Fe稳固的FeOOH@NiOOH电催化剂的大电流极化设计与析氧研究

电解水技术是制取高纯度氢气的有效途径,为传统的氢气生产提供了一种可持续的替代方案.其中,开发性能优异的电催化材料是降低电解水制氢成本的关键.析氧反应(OER)由于涉及多个电子转移而导致的动力学缓慢,是克服高过电位的主要挑战.镍铁羟基/氢氧化物(NiFe(oxy)hydroxides)是近期研究的热点,其在碱性条件下具有极低的OER过电位,部分材料性能甚至超过了贵金属基催化剂,如IrO_(2)和RuO_(2).然而,NiFe(oxy)hydroxides的长期催化稳定性,尤其是在大电流下的长期催化稳定性,成为限制其实际应用的主要问题,这主要是由于铁元素的严重流失导致的.因此,如何有效控制和利用电化学溶解/沉积动力学成为稳定铁位点的关键.为克服该挑战,本文提出了一种大电流极化重构方法来固定活性铁位点.通过在大电流(1.5 A cm^(-2))下对材料进行表面快速极化重构,成功制备了FeOOH@NiOOH(eFNO_(L))电催化剂.eFNO_(L)不仅具有稳定的铁位点,还暴露出高指数晶面,因此eFNO_(L)同时展现出较好的OER催化活性和稳定性.同时,密度泛函理论计算结果表明,与具有低指数晶面的FeNiOOH相比,大电流极化工程制备的分相eFNO_(L)对铁位点表现出更高的结合能,可以有效抑制OER过程中的铁流失,且高指数晶面在改变速率决定步骤和减少吸附能垒上具有更大的优势.电化学测试结果表明,经过优化后的eFNO_(L)催化剂在产生100和500 mA cm^(-2)大电流密度仅需234和27 mV的过电位,并且具有较小的Tafel斜率(35.2 mV dec^(-1)).由于铁位点结合能的提高,eFNO_(L)催化剂在500 mA cm^(-2)的电流密度下能够稳定催化超过100 h,且仅有1.5%的性能衰减,优于近期报道的大多数镍铁基OER催化剂.综上,本文为开发高活性和高稳定性能的催化剂提供了一种有效的大电流电化学重构策略,在电解水制氢领域实现其工业化的大规模应用方面显示出巨大潜力,有望降低可持续电解水制氢成本.

Molten salt synthesis of porous carbon and its application in supercapacitors: A review

Carbon materials have taken an important role in supercapacitor applications due to their outstanding features of large surface area,low price,and stable physicochemical properties.Considerable research efforts have been devoted to the development of novel synthesis strategy for the preparation of porous carbon materials in recent years.In particular,molten salt strategy represents an emerging and promising method,whereby it has shown great potential in achieving tailored production of porous carbon.It has been proved that the molten salt-assisted production of carbon via the direct carbonization of carbonaceous precursors is an effective approach.Furthermore,with the incorporation of electrochemical technology,molten salt synthesis of porous carbon has become flexible and diversiform.Here,this review focuses on the mainstream molten salt synthesis strategies for the production of porous carbon materials,which includes direct molten salt carbonization process,capture and electrochemical conversion of CO_(2)to value-added carbon,electrochemical exfoliation of graphite to graphene-based materials,and electrochemical etching of carbides to new-type carbide-derived carbon materials.The reaction mechanisms and recent advances for these strategies are reviewed and discussed systematically.The morphological and structural properties and capacitive performances of the obtained carbon materials are summarized to reveal their appealing points for supercapacitor applications.Moreover,the opportunities and challenges of the molten salt synthesis strategy for the preparation of carbon materials are also discussed in this review to provide inspiration to the future researches.

