The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was s...The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.展开更多
A new method of oscillographic chronopotentiometry at silver disk electrode was investigated. By using it, a series of ions such as Pb, In, Cr, Tl, Bi etc. were determined. The detection limits are two or three orders...A new method of oscillographic chronopotentiometry at silver disk electrode was investigated. By using it, a series of ions such as Pb, In, Cr, Tl, Bi etc. were determined. The detection limits are two or three orders of magnitude lower than those by oscillographic chronopotentiometry at mercury electrode. The proposed method is characterized by fine sensitivity, stable oscillogram and no mercury. The research on the mechanism of this method shows that these achievements are caused by the characterristics of silver electroxidation and electroreduction and the oscillographic chronopotentiometry (OC).展开更多
The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffu...The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate o constant koapp, equal to the true rate constant ko describing the redox reaction of interest on the surface of the nanoparticles and the ratio,ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I-1 versus ω-1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof koapp, not ko. Thus, for ψ 〉 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ 〈 1 the deduced electrochemical rate constant will be less than ko. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts.展开更多
The electrolysis of catechol was studied in the pH values of 1 to 10. The results from the rotating ring disk electrode (RRDE) experiments show that at low pH values, the electrochemical polymerization of catechol wa...The electrolysis of catechol was studied in the pH values of 1 to 10. The results from the rotating ring disk electrode (RRDE) experiments show that at low pH values, the electrochemical polymerization of catechol was performed by one step, and at higher pH values, the electrochemical polymerization of catechol was carried out by two steps, i.e . oxidation of catechol and followed by polymerization. The intermediates generated at the disk were detected at the ring electrode in the ring potential region of -0.2 to 0 V (vs. Ag/AgCl). One of reasons for the decrease in the ratio of i r to i d with increasing the ring potential is caused by formation of positively charged intermediates at the disk electrode. This ratio increases with increasing the rotation rate of the RRDE, which indicates that the intermediates are not stable. A shielding effect during polymerization of catechol was observed when the ring potential was set at 0.1 V (vs. Ag/AgCl). The electron spin resonance (ESR) of polycatechol shows that polycatechol possesses unpaired electrons. The images of polycatechol films synthesized at different conditions are described.展开更多
In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance.This aspect...In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance.This aspect can be investigated by employing a model that depicts the local environment for the reduction reactions. Simultaneously, electrochemical impedance spectroscopy, despite being a versatile technique, has rarely been adopted for studying the mass transport features during the carbon dioxide(CO_(2))electroreduction. In this work, this aspect is deeply analyzed by correlating the results of impedance spectroscopy characterization with those obtained by a bubble-induced mass transport modeling under controlled diffusion conditions on a gold rotating disk electrode. The effects of potential and rotation rate on the local environment are also clarified. In particular, it has been found that CO_(2) depletion occurs at high kinetics when the rotation is absent, giving rise to an increment of the competing hydrogen evolution reaction. This feature reflects in an enlargement of the diffusion resistance, which overcomes the charge transport one.展开更多
Magnesium ions, which exist in formation water and injection water under downhole conditions in the oil and gas production industry, are a key determinant in the CaCO_3 scale formation. Many studies have focused their...Magnesium ions, which exist in formation water and injection water under downhole conditions in the oil and gas production industry, are a key determinant in the CaCO_3 scale formation. Many studies have focused their attention on the effect of magnesium on the kinetics, the morphology and the content of Mg in the CaCO_3 scale. Little attention has been paid to the effect of Mg 2+ on the initial stages of CaCO_3 formation on a metal surface. In this study, an electrochemical technique was used to study the influence of Mg 2+ on the initial stages of CaCO_3 scale formed on a metal surface. With this electrochemical technique, the reduction of the dissolved oxygen in an analysis solution is considered on the surface of a rotating disk electrode(RDE) under potentiostatic control.The rate of oxygen reduction on the surface of the RDE enables the extent of surface coverage of scale to be assessed. With this electrochemical technique, a new insight into the effect of Mg 2+ on CaCO_3 scale formed on a metal surface is given.展开更多
Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effectiv...Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8(ZIF-8)and carbon nanotube(CNT)composite catalysts(ZIF-8@CNT)prepared via high-temperature pyrolysis at 900℃.The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells(AEMFC).The prepared metal-free(ZNT-900),single-metal-doped(Fe-ZNT-900,Co-ZNT-900)and binary-metal-doped(Fe_(1)Co_(1)-ZNT-900,Fe_(1)Co_(2)-ZNT-900)catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials.N_(2) adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900,while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts.Binary-metal-doped catalysts showed the highest number of ORR-active sites(pyridinic-N,pyrrolic-N,graphitic-N,M–Nx)and exhibited a half-wave potential(E_(1/2))of 0.846 and 0.847 V vs.RHE for Fe_(1)Co_(1)-ZNT-900 and Fe_(1)Co_(2)-ZNT-900,respectively,which surpassed that of the commercial Pt/C catalyst(E_(1/2)=0.834 V).In H_(2)–O_(2) AEMFCs,the Fe_(1)Co_(2)-ZNT-900 catalyst delivered a maximum power density(P_(max))of 0.171 W cm^(-2) and current density at 0.5 V(j_(0.5))of 0.326 A cm^(-2),which is very close to that of the Pt/C catalyst(P_(max)=0.215 W cm^(-2) and j_(0.5)=0.359 A cm^(-2)).The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.展开更多
The cyclic voltammetry (CV) and the semidifferential anodic stripping voltammetry (SdASV) were used for investigation of bismuth(III) underpotential deposition (UPD) on gold electrode. Based on the excellent electro...The cyclic voltammetry (CV) and the semidifferential anodic stripping voltammetry (SdASV) were used for investigation of bismuth(III) underpotential deposition (UPD) on gold electrode. Based on the excellent electrochemical properties of Au/Bi UPD system, a new method for determining bismuth(III) was established. A solution of 0.1 mol/L HNO 3 was selected as the supporting electrolyte. Factors affecting the Bi(III) UPD and stripping steps were investigated and an optimized analytical procedure was developed. The calibration plots for Bi(III) concentration in the range 1.25×10 -8 -1.0×10 -7 mol/L were obtained. The detection limit, calculated as three times the standard deviation of the analytical signal of 8.3×10 -8 mol/L for a 90 s electrodeposition at 0.00 V (while the solution magnetically stirred at a speed of 300 rpm), was 7.5×10 -9 mol/ L. For 8 successive determinations of 1.25×10 -7 mol/L Bi(III), the obtained RSD (relative standard deviation) was 0.4%. The developed method was applied to bismuth determining in medicine and urine samples. The analytical results were compared with that of atomic emission spectrometry (AES) method.展开更多
Fabrication of superior catalytic performance palladium-based catalysts with affordable cost is the key to develop direct ethanol fuel cell.Herein,Pd-decorated three-dimensional(3D)porous constructed from graphene oxi...Fabrication of superior catalytic performance palladium-based catalysts with affordable cost is the key to develop direct ethanol fuel cell.Herein,Pd-decorated three-dimensional(3D)porous constructed from graphene oxide(GO)and MXene combining with polystyrene(PS)particles as sacrificial templates(Pd/GO-MXene-PS)to elevate the catalytic performance for ethanol oxidation was proposed.The 3D porous interconnected structure of Pd/GO-MXene-PS was characterized by scanning electron microscope(SEM),transmission electron microscope(TEM)and Brunner−Emmet−Teller(BET).By optimizing the doping ratio of MXene to GO,the mass activity of Pd/GO_(5)-MXene_(5)-PS(2944.0 mA·mg^(−1))was 3.0 times higher than that of commercial Pd/C(950.4 mA·mg^(−1))toward ethanol oxidation in base solution.Meanwhile,the rotating disk electrode(RDE)results demonstrated that Pd/GO5-MXene5-PS had a faster kinetics of ethanol oxidation.The enhanced ethanol oxidation over Pd/GO5-MXene5-PS could attribute to the excellent 3D interconnected porous structure,large surface area,good conductivity and homogeneous Pd distribution.This work provided a new idea for creating 3D porous MXene composite materials in electrocatalysis.展开更多
文摘The cyclic voltammetry(CV) and the square wave technique were used for the investigations of thallium(Ⅰ) underpotential deposition(UPD) on the silver electrode. A solution of 10 \{mmol/L\} HClO 4+10 mmol/L NaCl was selected as the supporting electrolyte. The calibration plots for Tl(Ⅰ) concentration in the range of 2×10 -9 -1×10 -7 mol/L were obtained. The detection limit was 5×10 -10 mol/L. For the solutions of 4 0×10 -9 mol/L thallium added before the urine sample pretreatment procedure, the average recovery was 105 6% with a relative standard deviation(RSD) of 15 5%.
