Highly Reversible Zn Metal Anodes Enabled by Increased Nucleation Overpotential

Dendrite formation severely compromises further development of zinc ion batteries. Increasing the nucleation overpotential plays a crucial role in achieving uniform deposition of metal ions. However, this strategy has not yet attracted enough attention from researchers to our knowledge. Here, we propose that thermodynamic nucleation overpotential of Zn deposition can be boosted through complexing agent and select sodium L-tartrate(Na-L) as example. Theoretical and experimental characterization reveals L-tartrate anion can partially replace H_(2)O in the solvation sheath of Zn^(2+), increasing de-solvation energy. Concurrently, the Na^(+) could absorb on the surface of Zn anode preferentially to inhibit the deposition of Zn^(2+) aggregation. In consequence, the overpotential of Zn deposition could increase from 32.2 to 45.1 mV with the help of Na-L. The Zn-Zn cell could achieve a Zn utilization rate of 80% at areal capacity of 20 mAh cm^(-2). Zn-LiMn_(2)O_(4) full cell with Na-L additive delivers improved stability than that with blank electrolyte. This study also provides insight into the regulation of nucleation overpotential to achieve homogeneous Zn deposition.

Active straining engineering on self-assembled stacked Ni-based hybrid electrode for ultra-low overpotential

Generating sufficient strains on metal surfaces are highly challenging owing to that most metals can deform plastically to relax the strains on the surfaces.In this work,we developed a facile but highly efficient stacked deposition strategy to in situ activation and reconstruction of NiO/NiOOH on Ni matrix,following with the migration of Fe ions to NiOOH.The Fe sites on the Ni/NiO/NiOOH facilitate the formation of the stable*OH oxygenated intermediates,and the Ni matrix in the catalyst provides the catalyst excellent stability.The oxygen evolution reaction(OER)performance of the stacked NiFe-5 with compressive strain displays the strengthened binding to oxygenated intermediates and superior OER activity,the ultralow overpotentials of 162 versus reversible hydrogen electrode at 10 mA cm^(-2).On the other hand,the Ni-5 without the incorporation of Fe has shown an outstanding hydrogen evolution reaction(HER)activity,affording an overpotential of 47 mV at 10 mA cm^(-2).The NiFe-5‖Ni-5 enables the overall water splitting at a voltage of 1.508 V to achieve 20 mA cm^(-2) with remarkable durability.The stacked deposition strategy improves binding strength of Ni-based catalysts to oxygenated intermediates via generating compressive strain,causing high catalytic activities on OER and HER.

Confining Li_(2)O_(2) in tortuous pores of mesoporous cathodes to facilitate low charge overpotentials for Li-O_(2) batteries

Achieving low charge overpotentials represents one of the most critical challenges for pursuing highperformance lithium-oxygen(Li-O_(2))batteries.Herein,we propose a strategy to realize low charge overpotentials by confining the growth of lithium peroxide(Li_(2)O_(2))inside mesoporous channels of cathodes(CMK-8).The CMK-8 cathode with tortuous pore structures can extend the diffusion distance of lithium superoxide(LiO_(2))in the mesoporous channels,facilitating the further reduction of LiO_(2) to lithium peroxide(Li_(2)O_(2))inside the pores and preventing them to be diffused out of the pores.Therefore,Li_(2)O_(2) is trapped in the mesoporous channels of CMK-8 cathodes,ensuring a good Li_(2)O_(2)/CMK-8 contact interface.The CMK-8 electrode exhibits a low charge overpotential of 0.43 V and a good cycle life for 72 cycles with a fixed capacity of 500 m Ah g^(-1) at 0.1 A g^(-1).This study proposes a strategy to achieve a low charge overpotential by confining Li_(2)O_(2) growth in the mesoporous channels of cathodes.

