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.

Model reduction of fractional impedance spectra for time–frequency analysis of batteries, fuel cells, and supercapacitors

Joint time–frequency analysis is an emerging method for interpreting the underlying physics in fuel cells,batteries,and supercapacitors.To increase the reliability of time–frequency analysis,a theoretical correlation between frequency-domain stationary analysis and time-domain transient analysis is urgently required.The present work formularizes a thorough model reduction of fractional impedance spectra for electrochemical energy devices involving not only the model reduction from fractional-order models to integer-order models and from high-to low-order RC circuits but also insight into the evolution of the characteristic time constants during the whole reduction process.The following work has been carried out:(i)the model-reduction theory is addressed for typical Warburg elements and RC circuits based on the continued fraction expansion theory and the response error minimization technique,respectively;(ii)the order effect on the model reduction of typical Warburg elements is quantitatively evaluated by time–frequency analysis;(iii)the results of time–frequency analysis are confirmed to be useful to determine the reduction order in terms of the kinetic information needed to be captured;and(iv)the results of time–frequency analysis are validated for the model reduction of fractional impedance spectra for lithium-ion batteries,supercapacitors,and solid oxide fuel cells.In turn,the numerical validation has demonstrated the powerful function of the joint time–frequency analysis.The thorough model reduction of fractional impedance spectra addressed in the present work not only clarifies the relationship between time-domain transient analysis and frequency-domain stationary analysis but also enhances the reliability of the joint time–frequency analysis for electrochemical energy devices.

Ultra-high specific surface area activated carbon from Taihu cyanobacteria via KOH activation for enhanced methylene blue adsorption

Cyanobacteria-based activated carbon(CBAC)was successfully prepared by pyrolysis-activation of Taihu cyanobacteria.When the impregnation ratio and activated temperature were 2 and 800-C,respectively,the optimal CBACs possessed an ultra-high specific surface(2178.90 m^(2)·g^(-1))and plenty of micro-and meso-pores,as well as a high pore volume(1.01 cm^(3)·g^(-1)).Ascribed to ultra-high surface area,π-π interaction,electrostatic interaction,as well as hydrogen-bonding interactions,the CBACs displayed huge superiority in efficient dye removal.The saturated methylene blue adsorption capacity by CBACs could be as high as 1143.4 mg·g^(-1),superior to that of other reported biomass-activated carbons.The adsorption was endothermic and modeled well by the pseudo-second-order kinetic,intra-particle diffusion,and Langmuir models.This work presented the effectiveness of Taihu cyanobacteria adsorbent ascribed to its super large specific surface area and high adsorption ability.

Capacitive energy storage from single pore to porous electrode identified by frequency response analysis

Rate capability,peak power,and energy density are of vital importance for the capacitive energy storage(CES)of electrochemical energy devices.The frequency response analysis(FRA)is regarded as an efficient tool in studying the CES.In the present work,a bi-scale impedance transmission line model(TLM)is firstly developed for a single pore to a porous electrode.Not only the TLM of the single pore is reparameterized but also the particle packing compactness is defined in the bi-scale.Subsequently,the CES properties are identified by FRA,focused on rate capability vs.characteristic frequency,peak power vs.equivalent series resistance,and energy density vs.low frequency limiting capacitance for a single pore to a porous electrode.Based on these relationships,the CES properties are numerically simulated and theoretically predicted for a single pore to a porous electrode in terms of intra-particle pore length,intra-particle pore diameter,inter-particle pore diameter,electrolyte conductivity,interfacial capacitance&exponent factor,electrode thickness,electrode apparent surface area,and particle packing compactness.Finally,the experimental diagnosis of four supercapacitors(SCs)with different electrode thicknesses is conducted for validating the bi-scale TLM and gaining an insight into the CES properties for a porous electrode to a single pore.The calculating results suggest,to some extent,the inter-particle pore plays a more critical role than the intra-particle pore in the CES properties such as the rate capability and the peak power density for a single pore to a porous electrode.Hence,in order to design a better porous electrode,more attention should be given to the inter-particle pore.

