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Owing to high theoretical specific capacitance of 3560 F g −1 and intrinsic activity towards oxygen evolution reaction (OER), inexpensive Co 3 O 4 is drawing much attention as either a promising pseudocapacitive electrode or OER catalyst. However, restricted to poor conductivity and lack of active sites, Co 3 O 4 usually exhibits limited experimental capacitance and OER activity, barely satisfying high energy density delivering of supercapacitors and low energy input of water-splitting systems. Herein, we report O 2 2- /O - functionalized oxygen-deficient Co 3 O 4 nanorods for supercapacitor and water splitting dual applications. The CoC 2 O 4 ·2H 2 O converted oxygen-deficient Co 3 O 4 nanorods show enhanced electrical conductivity as confirmed by the increased carrier density. The increased number of Co 2+ sites (oxygen vacancies) and CoOOH are believed to contribute to the improvement in faradaic reactions and OER activity. Additionally, surface functionalization by O 2 2- /O - is realized in oxygen-deficient Co 3 O 4 nanorods. On the basis of these merits, the as-synthesized Co 3 O 4 nanorods demonstrate a significantly high specific capacitance of 739 F g −1 and an ultralow overpotential of 275 mV at 10 mA cm −2 for OER with ultralong stability of over 300 h (@ 100 mA cm −2 ). Specifically, an electrolyzer for overall water splitting can be driven by asymmetric supercapacitors with the optimized cobalt oxide as both electrocatalyst and electrode material. [ABSTRACT FROM AUTHOR]

Transition metal oxalate materials have shown huge competitive advantages for applications in supercapacitors. Herein, nanostructured cobalt oxalate supported on cobalt foils has been facilely fabricated by anodization, and could directly serve as additive/binder-free electrodes for supercapacitors. The as-prepared cobalt oxalate electrodes present superior specific capacitance of 1269 F g −1 at the current density of 6 A g −1 in the galvanostatic charge/discharge test. Moreover, the retained capacitance is as high as 87.2% as the current density increases from 6 A g −1 to 30 A g −1 . More importantly, the specific capacitance of cobalt oxalate retains 91.9% even after super-long cycling of 100,000 cycles. In addition, an asymmetric supercapacitor assembled with cobalt oxalate (positive electrode) and activated carbon (negative electrode) demonstrates excellent capacitive performance with high energy density and power density. [ABSTRACT FROM AUTHOR]

• MnO/Mn 3 O 4 –600 anode was synthesized through a one-step pyrolysis of MOD. • The MnO/Mn 3 O 4 –600 anode shows structure-related performance towards li storage. • The (de)lithiated mechanism of MnO/Mn 3 O 4 –600 was probed by in situ XRD. • The LFP||MnO/Mn 3 O 4 –600 full cell shows outstanding electrochemical performance. Manganese oxides are considered a highly promising anode material in lithium ion batteries (LIBs) because of their high theoretical capacity, abundant sources, relatively low voltage hysteresis, nontoxic and cost-effectiveness. Nevertheless, the practical application of these materials faces many challenges such as poor lifespan and serious volume variation during operation. Herein, MnO/Mn 3 O 4 –600 composite was obtained based on a single-step pyrolysis procedure from commercial manganese(II) oxalate dihydrate (MOD, C 2 H 4 MnO 6). The MnO/Mn 3 O 4 –600 anode exhibits an exceptionally high reversible capacity of 1041.8 mAh g −1 at the current density of 200 mA g −1, and a remarkable lifespan at 1000 mA g −1. The outstanding performance benefits from the formation of porous structures on nanoparticles, which not only mitigate volume changes and prevent the aggregation of internal MnO/Mn 3 O 4 nanoparticles, but also enhance the ion diffusion. The in-depth insights into the (de)lithiated mechanism of the electrode are investigated by in situ X-ray diffraction (XRD) technique. Moreover, when applied in a full cell, the MnO/Mn 3 O 4 –600 anode demonstrates exceptional electrochemical property. The MnO/Mn 3 O 4 –600 was synthesized through a single-step pyrolysis process of commercial manganese(II) oxalate dihydrate. As the anode in LIBs, MnO/Mn 3 O 4 –600 demonstrates excellent performance, which can be attributed to the nanoengineering of MnO/Mn 3 O 4 nanoparticles and the porous architecture. (De)lithiated mechanism was proposed by in situ XRD. Moreover, the LFP||MnO/Mn 3 O 4 –600 full cell exhibits good electrochemical performances. [Display omitted] [ABSTRACT FROM AUTHOR]