Regulating surface electron structure of PtNi nanoalloy via boron doping for high‐current‐density Li‐O2 batteries with low overpotential and long‐life cyclability

The realization of high‐efficiency,reversible,stable,and safe Li‐O2 batteries is severely hindered by the large overpotential and side reactions,especially at high rate conditions.Therefore,rational design of cathode catalysts with high activity and stability is crucial to overcome the terrible issues at high current density.Herein,we report a surface engineering strategy to adjust the surface electron structure of boron(B)‐doped PtNi nanoalloy on carbon nanotubes(PtNiB@CNTs)as an efficient bifunctional cathodic catalyst for high‐rate and long‐life Li‐O2 batteries.Notably,the Li‐O2 batteries assembled with as‐prepared PtNiB@CNT catalyst exhibit ultrahigh discharge capacity of 20510 mA·h/g and extremely low overpotential of 0.48 V at a high current density of 1000 mA/g,both of which outperform the most reported Pt‐based catalysts recently.Meanwhile,our Li‐O2 batteries offer excellent rate capability and ultra‐long cycling life of up to 210 cycles at 1000 mA/g under a fixed capacity of 1000 mA·h/g,which is two times longer than those of Pt@CNTs and PtNi@CNTs.Furthermore,it is revealed that surface engineering of PtNi nanoalloy via B doping can efficiently tailor the electron structure of nanoalloy and optimize the adsorption of oxygen species,consequently delivering excellent Li‐O2 battery performance.Therefore,this strategy of regulating the nanoalloy by doping nonmetallic elements will pave an avenue for the design of high‐performance catalysts for metal‐oxygen batteries.

The influence of stress-dependent overpotential on dendrite growth in all-solid-state battery with cracks

Dendrite growth is one of the main challenges in maintaining the service life of all-solid-state lithium-ion batteries.Mechanical stress has been reported to significantly affect dendrite growth.In this study,to explain the effect of mechanical stress on electrochemical reactions in all-solid-state batteries,a modified phase-field model for dendrite growth is proposed by considering the stress-dependent overpotential.Dendrite growth under different mechanical loadings in an all-solid-state battery is investigated using the proposed model.Consistent with previous experimental results,the current result shows that compressive stress inhibits dendrite growth.Considering the stress concentration at the tips of processing-induced microcracks,the effects of the number and distribution of microcracks on dendrite growth are investigated.The results show that the stress-concentration field induced at the tips of cracks or voids can change the morphology of dendrites and decrease their growth rates.This study provides a new perspective for explaining Li dendrite growth under mechanical stress and offers inspiration for prolonging the service life of all-solid-state batteries based on defect and stress regulation,which may be further realized in experiments by filling solid electrolytes with different types of nanofillers.

Photo-assisted decoration of Ag-Pt nanoparticles on Si photocathodes for reducing overpotential toward enhanced photoelectrochemical water splitting

Developing new catalysts to decorate photoelectrodes has been widely used to enhance the performance of photoelectrochemical(PEC)cells.However,the high cost,complex synthesis,and poor stability of catalyst decoration strongly hinder its practical application.Here,we report a facile and low-cost decoration of Ag-Pt nanoparticles(Ag-Pt NPs)on Si photocathodes with TiO_(2)/Ti sacrificial overlayers.Such a decoration does not rely on any metallic-ion precursor solution since it is formed automatically via galvanic replacement reactions during PEC measurements;that is,Ti is displaced by Ag^(+)and Pt^(2+)ions,which are from the employed reference and counter electrodes,respectively.The as-decorated Ag-Pt NPs are verified to significantly enhance the hydrogen evolution reduction kinetics without substantially degrading the optical performance of Si photocathodes.Owing to optoelectronic advantages,the overpotential required to maintain a photocurrent density of 10 mA cm(under AM1.5 G illumination)is reduced from-0.8 V_(RHE)(for the bare planar Si photocathode)to-0.1 V_(RHE)(for the planar Si photocathode with Ag-Pt NP decoration).Moreover,a further anodic shift(to 0 V_(RHE))is visible for the Si nanowire array photocathode with Ag-Pt NP decoration,along with high long-term stability of the PEC response in acidic and neutral electrolytes.This study opens a new opportunity for the photo-assisted decoration of various alloy NPs on the morphology-varying photoelectrodes with different applications.

