Electron modulation of cobalt carbonate hydroxide by Mo doping for urea-assisted hydrogen production

Combining urea oxidation reaction(UOR) with hydrogen evolution reaction(HER) is an effective method for energy saving and highly efficient electrocatalytic hydrogen production. Herein, molybdenumincorporated cobalt carbonate hydroxide nanoarrays(CoxMoyCH) are designed and synthesized as a bifunctional catalyst towards UOR and HER. Benefiting from the Mo doping, the dispersed nanoarray structure and redistributed electron density, the CoxMoyCH catalyst display outstanding catalytic performance and durability for both HER and UOR, affording the overpotential of 82 m V for HER and delivering a low potential of the 1.33 V for UOR(vs. reversible hydrogen electrode, RHE) to attain a current density of 10 m A cm^(-2), respectively. Remarkably, when CoxMoyCH was applied as bifunctional catalyst in a twoelectrode electrolyzer, a working voltage of 1.40 V is needed in urea-assisted water electrolysis at10 m A cm^(-2) and without apparent decline for 40 h, outperforming the working voltage of 1.51 V in conventional water electrolysis.

Voltammetric Response and Electrocatalysis of Glasy Carbon Electrode Modified with Monolayer Nickel Hydroxide

The glassy carbon (GC) electrode modified with a monolayer nickel hydroxide (GC/Ni(OH) 2) was prepared by immersion of GC substrate in 1.0×10 -3 mol/L NiSO 4 solution, and then cyclic voltammetric scanning in 0.20 mol/L KOH. Similarly, GC/Co(OH) 2 electrode was prepared too. The experiments showed that the voltammetric behavior of GC/Ni(OH) 2 electrode in 0.20 mol/L KOH is more stable than that of GC/ Co(OH) 2. It was found that the GC/Ni(OH) 2 electrode acts as an effective electrocatalysis for the oxidation of hydrazine.

Chelation-mediated in-situ formation of ultrathin cobalt(oxy)hydroxides on hematite photoanode towards enhanced photoelectrochemical water oxidation

In this work,a facile chelation-mediated route was developed to fabricate ultrathin cobalt(oxy)hydroxides(CoOOH)nanosheets on hematite photoanode(Fe_(2)O_(3)).The route contains two steps of the adsorption of[Co-EDTA]^(2-)species on Fe_(2)O_(3) nanorod array followed by the hydrolysis in alkaline solution.The resulting CoOOH/Fe_(2)O_(3) exhibits a remarkably improved photocurrent density of 2.10 mA cm^(-2) at 1.23 V vs.RHE,which is ca.2.8 times that of bare Fe_(2)O_(3).In addition,a negative shift of onset potential ca.200 mV is achieved.The structural characterizations reveal the chelate EDTA plays important roles that enhance the adsorption of Co species and the formation of contact between CoOOH and Fe_(2)O_(3).(Photo)electrochemical analysis suggests,besides providing active sites for water oxidation,CoOOH at large extent promotes the charge separation and the charge transfer via passivating surface states and suppressing charge recombination.It also found CoOOH possesses some oxygen vacancies,which could act as trapping centers for photogenerated holes and facilitate the charge separation.Intensity modulated photocurrent spectroscopy(IMPS)shows that,under low applied potential the water oxidation mainly occurs on CoOOH,while under high applied potential the water oxidation could occur on both CoOOH and Fe_(2)O_(3).The findings not only provide an efficient strategy for designing ultrathin(oxy)hydroxides on semiconductors for PEC applications but also put forward a new insight on the role of CoOOH during water oxidation.

Synthesis and Characterization of Layered Co_2(OH)_3(CH_3COO)·H_2O

Layered hydroxide metal acetate Co2（OH）3（CH3COO）·H2O with an interlayer spacing of 1.282 nm has been synthesized by a novel method which is employed in ethanol-aqueous mixed solvents media. Experiment results show that the purity of the product by the modified method is higher compared with that by the previous methods. A complete characterization of the as-prepared samples was performed by means of X-ray powder diffraction, IR spectroscopy, scanning electron microscope, as well as magnetic measurement. The facile and effective approach for the preparation of this compound in this study is very interesting and important because it has wide application in the field of anionic exchange reaction for the synthesis of hybrid organic-inorganic compounds.