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm−2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm−2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm−2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts. A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) was synthesized by a strategy combined rapid solidification with two-step dealloying, in which the total cell voltage of RuNi-1500 NPNWs electrolyzer for water splitting is 1.553 V to deliver a current density of 10 mA cm−2. [Display omitted] • A two-step dealloying strategy was used to prepare RuNi catalysts. • RuNi catalysts exhibit a unique nanoporous nanowires (NPNWs) morphology. • RuNi NPNWs catalysts show excellent electrocatalytic performance for OER and HER. • RuNi NPNWs catalysts can be used as bifunctional catalysts for water splitting. [ABSTRACT FROM AUTHOR]

Alloy-type anodes have attracted extensive attention in magnesium-ion batteries (MIBs) due to their low reaction potentials and high theoretical specific capacities. However, the kinetically sluggish Mg insertion/extraction and diffusion in electrode materials, as well as the huge volume changes resulting in the capacity decay limit their further development. Herein, a series of porous-Bi (P-Bi x) anodes are fabricated through a facile dealloying strategy based on the Sn 100-x Bi x (x = 1, 5, 10, 43, at.%) precursor alloys. Among them, the P–Bi 10 anode delivers a high discharge specific capacity (376.0 mAh g−1 at 500 mA g−1), greatly improved rate capability (363.3 mAh g−1 at 1000 mA g−1) and good cycling stability even at 2000 mA g−1 (104.0 mAh g−1 after 1000 cycles). Furthermore, operando X-ray diffraction (XRD) is performed to unveil the magnesiation/demagnesiation mechanisms of the P–Bi 5 and P–Bi 10 anodes, indicating a simple two-phase reaction process. Additionally, the P–Bi 10 anode displays good compatibility with conventional Mg salt electrolytes such as Mg(TFSI) 2. Our findings could provide useful information on design of high-performance alloy-type anode materials for MIBs. [Display omitted] • P-Bi x anodes were facilely fabricated through dealloying of Sn 100-x Bi x precursors. • The P–Bi 10 shows superior Mg storage performance and compatibility with Mg(TFSI) 2. • Operando XRD unveiled a simple two-phase reaction between Bi and Mg 3 Bi 2. [ABSTRACT FROM AUTHOR]

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni 90 Mo 10 electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm−2, while the Ni 40 Mo 60 electrocatalyst shows an overpotential of 258 mV at 10 mA cm−2 in OER. More significantly, the assembled Ni 40 Mo 60 //Ni 90 Mo 10 electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm−2 for overall water splitting. [Display omitted] • A high throughput method was used to prepare Ni–Mo alloy catalysts. • Ni–Mo alloy catalysts exhibit remarkable activity and stability for HER and OER. • The Ni–Mo alloy acts as a bifunctional catalyst for overall water splitting. • The synergistic effect between Ni and Mo leads to the excellent performances. [ABSTRACT FROM AUTHOR]

