, the cathode pre-lithiation design has been practically and precisely regulated using engineering methods (Li-metal contact and pre-lithiation Li-biphenyl immersion). Benefiting from the highly reversible Li metal on the Cu anode and Li2Ni0.5Mn1.5O4 cathode, the further fabricated anode-free pouch cells achieve 350 W h kg−1 energy density and 97% capacity retention after 50 cycles.
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