Unraveling role of double-exchange interaction in electrochemical water oxidation by external magnetic field

Double-exchange(DE) interaction plays an important role in electrocatalytic oxygen evolution reaction(OER).However,precise achievement of DE interaction often requires foreign dopants or vacancy engineering,leading to destabilization of the catalysts and deterioration of performance.By contrast,the utilization of environmentally friendly,contactless,and continuously adjustable magnetic fields to study the OER process is profitable to avoid aforementioned interference factors and further elucidate the direct relationship_(0.5)between DE interaction and OER activity.Here,by using cobalt hydroxide carbonate(Co(OH)(CO_(3))·xH_(2)O,CoHC) nanostructures as a proof-of-concept study,external magnetic fields are carefully implemented to verify the role of DE interaction during water oxidation reaction.Detailed studies reveal that external magnetic fields effectively enhance the reaction rate of the catalyst,the overpotential decreases from 386 to 355 mV(100 mA·cm^(-2)),while Tafel slopes drastically decline from 93 to 67 mV·dec^(-1)(1.0 T).Moreover,magnetic field increment exhibits robust durability.Through in situ Raman and impedance measurements under external field,it can be found that magnetic field promotes the electron migration between Co^(2+) and Co^(3+) in the CoHC catalysts with the assistance of DE interactions,thus boosting the OER efficiency.

Construction of lightweight NiCo-LDH/carbon fiber nanocomposites for broad-band microwave absorption

The rapidly increasing usage of electric technology during the last decades has facilitated the fabrication of high-efficiency microwave absorption(MA)materials(MAMs).In this study,hierarchical NiCo layered double hydroxide(LDH)/carbon fiber(CF)nanocomposites were constructed via simple hydrothermal production,and their MA properties were evaluated.Benefiting from interfacial polarization,defect-induced polarization,and multiple reflections induced by the hierarchical sheets,the LDH/CF composites delivered a better MA perfor-mance than that by pure CF and LDH.The addition ratio of the LDH also played a vital role in determining the impedance matching and microwave absorption performance.Specifically,the optimized LDH/CF composites demonstrated an exceptional reflection loss(RL)of-62.47 dB with a thickness of 2.22 mm,and an effective absorption bandwidth(EAB)covering 6.4 GHz(11.6-18.0 GHz)at a 20 wt.%filling ratio,which outperformed the reported CF-based microwave absorbers.Owing to this superior MA,the as-prepared LDH/CF composites demonstrated to be significantly promising for advancing the usage of CF-based MAMs.

Efficient activation of peroxymonosulfate by hollow cobalt hydroxide for degradation of ibuprofen and theoretical study

Hollow microsphere structure cobalt hydroxide(h-Co(OH)2) was synthesized via an optimized solvothermal-hydrothermal process and applied to activate peroxymonosulfate(PMS) for degradation of a typical pharmaceutically active compound,ibuprofen(IBP).The material characterizations confirmed the presence of the microscale hollow spheres with thin nanosheets shell in h-Co(OH)2,and the crystalline phase was assigned to a-Co(OH)2.h-Co(OH)2 could efficiently activate PMS for radicals production,and 98.6% of IBP was degraded at 10 min.The activation of PMS by h-Co(OH)2 was a pHindependent process,and pH 7 was the optimum condition for the activation-degradation system.Scavenger quenching test indicated that the sulfate radical(SO4^·-) was the primary reactive oxygen species for IBP degradation,which contributed to 75.7%.Fukui index(f^-) based on density functional theory(DFT) calculation predicted the active sites of IBP molecule for SO4^·- attack,and then IBP degradation pathway was proposed by means of intermediates identification and theoretical calculation.The developed hollow Co(OH)2 used to efficiently activate PMS is promising and innovative alternative for organic contaminants removal from water and wastewater.

Vapour-diffusion assisted growth of oriented α-cobalt hydroxide thin films

Layered α-cobalt hydroxides Co（OH1.65 Cl0.35.0.5H2O （1）, Co（OH）1.75（NO3）0.25.0.1H2O（2） with unique macro- and microscale morphologies have been synthesised by a low temperature, ammonia-controlled vapour-diffusion method. The materials have thin film morphologies and were characterized by X-ray powder diffraction （XRD） and field emission scanning electron microscopy （FESEM）.