Industrial-current-density CO_(2)-to-formate conversion with low overpotentials enabled by disorder-engineered metal sites

CO_(2)electroreduction to formate is technically feasible and economically viable,but still suffers from low selectivity and high overpotential at industrial current densities.Here,lattice-distorted metallic nanosheets with disorder-engineered metal sites are designed for industrial-current-density CO_(2)-to-formate conversion at low overpotentials.As a prototype,richly lattice-distorted bismuth nanosheets are first constructed,where abundant disorder-engineered Bi sites could be observed by high-angle annular dark-field scanning transmission electron microscopy image.In-situ Fourier-transform infrared spectra reveal the CO_(2)•−*group is the key intermediate,while theoretical calculations suggest the electron-enriched Bi sites could effectively lower the CO_(2)activation energy barrier by stabilizing the CO_(2)•−*intermediate,further affirmed by the decreased formation energy from 0.49 to 0.39 eV.As a result,the richly lattice-distorted Bi nanosheets exhibit the ultrahigh current density of 800 mA·cm^(−2)with 91%Faradaic efficiencies for CO_(2)-to-formate electroreduction,and the formate selectivity can reach nearly 100%at the current density of 200 mA·cm^(−2)with a very low overpotential of ca.570 mV,outperforming most reported metal-based electrocatalysts.

Ligand centered electrocatalytic efficient CO_(2) reduction reaction at low overpotential on single-atom Ni regulated molecular catalyst

Electrochemical CO_(2) reduction reaction(CO_(2)RR)into value-added chemicals/fuels is crucial for realizing the sustainable carbon cycle while mitigating the energy crisis.However,it is impeded by the relatively high overpotential and low energy efficiency due to the lack of efficient electrocatalysts.Herein,we develop an isolated single-atom Ni catalyst regulated strategy to activate and stabilize the iron phthalocyanine molecule(Ni SA@FePc)toward a highly efficient CO_(2)RR process at low overpotential.The well-defined and homogenous catalytic centers with unique structures confer Ni SA@FePc with a significantly enhanced CO_(2)RR performance compared to single-atom Ni catalyst and FePc molecule and afford the atomic understanding on active sites and catalytic mechanism.As expected,Ni SA@FePc exhibits a high selectivity of more significant Faraday efficiency(≥95%)over a wide potential range,a high current density of~252 mA·cm^(−2) at low overpotential(390 mV),and excellent long-term stability for CO_(2)RR to CO.X-ray absorption spectroscopy measurement and theoretical calculation indicate the formation of NiN_(4)-O_(2)-FePc heterogeneous structure for Ni SA@FePc.And CO_(2)RR prefers to occur at the raised N centers of NiN4-O_(2)-FePc heterogeneous structure for Ni SA@FePc,which enables facilitated adsorption of*COOH and desorption of CO,and thus accelerated overall reaction kinetics.

pH Overpotential for Unveiling the pH Gradient Effect of H^(+)/OH^(−)Transport in Electrode Reaction Kinetics

The pH gradient caused by H^(+)/OH^(−)transport on an electrode surface is the key factor determining reaction performance,but its detailed impact on the electrode reaction kinetics has yet to be clarified.Here,the pH gradient effect was determined by developing electrode reaction equations,considering the overpotential assigned to the pH gradient called pH overpotential.The pH gradient effect was revealed to involve two aspects:(1)the Nernst pH overpotential,accounting for the common Nernst relationship with pH,and(2)the pH-dependent function of the electron-transfer coefficient(α_(pH)).Both parts were verified experimentally using oxygen reduction reaction and hydrogen evolution reaction,obviously,with differentα_(pH) functions.Detailedα_(pH) function effect was clarified based on numerical calculations of the electrode reaction equations.We found that the effect could be assessed suitably by an apparent constant(α_(app))and a nonlinear fitting method proposed forα_(app) value estimation.The results of this study provide the kinetic fundamentals of electrode reactions involving H^(+)/OH^(−)and contribute to the understanding and assessment of their performance with the H^(+)/OH^(−)transport effect.

