Probing the electric double layer structure at nitrogen-doped graphite electrodes by constant-potential molecular dynamics simulations

Electric double layer(EDL)is a critical topic in electrochemistry and largely determines the working performance of lithium batteries.However,atomic insights into the EDL structures on heteroatom-modified graphite anodes and EDL evolution with electrode potential are very lacking.Herein,a constant-potential molecular dynamics(CPMD)method is proposed to probe the EDL structure under working conditions,taking N-doped graphite electrodes and carbonate electrolytes as an example.An interface model was developed,incorporating the electrode potential and atom electronegativities.As a result,an insightful atomic scenario for the EDL structure under varied electrode potentials has been established,which unveils the important role of doping sites in regulating both the EDL structures and the following electrochemical reactions at the atomic level.Specifically,the negatively charged N atoms repel the anions and adsorb Li~+at high and low potentials,respectively.Such preferential adsorption suggests that Ndoped graphite can promote Li~+desolvation and regulate the location of Li~+deposition.This CPMD method not only unveils the mysterious function of N-doping from the viewpoint of EDL at the atomic level but also applies to probe the interfacial structure on other complicated electrodes.

Potential-dependent insights into the origin of high ammonia yield rate on copper surface via nitrate reduction:A computational and experimental study

Focusing on revealing the origin of high ammonia yield rate on Cu via nitrate reduction(NO3RR),we herein applied constant potential method via grand-canonical density functional theory(GC-DFT)with implicit continuum solvation model to predict the reaction energetics of NO3RR on pure copper surface in alkaline media.The potential-dependent mechanism on the most prevailing Cu(111)and the minor(100)and(110)facets were established,in consideration of NO_(2)_(−),NO,NH_(3),NH_(2)OH,N_(2),and N_(2)O as the main products.The computational results show that the major Cu(111)is the ideal surface to produce ammonia with the highest onset potential at 0.06 V(until−0.37 V)and the highest optimal potential at−0.31 V for ammonia production without kinetic obstacles in activation energies at critical steps.For other minor facets,the secondary Cu(100)shows activity to ammonia from−0.03 to−0.54 V with the ideal potential at−0.50 V,which requires larger overpotential to overcome kinetic activation energy barriers.The least Cu(110)possesses the longest potential range for ammonia yield from−0.27 to−1.12 V due to the higher adsorption coverage of nitrate,but also with higher tendency to generate di-nitrogen species.Experimental evaluations on commercial Cu/C electrocatalyst validated the accuracy of our proposed mechanism.The most influential(111)surface with highest percentage in electrocatalyst determined the trend of ammonia production.In specific,the onset potential of ammonia production at 0.1 V and emergence of yield rate peak at−0.3 V in experiments precisely located in the predicted potentials on Cu(111).Four critical factors for the high ammonia yield and selectivity on Cu surface via NO3RR are summarized,including high NO3RR activity towards ammonia on the dominant Cu(111)facet,more possibilities to produce ammonia along different pathways on each facet,excellent ability for HER inhibition and suitable surface size to suppress di-nitrogen species formation at high nitrate coverage.Overall,our work provides comprehensive potential-dependent insights into the reaction details of NO3RR to ammonia,which can serve as references for the future development of NO3RR electrocatalysts,achieving higher activity and selectivity by maximizing these characteristics of copper-based materials.

THE VERIFICATION OF THE CURRENT TRANSIENT EQUATION AT TUBULAR ELECTRODES IN A FLOWING FLUID UNDER POTENTIAL STEP

The equation derived for the response of the current transients in the flowing fluid is verified experimentally.

Electrode Potential Explaining the Growth of Anodic Oxides

The formation mechanism of porous anodic oxides remains unclear till now.The classical field-assisted dissolution(FAD)theory cannot explain the relationship between the current curve and FAD reaction,and the influence of the electrode potential on anodization is rarely reported.The electrode potential theory,oxygen bubble model and the ionic current and electronic current theories were introduced to explain the growth of porous anodic oxides of three metals(Ti,Zr and Fe).Taking the anodization of Ti in aqueous solution containing 0.5wt% NH_(4)F as an example,the electrode potential was calculated,and the morphology of porous anodic oxides was investigated at low voltages.Results show that the growth of porous anodic oxides is determined by the ratio of the ionic current to the electronic current.During the anodization,metals are classified into two groups:one is easy to form the compact oxide layer,and the other is easy to induce oxygen releasing,thus forming oxygen bubbles.The electrolyte is also classified into two groups correspondingly:compact oxide layer-assisted electrolyte and releasing oxygen-assisted electrolyte.