基于多尺度的生物医用高聚物降解强度模型

生物医用高聚物由于其良好的性能与降解性,在医学上有广泛的应用前景。降解过程中的强度变化直接影响到应用情况,而降解过程的复杂性使得强度预测困难。文中在分析强度影响因素的前提下,首先由公式推导证明代表性强度模型的不适用性,然后在生物医用高聚物的降解多尺度模型基础上提出针对降解变化过程中出现的异质相的异相强度模型,不同相采用不同的强度公式,并与多尺度模型耦合计算,计算结果与实验数据拟合得很好,表明文中提出的方法正确可行。

Supported dual-atom catalysts: Preparation, characterization, and potential applications

Developing sustainable and clean electrochemical energy conversion technologies is a crucial step in addressing the challenges of energy shortage and environmental pollution. Exploring and developing new electrocatalysts with excellent performance and low cost will facilitate the commercial use of these energy conversion technologies. Recently, dual-atom catalysts(DACs) have attracted considerable research interest since they exhibit higher metal atom loading and more flexible active sites compared to single-atom catalysts(SACs). In this paper, the latest preparation methods and characterization techniques of DACs are systematically reviewed. The advantages of homonuclear and heteronuclear DACs and the catalytic mechanism and identification technologies between the two DACs are highlighted. The current applications of DACs in the field of electrocatalysis are summarized. The development opportunities and challenges of DACs in the future are prospected. The ultimate goal is to provide new ideas for the preparation of new catalysts with excellent properties by customizing diatomic catalysts for electrochemical applications.

A review of carbon dots and their composite materials for electrochemical energy technologies

Carbon dots(CDs)and their composites as energy storage materials and electrocatalysts have emerged as new types of quasi-zero-dimensional carbon materials.CDs can provide a large specific surface area,numerous electron-electron hole pairs,adjustable heteroatom doping,rich surface functional groups,and so on.However,the roles and functional mechanisms of CDs and their composite materials in the enhancement of electrochemical performance remain unclear and need to be understood in depth.Based on the most recent literature,this paper comprehensively reviews the synthesis methods and applications of various categories of CDs and their composites as electrode materials of supercapacitors,lithium-ion batteries,sodium-ion batteries,and potassium-ion batteries,and as electrocatalysts for hydrogen evolution,oxygen evolution,and oxygen reduction reactions in metal-air batteries,fuel cells,and water electrolysis.To facilitate further research and development,several important aspects related to CDs and their composite materials are summarized with analysis of the technical challenges in practical applications and discussion of the possible development perspectives.

Identifying the Zn-Co binary as a robust bifunctional electrocatalyst in oxygen reduction and evolution reactions via shifting the apexes of the volcano plot

The performance of an electrocatalyst is closely correlated with the binding strength of key oxygencontaining intermediates,i.e.,*OOH,*O and*OH,in the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Facile strategies to achieve favorable binding strength of these oxygen-containing species are urgently demanded,yet it still remains great challenges.Herein,the Zn-Co bimetallic isolation,which serves as an ideal model,is studied systematically by the density functional theory(DFT).Reaction activity volcano plots are built from 48 models,among them the ZnCoN6-gra(I)configuration is confirmed to be the most stable,featured of the strongest interaction with the oxygen-containing species.Optimal △G*O(free energy change of an atomic oxygen containing intermediate)is facilitated,which effectively drifts the volcano peaks of ORR and OER closer to each other,enabling promising bifunctional catalyst.Moreover,the small overpotential in the simulation of protonation and oxidation by hydroxy groups rationalizes the durability of the catalyst in both acid and alkaline media.

Bismuth nanorods confined in hollow carbon structures for high performance sodium-and potassium-ion batteries

Bismuth has drawn widespread attention as a prospective alloying-type anode for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)due to its large volumetric capacity.However,such material encounters drastic particle pulverization and overgrowth of solid-electrolyte interphase(SEI)upon repeated(de)alloying,thus causing poor rate and cycling degradation.Herein,we report a unique structure design with bismuth nanorods confined in hollow N,S-codoped carbon nanotubes(Bi@NS-C)fabricated by a solvothermal method and in-situ thermal reduction.Ex-situ SEM observations confirm that such a design can significantly suppress the size fining of Bi nanorods,thus inhibiting the particle pulverization and repeated SEI growth upon charging/discharging.The as achieved Bi@NS-C demonstrates outstanding rate capability for SIBs(96.5%capacity retention at 30 A g^(-1) vs.1 A g^(-1)),and a record high rate performance for PIBs(399.5 m Ah g^(-1)@20 A g^(-1)).Notably,the as constructed full cell(Na_(3)V_(2)(PO_(4))_(3)@C|Bi@NS-C)demonstrates impressive performance with a high energy density of 219.8 W h kg^(-1) and a high-power density of 6443.3 W kg^(-1)(based on the total mass of active materials on both electrodes),outperforming the state-of-the-art literature.