Controllable magnetic properties of cobalt ferrite particles derived from layered double hydroxide precursors

Cobalt ferrite CoxNi1-xFe2O4 （x = 0, 0.5, 1 ） particles with controllable magnetic properties have been prepared by calcination of co-substituted NiFe^2＋Fe^3＋ -layered double hydroxide （NiFe^2＋Fe^3＋-LDH） precursors prepared via a scalable method involving separate nucleation and aging steps （SNAS）. Their structural and magnetic characteristics were investigated by powder X-ray diffraction （XRD）, scanning electron microscopy （SEM） and vibrating sample magnetometry （VSM）. Measurements of magnetic properties show that the saturation magnetization （Ms） and coercivity （He） of the calcined products increased with increasing cobalt content. The LDH precursor-based product obtained by calcination of a mixture of CoFe^2＋Fe3^＋-LDH and NiFe^2＋Fe^3＋ -LDH powders with a Co/Ni molar ratio of 1：1, exhibits a moderate value of Ms and an increased value of He compared to the corresponding values for an Ni0.5Co0.5Fe2O4 material prepared by calcination of a Co0.5Ni0.5Fe^2＋Fe^3＋-LDH precursor, and a physical mixture of CoFe2O4 and NiFe2O4 with a Co/Ni molar ratio of 1 ： 1. These results may provide a way to regulate magnetic anisotropy of ferrite spinels by varying the composition of the LDH precursors.

Noble-metal-free cobalt hydroxide nanosheets for efficient electrocatalytic oxidation

Cobalt hydroxide has been emerging as a promising catalyst for the electrocatalytic oxidation reactions,including the oxygen evolution reaction(OER)and glucose oxidation reaction(GOR).Herein,we prepared cobalt hydroxide nanoparticles(CoHP)and cobalt hydroxide nanosheets(CoHS)on nickel foam.In the electrocatalytic OER,CoHS shows an overpotential of 306 mV at a current density of 10 mA·cm^-2.This is enhanced as compared with that of CoHP(367 mV at 10 mA·cm^-2).In addition,CoHS also exhibits an improved performance in the electrocatalytic GOR.The improved electrocatalytic performance of CoHS could be due to the higher ability of the two-dimensional nanosheets on CoHS in electron transfer.These results are useful for fabricating efficient catalysts for electrocatalytic oxidation reactions.

Promoting electrocatalytic alcohols oxidation coupled with H_(2) production via ligand intercalation strategy

Electrochemical alcohol oxidation,the alternate of oxygen evolution reaction,has been recognized as an effective way to produce value-added chemicals coupled with H2 production.However,the current researches still suffer from the low reaction rate and Faradaic efficiency(FE)that limits the overall efficiency.Herein,we report a ligand intercalation strategy to enhance the current density of alcohol electrooxidation by intercalating sodium dodecyl sulfonate(SDS)in the interlayer of Co(OH)_(2)catalyst(Co(OH)_(2)-SDS).For instance,the Co(OH)_(2)-SDS shows obviously enhanced current density for glycerol electrooxidation than that of pure Co(OH)_(2).The corresponding glycerol conversion rate and H2 production rate reach 0.35 mmol·cm^(−2)·h^(−1)and 9.1 mL·cm^(−2)·h^(−1)at 1.42 V vs.reversible hydrogen electrode,which are 2.2-and 1.9-fold higher than that of Co(OH)_(2).The yield of formate reaches 86.6%with selectivity of 95.3%at high glycerol conversion of 95.1%(with FE of 83.3%for glycerol oxidation).The Co(OH)_(2)-SDS is demonstrated efficient for different alcohols with enhanced performance.We confirmed that the intercalation of SDS in Co(OH)_(2)can promote the generation and exposure of CoOOH reactive sites,and also facilitate the adsorption of alcohol,thus enabling high reaction rate.