Effective ethanol-to-CO_(2) electrocatalysis at iridium-bismuth oxide featuring the impressive negative shifting of the working potential

Since low overpotential for the anodic ethanol oxidation reaction(EOR)can favor the higher output voltage and power of direct ethanol fuel cells(DEFCs),it is critical to design new EOR catalysts with efficient ethanol-to-CO_(2)activity at low applied potentials.Thereby,carbon-supported Ir-Bi_(2)O_(3)(Ir-Bi_(2)O_(3)/C)catalysts with highly dispersive bismuth oxide on the iridium surface are designed and prepared,which can merit splitting the ethanol C–C bond and promoting the oxidation of C1 intermediates at the bifunctional interfaces.The as-obtained Ir-Bi2O3/C catalysts show superior EOR mass activity of up to ca.2250 m A mgIr-1.Moreover,they exhibit the record lowest onset oxidation potentials(0.17–0.22 V vs.RHE)and the peak potential(ca.0.58 V vs.RHE),being 130–300 m V lower than the previous landmark noble metallic catalysts.Furthermore,an apparent C1 pathway faraday efficiency(FEC1)of 28%±5.9%at 0.5 V vs.RHE can be obtained at Ir-Bi_(2)O_(3)/C.This work might provide new insights into the new anodic EOR catalysts for increasing the power of DEFCs.

Microstructure and depositional mechanism of Ni-P coatings with nano-ceria particles by pulse electrodeposition

Nano-CeO2 （RE） particles were co-deposited into Ni-P binary composite coatings by applying pulse current （PC） under ultrasonic （U） field. Morphology, chemical content and crystal microstructure were characterized by environmental scanning electron microscopy （E-SEM） with energy dispersive X-ray analysis （EDXA）, XRD diffractometry and transmission electron microscopy （TEM）. Experimental results show that Ni-P coating reinforced with 15g/L nano-CeO2, in amorphous state and with compact structure, can be improved in the microhardness from HV0.2580 to HV0.2780 by annealing at 600 °C for 2 h. The highest content of codeposited Ce and deposition rate can reach 2.3% and 68 μm/h, respectively. Furthermore, the effect of RE adsorption and pulse overpotential on depositional mechanism was investigated. n-CeO2 particles or Ce4＋ ions with strong adsorption capacity acted as the catalytic nucleus to improve densification effectively. During annealing at 600 °C for 2 h, n-CeO2 particles will uniformly adsorb on crystal grain to preferentially pad and heal up gaps of cracking Ni boundaries, promoting dispersion strengthening with refiner-grained structure.

金属电积中节能阳极的研究

本文研究了钛基IrO_2-PAN电极的制备,得到了一种有实际意义的新型节能阳极(锌电积条件下,η02=0.316V,在i=20,000A/m^2的加速寿命实验中τ=118.4hr)。该电极寿命较长,价格不算高,有工业生产可行性,可节约消耗在电解池部分的能量25%。还考察了不同制备条件对电极表面结构及电化学性能的影响,得出了最佳电极的大致表面结构。

Kinetics Study on O2 Adsorption and OHad Desorption at Pt（111）, Its Implication to Oxygen Reduction Reaction Kinetics

Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.

