钴钒水滑石纳米片用于电催化尿素氧化

电解水是一种常用的制氢方法,但高能耗的阳极析氧反应(OER)阻碍了其应用。尿素氧化反应(UOR)具有较低的热力学电势,是最有前景的OER替代反应之一。过渡金属基水滑石具有独特的层状结构和层间阴离子可交换等优点,被认为是性能优异的UOR催化剂,然而目前大多数研究主要聚焦于后过渡金属元素。该研究通过一步法制备了具有前/后过渡金属的CoV-LDHs纳米片。与相同方法制备的Co(OH)_(2)相比,CoV-LDHs纳米片具有以下优点:1)纳米片结构有利于暴露更多的活性位点。2)V的引入增强了CoV-LDHs的亲水性,提高了其本征电催化动力学。3)Co(3d^(7)4s^(2))和V(3d^(3)4s^(2))之间的d-电子补偿效应有利于促进尿素的吸附。因此,CoV-LDHs仅需要1.52 V(vs.RHE)就可以达到10 mA·cm^(−2)的电流密度,比Co(OH)_(2)低了70 mV,同时CoV-LDHs较低的塔菲尔斜率表明了其较快的反应动力学。此外,CoV-LDHs在连续反应10 h后,驱动电位几乎没有增加,表明其具有良好的稳定性。该研究结果不仅证明了前/后过渡金属之间的d-电子补偿效应可以提高UOR催化性能,还为设计高效的UOR催化剂提供了可行的途径。

Electrodeposited 3D hierarchical NiFe microflowers assembled from nanosheets robust for the selective electrooxidation of furfuryl alcohol

A robust and green strategy for the selective upgrading of biomass-derived platform chemicals towards highly valuable products is important for the sustainable development.Herein,the efficient electrocatalytic oxidation of biomass-derived furfuryl alcohol(FFA)into furoic acid(FurAc)catalyzed by the electrodeposited non-precious NiFe microflowers was successfully reached under the low temperature and ambient pressure.The 3D hierarchical NiFe microflowers assembled from ultrathin nanosheets were controllably synthesized by the electrodeposition method and uniformly grown on carbon fiber paper(CFP).Electrochemical analysis confirmed that NiFe nanosheets more preferred in the selective oxidation of FFA(FFAOR)than oxygen evolution reaction(OER).The linear sweep voltammetry(LSV)in FFAOR displayed a clear decrease towards lower potential,resulting in 30 mV reduction of overpotential at 20 mA cm^(-2) compared with that of OER.The optimal catalyst Ni_(1)Fe_(2) nanosheets exhibited the highest selectivity of FurAc(94.0%)and 81.4%conversion of FFA within 3 h.Besides,the influence of various reaction parameters on FFAOR was then explored in details.After that,the reaction pathway was investigated and rationally proposed.The outstanding performance for FFAOR can be ascribed to the unique structure of 3D flower-like NiFe nanosheets and oxygen vacancies,resulting in large exposure of active sites,faster electron transfer and enhanced adsorption of reactants.Our findings highlight a facile and convenient mean with a promising green future,which is promising for processing of various biomass-derived platform chemicals into value-added products.

Efficient electrooxidation of biomass-derived aldehydes over ultrathin Ni V-layered double hydroxides films

Selective upgrading of C=O bonds to afford carboxylic acid is significant for the petrochemical industry and biomass utilization.Here we declared the efficient electrooxidation of biomass-derived aldehydes family over NiV-layered double hydroxides(LDHs) thin films.Mechanistic studies confirmed the hydroxyl active intermediate(-OH*) generated on the surface of NiV-LDHs films by employing electrochemical impedance spectroscopy and the electron paramagnetic resonance spectroscopy.By using advanced techniques,e.g.,extended X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy,NiV-LDHs films with 2.6 nm could expose larger specific surface area.Taking benzaldehyde as a model,high current density of 200 mA cm^(-2)at 1.8 V vs.RHE,81.1% conversion,77.6% yield of benzoic acid and 90.8% Faradaic efficiency were reached,which was superior to most of previous studies.Theoretical DFT analysis was well matched with experimental findings and documented that NiV-LDHs had high adsorption capacity for the aldehydes to suppress the side reaction,and the aldehydes were oxidized by the electrophilic hydroxyl radicals formed on NiV-LDHs.Our findings offer a universal strategy for the robust upgrading of diverse biomass-derived platform chemicals.