文摘A new method of oscillographic chronopotentiometry at silver disk electrode was investigated. By using it, a series of ions such as Pb, In, Cr, Tl, Bi etc. were determined. The detection limits are two or three orders of magnitude lower than those by oscillographic chronopotentiometry at mercury electrode. The proposed method is characterized by fine sensitivity, stable oscillogram and no mercury. The research on the mechanism of this method shows that these achievements are caused by the characterristics of silver electroxidation and electroreduction and the oscillographic chronopotentiometry (OC).
文摘The application of naive Koutecky-Levich analysis to micro- and nano-particle modified rotating disk electrodes of partially covered and non-planar geometry is critically analysed. Assuming strong overlap of the diffusion fields of the particles such that transport to the entire surface is time-independent and one-dimensional, the observed voltammetric response reflects an apparent electrochemical rate o constant koapp, equal to the true rate constant ko describing the redox reaction of interest on the surface of the nanoparticles and the ratio,ψ, of the total electroactive surface area to the geometric area of the rotating disk surface. It is demonstrated that Koutecky-Levich analysis is applicable and yields the expected plots of I-1 versus ω-1 where I is the current and ω is the rotation speed but that the values of the electrochemical rate constants inferred are thereof koapp, not ko. Thus, for ψ 〉 1 apparent electrocatalysis might be naively but wrongly inferred whereas for ψ 〈 1 the deduced electrochemical rate constant will be less than ko. Moreover, the effect of ψ on the observed rotating disk electrode voltammograms is significant, signalling the need for care in the overly simplistic application of Koutecky-Levich analysis to modified rotating electrodes, as is commonly applied for example in the analysis of possible oxygen reduction catalysts.
基金ProjectsupportedbytheNationalNaturalScienceFoundationofChina (No .2 0 0 740 2 7)
文摘The electrolysis of catechol was studied in the pH values of 1 to 10. The results from the rotating ring disk electrode (RRDE) experiments show that at low pH values, the electrochemical polymerization of catechol was performed by one step, and at higher pH values, the electrochemical polymerization of catechol was carried out by two steps, i.e . oxidation of catechol and followed by polymerization. The intermediates generated at the disk were detected at the ring electrode in the ring potential region of -0.2 to 0 V (vs. Ag/AgCl). One of reasons for the decrease in the ratio of i r to i d with increasing the ring potential is caused by formation of positively charged intermediates at the disk electrode. This ratio increases with increasing the rotation rate of the RRDE, which indicates that the intermediates are not stable. A shielding effect during polymerization of catechol was observed when the ring potential was set at 0.1 V (vs. Ag/AgCl). The electron spin resonance (ESR) of polycatechol shows that polycatechol possesses unpaired electrons. The images of polycatechol films synthesized at different conditions are described.
文摘In the electrochemical conversion of carbon dioxide, high currents need to be employed to obtain large production rates, thus implying that mass transport of reactants and products is of crucial importance.This aspect can be investigated by employing a model that depicts the local environment for the reduction reactions. Simultaneously, electrochemical impedance spectroscopy, despite being a versatile technique, has rarely been adopted for studying the mass transport features during the carbon dioxide(CO_(2))electroreduction. In this work, this aspect is deeply analyzed by correlating the results of impedance spectroscopy characterization with those obtained by a bubble-induced mass transport modeling under controlled diffusion conditions on a gold rotating disk electrode. The effects of potential and rotation rate on the local environment are also clarified. In particular, it has been found that CO_(2) depletion occurs at high kinetics when the rotation is absent, giving rise to an increment of the competing hydrogen evolution reaction. This feature reflects in an enlargement of the diffusion resistance, which overcomes the charge transport one.
文摘Magnesium ions, which exist in formation water and injection water under downhole conditions in the oil and gas production industry, are a key determinant in the CaCO_3 scale formation. Many studies have focused their attention on the effect of magnesium on the kinetics, the morphology and the content of Mg in the CaCO_3 scale. Little attention has been paid to the effect of Mg 2+ on the initial stages of CaCO_3 formation on a metal surface. In this study, an electrochemical technique was used to study the influence of Mg 2+ on the initial stages of CaCO_3 scale formed on a metal surface. With this electrochemical technique, the reduction of the dissolved oxygen in an analysis solution is considered on the surface of a rotating disk electrode(RDE) under potentiostatic control.The rate of oxygen reduction on the surface of the RDE enables the extent of surface coverage of scale to be assessed. With this electrochemical technique, a new insight into the effect of Mg 2+ on CaCO_3 scale formed on a metal surface is given.
基金The present work was financially supported by the Estonian Research Council(grants PRG723,PRG4 and PRG1509).
