In-situ optimizing the valence configuration of vanadium sites in NiV-LDH nanosheet arrays for enhanced hydrogen evolution reaction

Developing the highly active, cost-effective, environmental-friendly, and ultra-stable nonprecious electrocatalysts for hydrogen evolution reaction(HER) is distinctly indispensable for the large-scale practical applications of hydrolytic hydrogen production. Herein, we report the synthesis of well-integrated electrode, NiV layered double hydroxide nanosheet array grown in-situ on porous nickel foam(abbreviated as in-NiV-LDH/NF) via the facile one-step hydrothermal route. Interestingly, the valence configuration of vanadium(V) sites in such NiV-LDH are well dominated by the innovative use of NF as the reducing regulator, achieving the reassembled in-NiV-LDH/NF with a high proportion of trivalent V ions(V3+), and then an enhanced intrinsic electrocatalytic HER activity. The HER testing results show that the in-NiVLDH/NF drives the current densities of 10 and 100 mA cm-2 at extremely low overpotentials of 114 and 245 mV without iR-compensation respectively, even outperforms commercial 20 wt% Pt/C at the large current density of over 80 mA cm-2 in alkaline media, as well as gives robust catalytic durability of at least 100 h in both alkaline and neutral media. More importantly, this work provides a fresh perspective for designing bimetal(oxy) hydroxides electrocatalysts with efficient hydrogen generation.

Controlled WS_(2) crystallinity effectively dominating sodium storage performance

WS2 exhibits tremendous potentials for Na-ions storage owing to high capacity(433 mAh g^(-1)). Nevertheless, WS2 layered structure is often exfoliated with rapid capacity decay and sluggish reaction kinetics.In this work, WS2 nanosheets with different crystallinities are controlled by different synthesis methods.The high crystallinity WS2 exhibits high degree of interlayer order and strong interlayer force. It exhibits superior electrochemical properties, at the current density of 200 mA g^(-1) after 300 cycles with reversible capacity of 471 mAh g^(-1). Even at 5.0 A g^(-1), the capacities can still arrive at 240 mAh g^(-1) after 250 cycles, exhibiting stable cycling performance. Further electrochemical research finds that the high degree of interlayer order of layered WS2 structure can perform highly conducive Na+insertion/extraction with greatly improved contribution of intercalation capacity. Moreover, the strong interlayer force can effectively restrain the exfoliating of the WS2 nanosheets, guaranteeing the stability of the structure. Combining the above result reveals that controlling the order and force of the interlayer is an effective way to enhance the electrochemical properties of WS2 as SIBs anode materials. This work can provide new insight for inhibiting the exfoliation of layered compounds to pursue excellent electrochemical performance in Na-ion storage systems.

Activation of urchin-like Ni-doped W_(18)O_(49)/NF by electrochemical tuning for efficient water splitting

The electrochemical conversion is closely correlated with the electrocatalytic activities of the electrocatalyst.Herein,the urchin-like Ni-doped W_(18)O_(49)/NF with enriched active sites was prepared by solvothermal method followed by a low-temperature pyrolysis treatment was reported.Results demonstrate that the incorporation of Ni-doping triggers the lattice distortion of W_(18)O_(49) for the increasement of oxygen defects.Further,high-valent W^(6+)are partially reduced to low-valent W^(4+),wherein the electrons originate from the oxidation process of Ni^(2+)to Ni^(3+).The Ni^(3+)ions show an enhanced orbital overlap with the OER reaction intermediates.The generated W^(4+)ions contribute to release oxygen vacancies,eventually reorganizing Ni-doped W_(18)O_(49)/NF to unique electrochemical active species with a special amorphous-crystalline interface(AM/NiWO_x/NiOOH/NF).Simultaneously,the reconstruction results in an optimized valence band and conduction band.Eventually,the resultant AM/NiWO_x/NiOOH/NF with abundant active sites and improved oxidation/reduction capability exhibits more superior catalytic performance compared with the Ni-doped W_(18)O_(49)/NF counterpart.This study gives more insights in the electrochemical evolution of the tungsten-based oxide and provides effective strategies for optimizing the catalytic activity of materials with inherent hydrogen evolution reaction limitations.