Self-transforming ultrathin α-Co(OH)2 nanosheet arrays from metal-organic framework modified graphene oxide with sandwichlike structure for efficient electrocatalytic oxygen evolution

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction(OER)with high electrochemical activity and durability for diverse renewable and sustainable energy technologies remains challenging.Herein,an ultrasonic-assisted and coordination modulation strategy is developed to construct sandwich-like metal-organic framework(MOF)derived hydroxide nanosheet(NS)arrays/graphene oxide(GO)composite via one-step self-transformation route.Inducing from unsteady state,the dodecahedral ZIF-67 with Co^2+in tetrahedral coordination auto-converts into defect-rich ultrathin layered hydroxides with the interlayered ion NO3-.The self-transforming a-Co(OH)2/GO nanosheet arrays from ZIF-67(Co(OH)2-GNS)change the coordination mode of Co^2+and bring about the exposure of more metal active sites,thereby enhancing the spatial utilization ratio within the framework.As monometal-based electrocatalyst,the optimized Co(OH)2-GNS exhibits remarkable OER catalytic performance evidenced by a low overpotential of 259 mV to achieve a current density of 10 mA·cm-2 in alkaline medium,even exceeding commercial RuO2.During the oxygen evolution process,electron migration can be accelerated by the interfacial/in-plane charge polarization and local electric field,corroborated by the off-axis electron holography.Density functional theory(DFT)calculations further studied the collaboration between ultrathin Co(OH)2 NS and GO,which leads to lower energy barriers of intermediate products and greatly promotes electrocatalytic property.

A two-step approach to synthesis of Co（OH）2/γ-NiOOH/ reduced graphene oxide nanocomposite for high performance supercapacitors

A two-step approach was reported to fabricate cobaltous hydroxide/y- nickel oxide hydroxide/reduced graphene oxide （Co（OH）217-NiOOHIRGO） nanocompo- sites on nickel foam by combining the reduction of graphene oxide with the help of refux condensation and the subsequent hydrothermal of Co（OH）2 on RGO. The microstructural, surface morphology and electrochemical properties of the Co（OH）2/γ-NiOOH/RGO nanocomposite were investigated. The results showed that the surface of the first-step fabricated γ-NiOOH/RGO nanocomposites was uniformly coated by Co（OH）2 nanoflakes with lateral size of tens of nm and thickness of several nm. Co（OH）2/γ-NiOOHIRGO nanocomposite demonstrated a high specific capacitance （745 mF/cm= at 0.5 mAJcm2） and a cycling stability of 69.8% after 1000 cycles at 30 mV/cm2· γ-NiOOH/RGO//Co（OH）2/γ- NiOOH/RGO asymmetric supercapacitor was assembled, and maximum gravimetric energy density of 57.3 W.h/kg and power density of 66.1 kW/kg were achieved. The synergistic effect between the highly conductive graphene and the nanoflake Co（OH）2 structure was responsible for the high electrochemical performance of the hybrid electrode. It is expected that this research could offer a simple method to prepare graphene-based electrode materials.

Phase-transfer synthesis of α-Co(OH)_2 and its conversion to CoO for efficient electrocatalytic water oxidation

Water splitting is an attractive way to produce recyclable hydrogen energy resource. The oxygen evolution reaction(OER) is the rate-determine step of water electrolysis. The exploring of low-cost, highly efficient and durable electrocatalysts for OER is thus extremely important. In this work, we developed a facile two-phase protocol to fabricate an α-Co(OH)_2 using sodium oleate as the phase-transfer surfactant.The crystallinity and structure of the α-Co(OH)_2 was regulated by heat treatments toward enhanced electrocatalytic OER activity. With the calcination of the as-prepared α-Co(OH)_2 at 200 °C, a networked and well-dispersed CoO nanoparticles were formed. The CoO sample afforded an OER current density of 10 mA cm^(-2) under a low overpotential of 312 mV in a 1 mol L^(-1) KOH aqueous solution. The high activity of the CoO material is believed to be associated with its ultra-small particle size and plentiful open spaces in the material, both of which can provide abundant surface catalytic sites.

One-step synthesis of CoSn(OH)_6 nanocubes for high-performance all solid-state flexible supercapacitors

CoSn（OH）6 nanocubes were synthesized by a facile one-step co-precipitate method. Their supercapacitor performances were investigated via a traditional threeelectrode system and all solid-state flexible asymmetric supercapacitor. The electrode shows a maximum specific capacitance up to 695 F·g^-1. The flexible all solid-state asymmetric supercapacitor was fabricated based on CoSn（OH）6 nanocubes and active carbon as positive and negative electrode. The assembled asymmetric supercapacitor exhibits a specific capacitance（97.3 mF·cm^-2）, good rate/mechanical stability and a long cycling stability（5000 cycles）, demonstrating great promise for applications in all solid-state flexible supercapacitors.