In situ growth of minimal Ir-incorporated CoxNi1-xO nanowire arrays on Ni foam with improved electrocatalytic activity for overall water splitting

Exploration of cost-effective electrocatalysts for boosting the overall water-splitting efficiency is vitally important for obtaining renewable fuels such as hydrogen.Here,earth-abundant CoxNi1-xO nanowire arrays were used as a structural framework to dilute Ir incorporation for fabricating electrocatalysts for water splitting.Minimal Ir-incorporated CoxNi1-xO nanowire arrays were synthesized through the facile hydrothermal method with subsequent calcination by using Ni foam(NF)as both the substrate and source of Ni.The electrocatalytic water-splitting performance was found to crucially depend on the Ir content of the parent CoxNi1-xO nanowire arrays.As a result,for a minimal Ir content,as low as 0.57 wt%,the obtained Ir-CoxNi1-xO/NF electrodes exhibited optimal catalytic activity in terms of a low overpotential of 260 mV for the oxygen evolution reaction and 53 mV for the hydrogen evolution reaction at 10 mA cm?2 in 1 mol L–1 KOH.When used as bifunctional electrodes in water splitting,the current density of 10 mA cm–2 was obtained at a low cell voltage of 1.55 V.Density functional theory calculations revealed that the Ir-doped CoxNi1-xO arrays exhibited enhanced electrical conductivity and low Gibbs free energy,which contributed to the improved electrocatalytic activity.The present study presents a new strategy for the development of transition metal oxide electrocatalysts with low levels of Ir incorporation for efficient water splitting.

N-heterocyclic carbene as a promising metal-free electrocatalyst with high efficiency for nitrogen reduction to ammonia

Electrocatalytic nitrogen reduction reaction(NRR)at ambient conditions holds great promise for sustainably synthesizing ammonia(NH3),while developing highly-efficient,long-term stable,and inexpensive catalysts to activate the inert N≡N bond is a key scientific issue.In this work,on the basis of the concept"N-heterocyclic carbenes(NHCs)",we propose a carbon decorated graphitic-carbon nitride(C/g-C3N4)as novel metal-free NRR electrocatalyst by means of density functional theory(DFT)computations.Our results reveal that the introduced C atom in g-C3N4 surface can be regarded as NHCs and catalytic sites for activating N≡N bond,and are stabilized by the g-C3N4 substrate due to sterically disfavored dimerization.Especially,this NHCs-based heterogeneous catalysis can efficiently reduce the activated N2 molecule to NH3 with a low overpotential of 0.05 V via an enzymatic mechanism.Our work is the first report of NHCs-based electrocatalyst for N2 fixation,thus opening an alternative avenue for advancing sustainable NH3 production.

A systematical study on the electrodeposition process of metallic lithium

In this study,commercial copper(Cu)foil and Cu foam are used as the working electrodes to systematically investigate the electrochemical deposition and dissolution processes of metallic lithium(Li)on these electrodes;Li metal deposited on the Cu foil electrode is porous and loose.The surface solid electrolyte interface(SEI)film after dissolution from Li dendrites maintains a dendritic porous structure,resulting in a large volume effect of the electrode during the cycle.The Cu foam electrode provides preferential nucleation and deposition sites near the side surface of the separator;the difference in Li affinity results in a heterogeneous deposition and dendrite growth of metallic Li.

Environment friendly hydrothermal synthesis of carbon–Co3O4 nanorods composite as an efficient catalyst for oxygen evolution reaction

The design of cost-effective, highly active catalysts for hydrogen energy production is a vital element in the societal pursuit of sustainable energy. Water electrolysis is one of the most convenient processes to produce high purity hydrogen. Cobalt-based catalysts are well-known electrocatalysts for oxygen evolution reaction（OER）. In this article, all these merits indicate that the present cobalt nanocomposite is a promising electrocatalyst for OER. C–CoO-nanorods catalyst with nanorod structure was synthesized by hydrothermal treatment of CoCl·6HO/dextrose/urea mixture at 180 °C for 18 h and then calcined at400 °C for 3.5 h. The role of dextrose percentage in solution to achieve the uniform coating of carbon on the surface of CoO-nanorods has been demonstrated. The prepared materials were characterized by X-ray diffraction（XRD）, X-ray photoelectron spectrum（XPS）, field emission scanning electron microscopy（FE-SEM）, high-resolution transmission electron microscopy（HR-TEM）, and Brunauer–Emmett–Teller instrument（BET）. Due to its unique morphology, the C–CoO-nanorods catalyst exhibited better activity than CoO-microplates catalyst for OER in 1 M KOH aqueous solution. The results showed a highly efficient, scalable, and low-cost method for developing highly active and stable OER electrocatalysts in alkaline solution.