Facile synthesis of defect-rich Fe-N-C hybrid from fullerene/ferrotetraphenylporphyrin as efficient oxygen reduction electrocatalyst for Zn-air battery

Exploring remarkable oxygen reduction reaction(ORR)electrocatalysts for regenerative fuel cells and metal-air batteries is highly essential.Herein,a novel non-noble metal-based heterogeneous electrocatalyst with rich defects were successfully synthesized by liquid-liquid interfacial precipitation(LLIP)of fullerene(C_(60))and ferrotetraphenylporphyrin(FeTPP)followed by one step pyrolysis.The obtained product annealed at 700℃(C_(60)/FeTPP-700),when employed as ORR electrocatalyst,revealed a positive halfwave potential(E_(1/2))of 0.877 V vs.reversible hydrogen electrode(RHE),which was superior to that of the commercial 25%Pt/C.Delightfully,the assembled Zn-air battery(ZAB)using C_(60)/FeTPP-700 as an air-electrode catalyst exhibited a high power density of 153 m W/cm^(2),specific capacity of 668 mAh/g and long-term cycling stability for more than 250 h.Experimental results proved that the excellent electrocatalytic ORR activity of C_(60)/FeTPP-700 would attribute to the synergistic effect between FeN_xsites,Fe_(3)C/Fe nanoparticles and the structure defects.This work provides a feasible and simple method to prepare nonnoble metal-based ORR electrocatalysts for the application of energy storage and conversion.

Preparation of a SiC/Cristobalite-AlPO_4 Multi-layer Protective Coating on Carbon/Carbon Composites and Resultant Oxidation Kinetics and Mechanism

In order to improve the oxidation resistance of carbon/carbon （C/C） composites,a SiC/C-AlPO4 multi-layer coating was fabricated on the C/C composites by a simple and low-cost method.The internal SiC bonding layer was prepared by a two-step pack cementation process and the external C-AlPO4 coating was deposited by hydrothermal electrophoretic deposition process.Phase compositions and microstructures of the as-prepared multi-layer coating were characterized by X-ray diffraction （XRD）,scaning electron microspocy （SEM） and energy dispersive spectrometer （EDS）.Anti-oxidation properties,oxidation behavior and the failure behavior of the coated composites were investigated.The results indicate that the multi-layer coating exhibits obviously two-layer structure.The inner layer is composed of β-SiC,α-SiC phase with a scale of silicon phase.The outer layer is composed of cristobalite aluminum phosphate （C-AlPO4） crystallites.The SEM observation shows the good bonding between the inner and outer layers.The multi-layer coating displays an excellent oxidation resistance in air in the temperature range from 1573 to 1773 K,and the corresponding oxidation activation energy of the coated C/C composites is calculated to be 117.2 kJ/mol.The oxidation process is predominantly controlled by the diffusion of O2 through the C-AlPO 4 coating.The failure of the multi-layer coating results from the generation of the microholes that may be left by the escape of the oxidation gases.

Phase-mediated cobalt phosphide with unique core-shell architecture serving as efficient and bifunctional electrocatalyst for hydrogen evolution and oxygen reduction reaction