Green fabrication of nickel-iron layered double hydroxides nanosheets efficient for the enhanced capacitive performance

Rational synthesis of robust layered double hydroxides(LDHs) nanosheets for high-energy supercapacitors is full of challenges.Herein,we reported an ultrasonication-assisted strategy to eco-friendly fabricate NiFe-LDHs nanosheets for the enhanced capacitive behavior.The experimental results combined with different advanced characterization tools document that the utilization of ultrasonication has a profound effect on the morphology and thickness of the as-obtained NiFe-LDHs,alternatively affecting the capacitive behavior.It shows that NiFe-LDHs nanosheets prepared with 2-h ultrasonic treatments display the exceptional capacitive performance because of the synergetic effect of ultrathin thickness,large specific surface area,and high mesoporous volume.The maximum specific capacitance of Ni_(3) Fe_(1)-LDHs nanosheets with the thickness of 7.39 nm and the specific surface area of 77.16 m~2 g^(-1) reached 1923 F g^(-1),which is competitive with most previously reported values.In addition,the maximum specific energy of the assembled NiFe-LDHs//AC asymmetric supercapacitor achieved 49.13 Wh kg^(-1) at400 W kg^(-1).This work provides a green technology to fabricate LDHs nanosheets,and offers deep insights for understanding the relationship between the morphology/structure and capacitive behavior of LDHs nanosheets,which is helpful for achieving high-performance LDHs-based electrode materials.

Fe nanoclusters anchored in biomass waste-derived porous carbon nanosheets for high-performance supercapacitor

Metal-nanocluster materials have gradually become a promising electrode candidate for supercapaci-tor application.The high-efficient and rational architecture of these metal-nanocluster electrode mate-rials with satisfied supercapacitive performance are full of challenges.Herein,Fe-nanocluster anchored porous carbon(FAPC)nanosheets were constructed through a facile and low-cost impregnation-activation strategy.Various characterization methods documented that FAPC nanosheets possessed a mesopore-dominated structure with large surface area and abundant Fe-N4 active sites,which are crucial for su-percapacitive energy storage.The optimal FAPC electrode exhibited a high specific capacitance of 378 F/g at a specific current of 1 A/g and an excellent rate capability(271 F/g at 10 A/g),which are comparable or even superior to that of most reported carbon candidates.Furthermore,the FAPC-based device achieved a desired specific energy of 14.8 Wh/kg at a specific power of 700 W/kg.This work opens a new avenue to design metal-nanocluster materials for high-performance biomass waste-based supercapacitors.

Temperature-controlled fabrication of hydrophilic manganese oxide microspheres as high-performance electrode materials for supercapacitors

The supercapacitive properties of manganese oxides(MnO_(x))are strongly affected by their crystal structure.Nevertheless,the relationship between the crystal structure and supercapacitive performance of Mn O_(x)is elusive.Herein,a temperature-controlled fabrication method was developed to achieve MnO_(2),Mn_(3)O_(4),MnO and Mn_(2)O_(3)microspheres with various crystal structure as electrode materials tunable for supercapacitors.The detailed material and electrochemical characterizations revealed the structureactivity relationship of Mn O_(x)microspheres by systematically investigating the effect of valence state,specific surface area,conductivity and morphology on supercapacitive performance.Among these MnO_(x)materials,nanoneedle-like Mn O_(2)delivered a relatively high specific capacitance of 274.1 F/g at 1 A/g due to a high Mn valence state of+4,a large specific surface area of 113.4 m^(2)/g and a desirable electronic conductivity of 1.73×10^(-5)S/cm.Furthermore,MnO_(2)presented a remarkable cycle stability with 115%capacitance retention after 10,000 cycles owing to the enhancement of wettability.This work not only provides a facile strategy to modulate MnO_(x)crystal structure,but also offers a deep understanding of structure-dependent supercapacitive performance of MnO_(x).