Revealing the role of electrode potential micro-environments in single Mn atoms for carbon dioxide and oxygen electrolysis

Elucidation the relationship between electrode potentials and heterogeneous electrocatalytic reactions has attracted widespread attention.Herein we construct the well-defined Mn single-atom(MnSA)catalyst with four N-coordination through a simple thermal pyrolysis preparation method to investigate the electrode potential micro-environments effect on carbon dioxide reduction reactions(CO_(2)RR)and oxygen reduction reactions(ORR).MnSA catalysts generate higher CO production Faradaic efficiency of exceeding 90%at-0.9 V for CO_(2)RR and higher H_(2)O_(2)yield from 0.1 to 0.6 V with excellent ORR activity.Density functional theory(DFT)calculations based on constant potential models were performed to study the mechanism of MnSA on CO_(2)RR.The thermodynamic energy barrier of CO_(2)RR is lowest at-0.9 V vs.reversible hydrogen electrode(RHE).Similar DFT calculations on the H_(2)O_(2)yield of ORR showed that the H_(2)O_(2)yield at 0.2 V was higher.This study provides a reasonable explanation for the role of electrode potential micro-environments.

EFFECTS OF STRESS RATIO AND FREQUENCY ON CORROSION FATIGUE CRACK GROWTH MECHANISM IN LOW ALLOY STEELS

Based on theoretical analysis about local strain,strain rate and dissolving rate at crack tip, the corrosion fatigue crack growth rate of steels ZG20SiMn and SM50B-Zc in fresh water and 3.5% NaCl solution were measured experimentally,and the PH and electrode potential within crack were also measured continuously along with crack propagating.It showed that the increase of crack growth rate,caused by both decreasing frequency and raising stress ratio,was mainly accelerated by hydrogen embrittlement.

Effect of added cobalt ion on copper electrowinning from sulfate bath using doped polyaniline and Pb-Ag anodes

Effect of added Co2 +(aq)on copper electrowinning was studied using doped polyaniline(Pani)and Pb-Ag(1%)anodes and a stainless steel cathode.The presence of added Co2+ (aq)in the electrolyte solution was found to decrease the anode potentials.The optimum level of Co2 +(aq)concentration in the electrolyte,with respect to the maximum saving of power consumption was established.Linear sweep voltammetry(LSV)was used to study the influence of added Co2 +(aq)on the anodic processes in a copper sulfate-sulfuric acid electrolyte.The oxygen-evolution potential for Pani anode is depolarised at lower current densities(≤0.01 A/cm2)and attains saturation atρ(Co 2+ )o≈0.789 g/L;whilst the oxygen-evolution potential for Pb-Ag(1%)anode is depolarised at higher current densities(≤0.02 A/cm2)and attains saturation atρ(Co 2+ )o≈1.315 g/L.The preferred orientations of the copper deposits change from(220)to(111)with the addition of 0.394?0.789 g/L Co 2+ but higher concentrations favor(220)orientation again.

Electrochemical Behavior of Nd^(3+) and Ho^(3+) in LiCl-KCl Eutectic Melt

The electrochemical behavior of Nd 3+ and Ho 3+ ions on molybdenum electrode in the LiCl KCl eutectic melts has been studied by cyclic voltammetry and open circuit potentiometry. The results show that the reduction process of Nd 3+ and Ho 3+ ions on molybdenum electrode is one step three electron reversible reaction. The diffusion coefficients of Nd 3+ and Ho 3+ ions are 1 13×10 -6 cm 2·s -1 (450 ℃) and 2 142×10 -5 cm 2·s -1 (450 ℃), respectively. The measured standard electrode potential of Ho 3+ /Ho is 2 987 V(vs.Cl/Cl -), being more negative than the theoretical one, the reason of which is also discussed.