Continuous electrodeposition of silicon and germanium micro/nanowires from their oxides precursors in molten salt

In recent years,silicon(Si)and germanium(Ge)materials have been considered as promising highperformance anode materials for lithium-ion batteries due to their high theoretical capacities.It is of great importance to design and synthesize micro/nanostructured Si and Ge materials.In this work,we demonstrated that Si,Ge and SiGe micro/nanowires can be continuously synthesized from their oxides precursors through molten salt electrodeposition.The electrochemical synthesis processes have been investigated systematically,and the deposited Si,Ge and SiGe micro/nanowires have been characterized and compared.The results show that the micro/nanostructured Si and Ge materials with tunable morphology can be facilely and continuously produced via molten salt electrodeposition.The electrodeposition process generally includes calcium oxide-assisted dissolution and electrodeposition processes,and the morphologies of the deposited Si and Ge products can be controlled by varying conditions.Si micro/nanowires,Si films,Ge micro/nanowires,and Ge particles can be continuously synthesized in a controlled manner.

An integrated strategy towards the facile synthesis of core-shell SiC-derived carbon@N-doped carbon for high-performance supercapacitors

Porous active core-shell carbon material with excellent synergistic effect has been regarded as a prospective material for supercapacitors.Herein,we report an integrated method for the facile synthesis of carbide-derived carbon(CDC)encapsulated with porous N-doped carbon(CDC@NC)towards highperformance supercapacitors.Polydopamine(PDA)as nitrogen and carbon sources was simply coated on SiC nanospheres to form SiC@PDA,which was then directly transformed into CDC@NC via a onestep molten salt electro-etching/in-situ doping process.The synthesized CDC@NC with hierarchically porous structure has a high specific surface area of 1191 m^(2) g^(-1).The CDC core and NC shell are typical amorphous carbon and more ordered N-doped carbon,respectively.Benefitting from its unique dual porous structures,the CDC@NC demonstrates high specific capacitances of 255 and 193 F g^(-1) at 0.5 and20 A g^(-1),respectively.The reaction mechanism of the electro-etching/in-situ doping process has also been investigated through experimental characterizations and theoretical density functional theory calculations.It is suggested that the molten salt electro-etching/in-situ doping strategy is promising for the synthesis of active core-shell porous carbon materials with synergistic properties for supercapacitors without the need for additional doping/activation processes.

Electrolysis of Converter Matte in Molten CaCl₂-NaCl

The electrolytic production of nickel-copper alloy by electrochemical reduction of converter matte in molten salt has been investigated. The sintered solid porous pellets of Ni3S2, Cu2S and converter matte were electrolyzed at a voltage of 3.0 V in molten CaCl2-NaCl under the protection of argon gas at 700℃, respectively. The electro-reduction processes were investigated and the products were characterized. The results show that the molten salt electro-reduction process can be used to produce nickel, copper and nickel-copper alloy directly from Ni3S2, Cu2S and converter matte precursors in molten CaCl2-NaCl, respectively. CaS would be formed as the intermediate compound during the electro-reduction process, and then the formed CaS can be gradually decomposed and removed with the increase of the electrolysis time. The experimental results show that the molten salt electro-reduction process has the potential to be used for the reduction of sulfide minerals in molten CaCl2-NaCl.

Highly efficient and stable electrocatalyst for hydrogen evolution by molybdenum doped Ni-Co phosphide nanoneedles at high current density

There is an increasingly urgent need to develop cost-effective electrocatalysts with high catalytic activity and stability as alternatives to the traditional Pt/C in catalysts in water electrolysis.In this study,microspheres composed of Mo-doped NiCoP nanoneedles supported on nickel foam were prepared to address this challenge.The results show that the nanoneedles provide sufficient active sites for efficient electron transfer;the small-sized effect and the micro-scale roughness enhance the entry of reactants and the release of hydrogen bubbles;the Mo doping effectively improves the electrocatalytic performance of NiCoP in alkaline media.The catalyst exhibits low hydrogen evolution overpotentials of 38.5 and 217.5 mV at a current density of 10 mA·cm^(-2) and high current density of 500 mA·cm^(-2),respectively,and only 1.978 V is required to achieve a current density of 1000 mA·cm^(-2) for overall water splitting.Density functional theory(DFT)calculations show that the improved hydrogen evolution performance can be explained as a result of the Mo doping,which serves to reduce the interaction between NiCoP and intermediates,optimize the Gibbs free energy of hydrogen adsorption(△G_(*H)),and accelerate the desorption rate of *OH.This study provides a promising solution to the ongoing challenge of designing efficient electrocatalysts for high-current-density hydrogen production.