A comprehensive modification enables the high rate capability of P2-Na_(0.75)Mn_(0.67)Ni_(0.33)O_(2) for sodium-ion cathode materials

The Na^(+)/vacancy ordering can effectively affect the electrochemical behavior of P2-type cathode material.In this work we proposed an integrated strategy by attaining a high Na content,In^(3+) doping in conjunction with NaInO_(2) coating in the P2-Na_(0.75)Mn_(0.67)Ni_(0.33)O_(2) which can inhibit the sodium vacancy order,smooth the electrochemical curve,and enhance the structural stability and rate capability.A combination of X-ray diffraction analysis and DFT calculation indicate that the In(3+) ions in the Na layer serve as"pillars”to stabilize the layered structure,especially for high current density charging.The P2-Na_(0.75)Mn_(0.67)Ni_(0.33)In_(0.02)O_(2) with an impressive sodium content exhibits a remarkable reversible capacity of 109.6 mAh g^(-1),superior rate capability capacity of 79.8 mAh g^(-1)at 20 C,and 85%capacity retention after 100 cycles at 5 C.This work demonstrates an efficient approach for the comprehensive optimization of sodium ion cathode materials.

Fast and extensive intercalation chemistry in Wadsley-Roth phase based high-capacity electrodes

Wadsley-Roth (W-R) structured oxides featured with wide channels represent one of the most promising material families showing compelling rate performance for lithium-ion batteries.Herein,we report an indepth study on the fast and extensive intercalation chemistry of phosphorus stabilized W-R phase PNb_(9)O_(25) and its application in high energy and fast-charging devices.We explore the intercalation geometry of PNb_(9)O_(25) and identify two geometrical types of stable insertion sites with the total amount much higher than conventional intercalation-type electrodes.We reveal the ion transportation kinetics that the Li ions initially diffuse along the open type Ⅲ channels and then penetrate to edge sites with low kinetic barriers.During the lithiation,no remarkable phase transition is detected with nearly intact host phosphorous niobium oxide backbone.Therefore,the oxide framework of PNb_(9)O_(25) keeps almost unchanged with all the fast diffusion channels and insertion cavities well-maintained upon cycling,which accomplishes the unconventional electrochemical performance of W-R structured electrodes.

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.

Self assembled electron blocking and lithiophilic interface towards dendrite-free solid-state lithium battery

The poor interfacial contact is one of the biggest challenges that solid-state lithium batteries suffer from.Reducing the solid-state electrolyte surface energy by transforming the interface from lithiophobic to lithiophilic is effective to promote the interfacial contact, but electronic conductive interphases usually increase the risk of electron attack, thus leading to uncontrollable Li dendrite growth. Herein, we propose a self-assembled thermodynamic stable Li I interphase to simultaneously improve the interfacial contact between the garnet electrolyte Li_7La_(3)Zr_(2)O_(12)(LLZO) and Li anode, and prohibit the electron attack. The direct contact between LLZO and Li and the high temperature Li melting process was ascribed to Zr4+reduction, which facilitated Li dendrite formation and propagation. With the modification of the high lithiophilic I_(2) thin film, the area specific interfacial resistance of LLZO/Li was reduced from 1525 Ω/cm^(2) to 57 Ω/cm^(2). More importantly, LLZO was protected from being reduced due to the outstanding electronic insulativity of the Li I interphase, which leaded to a high critical current density of 1.2/7.0 m A/cm^(2) in the time/capacity-constant modes, respectively.

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.