Stochastic Thermodynamics of Mesoscopic Electrochemical Reactions

In this work, we discussed the stochastic thermodynamics of mesoscopic electron transfer reactions between ions and electrodes. With a relationship between the reaction rate con- stant and the electrode potential, we find that the heat dissipation βq equals to the dynamic irreversibility of the reaction system minus an internal entropy change term. The total en- tropy change Ast is defined as the summation of the system entropy change As and the heat dissipation/βq such that △st=△s＋βq. Even though the heat dissipation depends linearly on the electrode potential, the total entropy change is found to satisfy the fluctuation theo- rem 〈e-△st 〉=1, and hence a second law-like inequality reads （△st）≥0. Our study provides a practical methodology for the stochastic thermodynamics of electrochemical reactions, which may find applications in biochemical and electrochemical reaction systems.

The Combined Impact of Magnetic Field and Chloride Ion Concentration on Corrosion Behavior of Al-Mg Alloys

The impact of magnetic field on the corrosion behavior of Al-Mg-xR_(E)/Fe alloys in NaCl solutions with concentrations of 1.5wt%,3.5wt%,and 5.5wt%were studied by microstructure observation,immersion test,and electrochemical test.The combined impacts of magnetic field and chloride ion concentration on the corrosion behavior of Al-Mg alloys with various electrode potential phases were discussed.The results indicate that Al-3.0Mg-xR_(E)/Fe alloys corrode faster and have a higher pitting corrosion potential in the NaCl solution with a higher concentration.In addition,a magnetic field can lower the pitting sensitivity and corrosion rate of Al-3.0Mg and Al-3.0Mg-0.2R_(E)/Fe alloys in NaCl solution with different concentrations.However,at a higher concentration of NaCl solution,the magnetic field has a weaker inhibiting effect on corrosion rate and pitting sensitivity.In NaCl solutions with concentrations of 1.5wt%and 3.5wt%,the corrosion rate and pitting sensitivity of Al-3.0Mg-1.0R_(E)/Fe alloys can be reduced by a magnetic field.However,in NaCl solution with the concentration of 5.5wt%,the corrosion rate of the alloys is increased by a magnetic field.

Standard potential of the Ag-AgCl electrode and acidity constant of glycine at constant molality of NaCl in glucose-water mixed solvents from 278.15 to 318.15 K

Standard electrode potentials E° of Ag-AgC1 electrode in molality scale and acidity constants of glyeine pK_1° at constant molality of NaCl (1.0 mol·kg^(-1)) in 5 and 15 mass% glucose-water mixed solvents over a range of temperatures from 278.15 to 318.15 K were determined from precise emf measurements.The dependence of acidity constant on temperature is given as a function of the thermodynamic temperature T by an empirical equation, pK_1° =A_1(K/T)-A_2+A_3(T/K).The corresponding thermodynamic quantities of the first dissociation process of glycine were calculated and the effects of both tho solvent and the salt on them were also discussed.

A novel Ce(Ⅳ)ion-selective polyvinyl chloride membrane electrode based on HDEHP and HEH/EHP

A novel Ce（Ⅳ） ion-selective polyvinyl chloride（PVC） membrane electrode based on HDEHP and HEH/EHP as ionophore was successfully prepared. The factors affecting the response of Ce（Ⅳ） ion were investigated, such as membrane composition, internal solution, concentration of SO_4^（2–）, and acidity in test solution. The best performance was obtained using the membrane with PVC：DBP：HDEHP：HEH/EHP：OA mass ratio of 75：175：5：5：5. The proposed electrode exhibited a Nernstian slope of 30.44 mV/decade for Ce（Ⅳ） ion over a linear concentration range of 1×10^（–5）–1×10^（–1） mol/L with the detection limit of 9.0×10^（-6） mol/L. The electrode showed stable response within the SO_4^（2–） concentration range of 0.1–1 mol/L and the acidity range of 0.25–1.2 mol/L H＋. The proposed electrode showed high selectivity for Ce（Ⅳ） over a wide variety of interfering ions and a fast response time. It was used as an indicator in the potentiometric titration of Ce（Ⅳ） solution with H_2O_2 solution, and could also be used for the determination of Ce（Ⅳ） in real Ce（Ⅳ）-containing aqueous samples.