Suppression of multistep phase transitions of O3-type cathode for sodium-ion batteries

O3-type layered oxide cathodes have been widely investigated due to their high reversible capacities and sufficient Na+reservoirs.However,such materials usually suffer from complex multistep phase transitions along with drastic volume changes,leading to the unsatisfied cycle performance.Herein,we report a Mg/Ti co-doped O3-type NaNi_(0.5)Mn_(0.5)O_(2),which can effectively suppress the complex multistep phase transition and realize a solid-solution reaction within a wide voltage range.It is confirmed that,the Mg/Ti co-doping is beneficial to enhance the structural stability and integrity by absorbing micro-strain and distortions.Thus,the as obtained sample delivers an outstanding cyclic performance(82.3%after 200 cycles at 1 C)in the voltage range of 2.0-4.0 V,and a high discharge capacity of 86.6 mAh/g after 100 cycles within the wide voltage range(2.0-4.5 V),which outperform the existing literatures.This co-doping strategy offers new insights into high performance O3-type cathode for sodium ion batteries.

Construction of Cu-Zn Co-doped layered materials for sodium-ion batteries with high cycle stability

Due to its high operational voltage and energy density,P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) has become a leading cathode material for sodium-ion batteries(SIBs),which is an ideal option for large-scale energy storage.However,the practical application of P2-type Na_(0.67)Ni_(0.3)Mn_(0.7)O_(2) is limited by the capacity constraints and unwanted phase transitions,presenting significant challenges to the widespread application of SIBs.To address these challenges and optimize the electrochemical properties of the P2 phase cathode material,this study proposes a Cu and Zn co-doped strategy to improve the electrochemical performance.The incorporation of Cu/Zn can stabilize the P2-phase structure against P2-O2 phase transitions,thus enhancing its electrochemical properties.The as-obtained P2-type Na0.67[Ni_(0.3)Mn_(0.58)Cu_(0.09)Zn_(0.03)]O_(2) cathode material shows an impressive cycling stability,maintaining 80%capacity retention after 1000 cycles at 2 C.The cyclic voltammetry(CV)tests show that the Cu^(2+)/Cu^(3+)redox reaction is also involved in charge compensation during the charge/discharge process.

Recent Advances in Electrochemical-Based Silicon Production Technologies with Reduced Carbon Emission

Sustainable and low-carbon-emission silicon production is currently one of the main focuses for the metallurgical and materials science communities.Electrochemistry,considered a promising strategy,has been explored to produce silicon due to prominent advantages:(a)high electricity utilization efficiency;(b)low-cost silica as a raw material;and(c)tunable morphologies and structures,including films,nanowires,and nanotubes.This review begins with a summary of early research on the extraction of silicon by electrochemistry.Emphasis has been placed on the electro-deoxidation and dissolution–electrodeposition of silica in chloride molten salts since the 21st century,including the basic reaction mechanisms,the fabrication of photoactive Si films for solar cells,the design and production of nanoSi and various silicon components for energy conversion,as well as storage applications.Besides,the feasibility of silicon electrodeposition in room-temperature ionic liquids and its unique opportunities are evaluated.On this basis,the challenges and future research directions for silicon electrochemical production strategies are proposed and discussed,which are essential to achieve large-scale sustainable production of silicon by electrochemistry.