A water-stable high-voltage P3-type cathode for sodium-ion batteries

The Na-deficient P3-type layered oxide cathode material usually experience complex in-plane Na^(+)/vacancy ordering rearrangement and undesirable P3-O3 phase transitions in the high-voltage region,leading to inferior cycling performance.Additionally,they exhibit unsatisfactory stability when exposed to water for extended periods.To address these challenges,we propose a Cu/Ti co-doped P3-type cathode material(Na_(0.67)Ni_(0.3)Cu_(0.03)Mn_(0.6)Ti_(0.07)O_(2)),which effectively mitigates Na^(+)/vacancy ordering and suppresses P3-O3 phase transitions at high voltages.As a result,the as-prepared sample exhibited outstanding cyclic performance,with 81.9%retention after 500 cycles within 2.5–4.15 V,and 75.7%retention after300 cycles within 2.5–4.25 V.Meanwhile,it demonstrates enhanced Na^(+)transport kinetics during desodiation/sodiation and reduced growth of charge transfer impedance(R_(ct))after various cycles.Furthermore,the sample showed superb stability against water,exhibiting no discernible degradation in structure,morphology,or electrochemical performance.This co-doping strategy provides new insights for innovative and prospective cathode materials.

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.

Bimetallic site substitution of NiCoP nanoneedles as bifunctional electrocatalyst for boosted water splitting

The bimetallic nickel-cobalt phosphide (NiCoP) has been confirmed as an efficient electrocatalyst in water splitting. But little attention is paid to the selectivity and affinity of metal sites on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a trace-Zn-doping (2.18 wt.%) NiCoP (Zn-NiCoP) whereby the nanoparticles self-aggregated to form elongated nanoneedles. We discover that both Co and Ni sites can be replaced by Zn. The Co substitution improves HER, while the Ni substitution dramatically reduces the energy barrier of the rate-determining step (*O → *OOH). The negative shift of d-band centers after Zn doping ameliorates the intermediate desorption. Therefore, Zn-NiCoP demonstrates superior electrocatalytic activity with overpotentials of 48 and 240 mV for HER and OER at 10 and 50 mA·cm^(−2), respectively. The cell voltage with Zn-NiCoP as both anode and cathode in water splitting was as low as 1.35 V at 10 mA·cm^(−2).

Insight into the influence of ether and ester electrolytes on the sodium-ion transportation kinetics for hard carbon

The electrochemical performance of hard carbon(HC)materials is closely related to the electrolyte used in the sodium ion batteries(SIBs).Conventional electrolytes carbonate(EC)demonstrates low initial Columbic efficiency(ICE)and poor rate performance,which is one of the main bottlenecks that limits the practical application of HCs.Ether electrolyte(diglyme)was reported to improve the rate performance of HCs.Nevertheless,the underlying mechanism for the excellent rate capability is still lack of in-depth study.In this work,the differences of sodium-ion diffusion between ether and carbonate-base electrolytes in HCs are analyzed layer by layer.Firstly,when sodium-ions are diffused in electrolyte,the diffusion coefficient of sodium-ion in ether electrolyte is about 2.5 times higher than that in ester electrolytes by molecular dynamics(MD)simulation and experimental characterization.Furthermore,when the solvated sodium-ions are diffused into the solid electrolyte interphase(SEI)interface and the HCs material,the enhanced charge transfer kinetics(thin SEI layer(4.6 vs.12 nm)and low RSEI(1.5 vs.24Ω))at the SEI combined with low desolvation energy(0.248 eV)are responsible for high-rate performance and good cycling stability of HC in ether electrolyte.Therefore,high diffusion coefficient,low desolvation energy,and good interface are the intrinsic reasons for enhanced rate performance in ether electrolyte,which also has guiding significance for the design of other high-rate electrolytes.

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.

Comparsion analysis of data mining models applied to clinical research in Traditional Chinese Medicine

OBJECTIVE: To help researchers selecting appropriate data mining models to provide better evidence for the clinical practice of Traditional Chinese Medicine(TCM) diagnosis and therapy.METHODS: Clinical issues based on data mining models were comprehensively summarized from four significant elements of the clinical studies:symptoms, symptom patterns, herbs, and efficacy.Existing problems were further generalized to determine the relevant factors of the performance of data mining models, e.g. data type, samples, parameters, variable labels. Combining these relevant factors, the TCM clinical data features were compared with regards to statistical characters and informatics properties. Data models were compared simultaneously from the view of applied conditions and suitable scopes.RESULTS: The main application problems were the inconsistent data type and the small samples for the used data mining models, which caused the inappropriate results, even the mistake results. These features, i.e. advantages, disadvantages, satisfied data types, tasks of data mining, and the TCM issues, were summarized and compared.CONCLUSION: By aiming at the special features of different data mining models, the clinical doctors could select the suitable data mining models to resolve the TCM problem.