Hydrogen evolution reaction(HER)and oxygen reduction reaction(ORR)have been considered as two critical processes in the field of electrocatalytic water-splitting for hydrogen production and fuel cells.However,the sluggish reaction kinetics of HER and ORR required efficient electrocatalyst such as Pt to promote such process.Transition metal phosphides(TMPs)exhibit great potential to replace noble metal electrocatalysts to accelerate HER and ORR due to their high activity and easy availability.Herein,a highly-efficient bifunctional CoP electrocatalyst for HER and ORR,featuring a unique core-shell structure decorated on nitrogen-doped carbon matrix was designed and constructed via etching a cobalt-based zeolitic imidazolate framework(ZIF-67)with phytic acid(PA)followed by pyrolysis treatment(PA-ZIF-67-900).Experimental results revealed that the pure-phase single-crystalline Co P exhibited outstanding electrocatalytic performance in HER and ORR,superior to Co(PO_(3))_(2) in PA-ZIF-67-700,hybrid phase of Co(PO_(3))_(2) and CoP in PA-ZIF-67-800 and Co_(2)P-doped CoP in PA-ZIF-67-1000.To reach the current density of 10 mA/cm^(2)the as-synthesized Co P required an overpotential of 120 m V for HER in 1 mol/L KOH and half-wave potential of 0.85 V in O_(2)-saturated 0.1 mol/L KOH.This work present new clue for construction of efficient and bifunctional electrocatalyst in the field of energy conversion and storage.

Dual modulation of morphology and electronic structures of VN@C electrocatalyst by W doping for boosting hydrogen evolution reaction

Developing high-efficiency and robust durability electrocatalyst for hydrogen evolution reaction(HER)in water electrolysis functions as a crucial role for the construction of green hydrogen economy,herein,ultrafine W-doped vanadium nitride nanoparticles anchored on N-doped graphitic carbon framework(WVN@NGC)are synthesized through a one-step simple pyrolysis protocol.Owing to the enlarged catalytically active sites,enhanced electrical conductivity and optimized electronic structure,the resultant VN/WN@NGC delivered the prominent HER performance with overpotentials of 143 mV and 158 mV at10 mA/cm^(2) in acid and alkaline media,respectively,accompanied by the long-term stability for at least50 h.This work highlights a novel strategy for a metal-triggered modulation of nitride-based HER electrocatalyst for sustainable energy conversion device.

In Situ Synthesis of Core-Shell Li4Ti5O(12) @ Polyaniline Composites with Enhanced Rate Performance for Lithium-ion Battery Anodes

The core-shell Li4Ti5O（12） @ polyaniline composites（LP） have been synthesized via an in situ synthesis with different mole ratios（25：1, 50：1 and 100：1, aniline：LTO）. As an anode material of lithium-ion batteries,the LP-2 electrodes（50：1） exhibit a high initial reversible capacity of 205 mAh g^（-1）with an initial coulombic efficiency of 97.6% at 0.1 C. Even at a high current density of 10 C, the reversible capacity of the LP-2 electrodes still remains at 102 mAh g^（-1）. Moreover, the LP-2 electrodes retain an impressive high capacity of 161 mAh g^（-1）after 100 cycles at 1 C, with 0.11% capacity fading per cycle. The promising electrochemical performance may be attributed to the significantly decreasing charge-transfer impedance of the LP composite and reductive polarity difference between the cathode and the electrolyte.

Influence and its mechanism of temperature variation in a muffle furnace during calcination on the adsorption performance of rod-like MgO to Congo red

Calcination temperature plays a crucial role in determining the surface properties of generated MgO, but the influence of temperature variation in a muffle furnace during calcination on its performance is rarely reported. Herein we observed that the temperature in a muffle furnace during calcination demonstrated a gradually increasing trend as the location changed from the furnace doorway to the most inner position. The variation in temperature had a great impact on the adsorption performance of generated rod-like MgO without and/or with involvement of Na2SiO3 to Congo red in aqueous solution. To get a better understanding on the detailed reasons, various techniques including actual temperature measurement via multimeter, N2 physical adsorption, CO2 chemical adsorption and FT-IR spectrometry have been employed to probe the correlation between the adsorption performance of generated MgO from various locations and the inner actual temperature of used muffle furnace as well as their physicochemical properties. In addition, two mechanisms were proposed to elucidate the adsorption process of Congo red over the surface of generated MgO without and/or with presence of Na2SiO3, respectively.