A theoretical study of electrocatalytic ammonia synthesis on single metal atom/MXene

Electrocatalytic ammonia synthesis under mild conditions is an attractive and challenging process in the earth’s nitrogen cycle,which requires efficient and stable catalysts to reduce the overpotential.The N2 activation and reduction overpotential of different Ti3C2O2-supported transition metal(TM)(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Mo,Ru,Rh,Pd,Ag,Cd,and Au)single-atom catalysts have been analyzed in terms of the Gibbs free energies calculated using the density functional theory(DFT).The end-on N2 adsorption was more energetically favorable,and the negative free energies represented good N2 activation performance,especially in the presence Fe/Ti3C2O2(﹣0.75 eV).The overpotentials of Fe/Ti3C2O2,Co/Ti3C2O2,Ru/Ti3C2O2,and Rh/Ti3C2O2 were 0.92,0.89,1.16,and 0.84 eV,respectively.The potential required for ammonia synthesis was different for different TMs and ranged from 0.68 to 2.33 eV.Two possible potential-limiting steps may be involved in the process:(i)hydrogenation of N2 to*NNH and(ii)hydrogenation of*NH2 to ammonia.These catalysts can change the reaction pathway and avoid the traditional N–N bond-breaking barrier.It also simplifies the understanding of the relationship between the Gibbs free energy and overpotential,which is a significant factor in the rational designing and large-scale screening of catalysts for the electrocatalytic ammonia synthesis.

Electrochemical properties of powder-pressed Pb-Ag-PbO_(2) anodes

Pb?Ag?PbO2 composite anodes with different mass fractions(1%,2%,3%,4%and 5%)ofβ-PbO2 were prepared by powder-pressed(PP)method.The galvanostatic polarization curves,Tafel curves and anodic polarization curves were tested in sulfuric acid solution.The morphologies and phase compositions of the anodic layers formed after galvanostatic polarization were investigated by using scanning electron microscope(SEM)and X-ray diffractometer(XRD),respectively.The results showed thatβ-PbO2 can improve the electrocatalytic activity of anodic oxide.The anode containing 3%β-PbO2 had the lowest overpotential of oxygen evolution reaction(OER)and the best corrosion resistance.The morphologies of the anode surfaces were gradually transformed from regular crystals to amorphous ones as the content ofβ-PbO2 increased in anodes.

Mathematical analysis of SOFC based on co-ionic conducting electrolyte

In co-ionic conducting solid oxide fuel cell （SOFC）, both oxygen ion （O2） and proton （H＋） can transport through the electrolyte, generating steam in both the an-ode and cathode. Thus the mass transport phenomenon in the electrodes is quite different from that in conventional SOFC with oxygen ion conducting electrolyte （O-SOFC） or with proton conducting electrolyte （H-SOFC）. The generation of steam in both electrodes also affects the concentration over-potential loss and further the SOFC performance. However, no detailed modeling study on SOFCs with co-ionic electrolyte has been reported yet. In this paper, a new mathematical model for SOFC based on co-ionic electrolyte was developed to predict its actual performance considering three major kinds of overpotentials. Ohm＇s law and the Butler-Volmer formula were used to model the ion conduction and electrochemical reactions, respectively. The dusty gas model （DGM） was employed to simulate the mass transport processes in the porous electrodes. Parametric simulations were performed to investigate the effects of proton transfer number （tH） and current density （jtotal） on the cell performance. It is interesting to find that the co-ionic conducting SOFC could perform better than O-SOFC and H-SOFC by choosing an appropriate proton transfer number. In addition, the co-ionic SOFC shows smaller difference between the anode and cathode concentration overpotentials than O-SOFC and H-SOFC at certain t H values. The results could help material selection for enhancing SOFC performance.