One-step architecture of bifunctional petal-like oxygen-deficient NiAl-LDHs nanosheets for high-performance hybrid supercapacitors and urea oxidation

Nickel-based layered double hydroxides(LDHs)are promising electrode materials in the fields of energy storage(supercapacitors)and conversion(urea oxidation).The rational construction of atomic and electronic structure is crucial for nickel-based LDHs to realize their satisfactory electrochemical performance.Herein,we report a facile,ecofriendly,one-step synthesis process to construct petal-like oxygen-deficient NiAl-LDH nanosheets for hybrid supercapacitors(HSCs)and urea oxidation reaction(UOR).The asprepared NiAl-LDH nanosheets with rich oxygen vacancies possess a large specific surface area of 216.6 m2 g^(-1) and a desirable electronic conductivity of 3.45×10^(–4)S cm^(-1) to deliver an ultra-high specific capacitance of 2801 F g^(-1)(700 C g^(-1))at 1 A g^(-1).Furthermore,high specific energy of 50.0 W h kg^(-1) at 400 W kg^(-1) and excellent cycle stability with 91%capacitance retention after 10,000 cycles are achieved by the NiAl-LDHs/CFP(carbon fiber paper)(+)//YP-80F(a commercial activated carbon)(–)HSC.Besides,NiAl-LDH nanosheets also work as an efficient electrocatalyst for UOR,which only requires 1.42 V vs.reversible hydrogen electrode to drive 10 mA cm^(–2) in 1 mol L^(-1) KOH with 0.33 mol L^(-1) urea.This remarkable performance is superior to most reported values of previous candidates owing to the thin structure of NiAl-LDH nanosheets for exposing more active sites and abundant oxygen vacancies.In addition,various reaction parameters are investigated to optimize the electrochemical performance.In general,this work paves a new way for the architecture of multifunctional nanostructured energy materials.

In situ growth of hydrophilic nickel-cobalt layered double hydroxides nanosheets on biomass waste-derived porous carbon for high-performance hybrid supercapacitors

Rational design and cost-effective fabrication of layered double hydroxides(LDHs)nanosheets with extraordinary electrochemical performance is a key challenge for hybrid supercapacitors(HSCs).Herein,we report a facile in situ growth methodology to eco-friendly synthesize hydrophilic Ni Co-LDHs nanosheets on biomass waste-derived porous carbon(BC)for robust high-performance HSC cathode.The in situ growth process under ultrasonication realizes the rational arrangement of Ni Co-LDHs nanosheets on the surface of BC,which effectively increases the specific surface area,promotes the electronic conductivity and enhances the wettability of Ni Co-LDHs nanosheets without affecting their thickness values.With the beneficial effects of ultrathin thickness of LDHs nanosheets(6.20 nm),large specific surface area(2324.1 m^(2)g^(-1)),low charge transfer resistance(1.65Ω),and high wettability with electrolyte(34°–35°),the obtained Ni2Co1-LDHs/BC50 electrode possesses an ultra-high specific capacitance of 2390 F g^(-1)(956 C g^(-1))at 1 A g^(-1),which is superior to most reported values.Furthermore,an assembled Ni_(2)Co_(1)-LDHs/BC50//YP-80F HSC delivers a maximum specific energy of 52.47 Wh kg^(-1)at375 W kg^(-1),and maintains a high capacitance retention of 75.9%even after 4000 cycles.This work provides a facile approach to fabricate LDHs nanosheets based cathode materials for high-performance HSCs.