Free-standing SnNb_(2)O_(6)@CSN film as flexible anode for high performance sodium-ion batteries

Free-standing electrodes are promising candidates for flexible rechargeable batteries, toward the application of flexible energy storage devices, due to their merits of additive-free, lightweight, and high energy density. Herein, we report a free-standing SnNb_(2)O_(6)@CSN flexible film with SnNb_(2)O_(6) encapsulated in 3D carbon skeleton nanofibers by electrospinning and carbonization processes as flexible anode for sodium-ion batteries(SIBs). The 3D carbon skeleton nanofibers serve as ion/electron transport pathway to improve the electrochemical reaction kinetics and meanwhile alleviate the volume changes of SnNb_(2)O_(6) during charge-discharge processes. The as-constructed half-cell(SnNb_(2)O_(6)@CSN‖Na) exhibits excellent cycling stability of 99.2 m Ah/g at 0.5 A/g after 950 cycles(coulombic efficiency of ~100%) and a high rate performance of 108.6 mAh/g at 10 A/g. In addition, the pouch cell can light up the LEDs at different bending angles(0°, 90°, 180°). This research shows a promising anode material for flexible energy storage electronics.

Wafer-Scale Synthesis of WS_(2)Films with In Situ Controllable p-Type Doping by Atomic Layer Deposition

Wafer-scale synthesis of p-type TMD films is critical for its commercialization in next-generation electro/optoelectronics.In this work,wafer-scale intrinsic n-type WS_(2)films and in situ Nb-doped p-type WS_(2)films were synthesized through atomic layer deposition(ALD)on 8-inchα-Al_(2)O_(3)/Si wafers,2-inch sapphire,and 1 cm^(2)GaN substrate pieces.The Nb doping concentration was precisely controlled by altering cycle number of Nb precursor and activated by postannealing.WS_(2)n-FETs and Nb-doped p-FETs with different Nb concentrations have been fabricated using CMOS-compatible processes.X-ray photoelectron spectroscopy,Raman spectroscopy,and Hall measurements confirmed the effective substitutional doping with Nb.The on/off ratio and electron mobility of WS_(2)n-FET are as high as 105 and 6.85 cm^(2)V^(-1)s^(-1),respectively.In WS_(2)p-FET with 15-cycle Nb doping,the on/off ratio and hole mobility are 10 and 0.016 cm^(2)V^(-1)s^(-1),respectively.The p-n structure based on n-and p-type WS_(2)films was proved with a 10^(4)rectifying ratio.The realization of controllable in situ Nb-doped WS_(2)films paved a way for fabricating wafer-scale complementary WS_(2)FETs.

Wafer-Scale Synthesis of WS_(2) Films with In Situ Controllable p-Type Doping by Atomic Layer Deposition

Wafer-scale synthesis of p-type TMD films is critical for its commercialization in next-generation electro/optoelectronics.In this work,wafer-scale intrinsic n-type WS_(2)films and in situ Nb-doped p-type WS_(2)films were synthesized through atomic layer deposition(ALD)on 8-inchα-Al_(2)O_(3)/Si wafers,2-inch sapphire,and 1 cm^(2)GaN substrate pieces.The Nb doping concentration was precisely controlled by altering cycle number of Nb precursor and activated by postannealing.WS_(2)n-FETs and Nb-doped p-FETs with different Nb concentrations have been fabricated using CMOS-compatible processes.X-ray photoelectron spectroscopy,Raman spectroscopy,and Hall measurements confirmed the effective substitutional doping with Nb.The on/off ratio and electron mobility of WS_(2)n-FET are as high as 105 and 6.85 cm^(2)V^(-1)s^(-1),respectively.In WS_(2)p-FET with 15-cycle Nb doping,the on/off ratio and hole mobility are 10 and 0.016 cm^(2)V^(-1)s^(-1),respectively.The p-n structure based on n-and p-type WS_(2)films was proved with a 10^(4) rectifying ratio.The realization of controllable in situ Nb-doped WS_(2)films paved a way for fabricating wafer-scale complementary WS_(2)FETs.