Magnetite (Fe 3 O 4) has become a potential anode material in lithium ion batteries (LIBs) because of its high theoretical capacity and low cost, but is impeded for application by its low conductivity and large volume change during cycling. Herein, the Fe 3 O 4 @C-500 composite was fabricated via the one-step pyrolytic carbonization of commercial ammonium ferric citrate (AFC), which is simple and environmentally friendly. As an anode in LIBs, the Fe 3 O 4 @C-500 electrode shows superior specific capacity, long cycling stability and excellent rate performance. Such remarkable performance can be attributed to the formation of the architecture with carbon (C) matrix, not only buffering the volume change and inhibiting the aggregation of internal Fe 3 O 4 nanoparticles during (de)lithiation, but also elevating the electron conductivity. In situ X-ray diffraction (XRD) results demonstrate that the (de)lithiated mechanism of the Fe 3 O 4 @C-500 electrode involves a full electrochemically-driven amorphization upon cycling. Furthermore, the full cell assembled with Fe 3 O 4 @C-500 and LiFePO 4 (LFP) electrodes shows outstanding electrochemical performance, demonstrating its practical energy storage application. [Display omitted] • Fe 3 O 4 @C-500 was fabricated via one-step pyrolytic carbonization of AFC. • Fe 3 O 4 @C-500 delivers good performance by nanoengineering, C matrix and amorphization. • The (de)lithiated mechanism of Fe 3 O 4 @C-500 electrode was probed by in situ XRD. • The full cell presents excellent electrochemical performances. [ABSTRACT FROM AUTHOR]

For lithium ion batteries (LIBs), low electronic conductivity of CuO leads to rapid capacity decay and poor structural stability. Herein, we successfully fabricate three-dimensional CuO nanoflake arrays coated Cu foam by facile and efficient electrochemical oxidation. When being applied as anode material for LIBs, the CuO electrodes deliver stable reversible capacities of 523.9 mA h g −1 at 0.5 A g −1 , 376.1 mA h g −1 at 1.0 A g −1 and 322.7 mA h g −1 at 2.0 A g −1 with high coulombic efficiency (>99%) after 100 cycles. A long cycle life of up to 400 cycles at 2.0 A g −1 is also achieved with the retention capacity of 193.5 mA h g −1 . Moreover, the electrode exhibits excellent rate capability and can regain its original capacities as reversing to the low current densities. Noticeably, on-line differential electrochemical mass spectrometry and in situ Raman measurements confirm the formation of solid electrolyte interface film and the conversion mechanism for the CuO electrodes, respectively. The superior lithium storage performance can be attributed to the favorable nanoflake structures with high surface area and the perfect electrical contact between CuO and Cu substrate. [ABSTRACT FROM AUTHOR]

• 3D Cu current collectors were gained by painting-alloying-dealloying and annealing. • The porous structure of 3D Cu was regulated by altering Ga mass and annealing. • The relationships between porous layer depth and performance were explored. • The Li deposition behaviors on 3D/2D Cu were clarified. Lithium metal anode has shown great potentials for achieving high energy density due to its high theoretical capacity and low redox potential, but its application is impeded by the dendrite proliferation and unstable solid electrolyte interface. Herein, three-dimensional (3D) porous Cu current collectors were fabricated via the combination of painting-alloying-dealloying with subsequent annealing, where the depth and length scale of the porous layer can be facilely regulated by controlling the alloying and annealing processes. In lithium metal batteries, the relationship between the Li deposition behavior and the porous layer depth was explored in detail via electrochemical measurements and ex-situ scanning electron microscopy. Notably, the A-3D Cu-14 current collector with the porous layer depth of around 34.5 µm exhibits long lifespan over 430 h at 1 mA cm−2 and low voltage hysteresis, in comparison with the pristine Cu foil and the porous Cu with thinner porous layers. The superior electrochemical performance of A-3D Cu-14 can be attributed to the enhanced suppression effect upon the Li dendrite deriving from the more accommodation capability of its thick porous layer, as well as the better homogenization of the Li+ ion flux caused by the porous structure. Furthermore, the Li@A-3D Cu-14 | LiFePO 4 full cell shows excellent cycling stability and rate capability in full battery tests. Dealloying-induced modulation upon porous layer depth of three-dimensional copper current collector to stabilize the lithium batteries. [Display omitted] [ABSTRACT FROM AUTHOR]