文摘Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction(ORR)in alkaline media is important for fuel cell applications.Herein,we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8(ZIF-8)and carbon nanotube(CNT)composite catalysts(ZIF-8@CNT)prepared via high-temperature pyrolysis at 900℃.The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells(AEMFC).The prepared metal-free(ZNT-900),single-metal-doped(Fe-ZNT-900,Co-ZNT-900)and binary-metal-doped(Fe_(1)Co_(1)-ZNT-900,Fe_(1)Co_(2)-ZNT-900)catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials.N_(2) adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900,while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts.Binary-metal-doped catalysts showed the highest number of ORR-active sites(pyridinic-N,pyrrolic-N,graphitic-N,M–Nx)and exhibited a half-wave potential(E_(1/2))of 0.846 and 0.847 V vs.RHE for Fe_(1)Co_(1)-ZNT-900 and Fe_(1)Co_(2)-ZNT-900,respectively,which surpassed that of the commercial Pt/C catalyst(E_(1/2)=0.834 V).In H_(2)–O_(2) AEMFCs,the Fe_(1)Co_(2)-ZNT-900 catalyst delivered a maximum power density(P_(max))of 0.171 W cm^(-2) and current density at 0.5 V(j_(0.5))of 0.326 A cm^(-2),which is very close to that of the Pt/C catalyst(P_(max)=0.215 W cm^(-2) and j_(0.5)=0.359 A cm^(-2)).The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst.
文摘The cyclic voltammetry (CV) and the semidifferential anodic stripping voltammetry (SdASV) were used for investigation of bismuth(III) underpotential deposition (UPD) on gold electrode. Based on the excellent electrochemical properties of Au/Bi UPD system, a new method for determining bismuth(III) was established. A solution of 0.1 mol/L HNO 3 was selected as the supporting electrolyte. Factors affecting the Bi(III) UPD and stripping steps were investigated and an optimized analytical procedure was developed. The calibration plots for Bi(III) concentration in the range 1.25×10 -8 -1.0×10 -7 mol/L were obtained. The detection limit, calculated as three times the standard deviation of the analytical signal of 8.3×10 -8 mol/L for a 90 s electrodeposition at 0.00 V (while the solution magnetically stirred at a speed of 300 rpm), was 7.5×10 -9 mol/ L. For 8 successive determinations of 1.25×10 -7 mol/L Bi(III), the obtained RSD (relative standard deviation) was 0.4%. The developed method was applied to bismuth determining in medicine and urine samples. The analytical results were compared with that of atomic emission spectrometry (AES) method.
基金financially supported by the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(No.A30B191410)the Sailing Project from Science and Technology Commission of Shanghai Municipality(No.17YF1406600)+6 种基金Chenguang Project Supported by Shanghai Municipal Education Commission(No.18CG68)Gaoyuan Discipline of Shanghai-Materials Science and Engineering(No.A30NH221903)the Open Project of Jiangsu Key Laboratory for Carbon-Based Functional Materials&Devices(Soochow University)(No.KS2022)Collaborative Innovation Center of Suzhou Nano Science&Technologythe 111 ProjectJoint International Research Laboratory of Carbon-Based Functional Materials and Devicesthe Project of Guangdong Provincial Education(No.2020KTSCX131)。
文摘Fabrication of superior catalytic performance palladium-based catalysts with affordable cost is the key to develop direct ethanol fuel cell.Herein,Pd-decorated three-dimensional(3D)porous constructed from graphene oxide(GO)and MXene combining with polystyrene(PS)particles as sacrificial templates(Pd/GO-MXene-PS)to elevate the catalytic performance for ethanol oxidation was proposed.The 3D porous interconnected structure of Pd/GO-MXene-PS was characterized by scanning electron microscope(SEM),transmission electron microscope(TEM)and Brunner−Emmet−Teller(BET).By optimizing the doping ratio of MXene to GO,the mass activity of Pd/GO_(5)-MXene_(5)-PS(2944.0 mA·mg^(−1))was 3.0 times higher than that of commercial Pd/C(950.4 mA·mg^(−1))toward ethanol oxidation in base solution.Meanwhile,the rotating disk electrode(RDE)results demonstrated that Pd/GO5-MXene5-PS had a faster kinetics of ethanol oxidation.The enhanced ethanol oxidation over Pd/GO5-MXene5-PS could attribute to the excellent 3D interconnected porous structure,large surface area,good conductivity and homogeneous Pd distribution.This work provided a new idea for creating 3D porous MXene composite materials in electrocatalysis.
