Login In
2019 Volume 82 Issue 5
2019, 82(5): 387-398
Abstract:
Under high pressure (1~100 GPa and above), the composition, structure and chemical reaction of matters change significantly, and it is of great significance to understand the chemical reactions under high pressure. In general, molecules solidify under external pressure, unsaturated molecules tend to polymerize to form covalently bonded saturated material with higher density; diffusions of molecules and atoms are significantly restricted, and metastable compounds are often generated; the crystal structure of the reactants, the properties of the functional groups, the temperature and hydrostaticity have significant effects on the reaction. In situ and ex situ crystallography, spectroscopy, chemical characterization, and theoretical calculations are important for the study of the reaction process, and every effort on the synthesis, characterization, theoretical calculation under high pressure is a new step towards the interesting world under extreme condition.
Under high pressure (1~100 GPa and above), the composition, structure and chemical reaction of matters change significantly, and it is of great significance to understand the chemical reactions under high pressure. In general, molecules solidify under external pressure, unsaturated molecules tend to polymerize to form covalently bonded saturated material with higher density; diffusions of molecules and atoms are significantly restricted, and metastable compounds are often generated; the crystal structure of the reactants, the properties of the functional groups, the temperature and hydrostaticity have significant effects on the reaction. In situ and ex situ crystallography, spectroscopy, chemical characterization, and theoretical calculations are important for the study of the reaction process, and every effort on the synthesis, characterization, theoretical calculation under high pressure is a new step towards the interesting world under extreme condition.
2019, 82(5): 399-403
Abstract:
Fullerene, a spherical carbon allotrope, with excellent photoelectric and biological properties has attracted special attention in the field of biomedicine. Cyclodextrin, a cone-shaped cyclic oligosaccharide, with well-solubility, good biocompatibility and specific inclusion property plays an important role in host-guest chemistry. The fullerene/cyclodextrin composite materials, which combine the advantages of fullerene and cyclodextrin, provide excellent performance in DNA cleavage, photodynamic therapy, drug carriers and other biomedicine fields. Based on the construction of fullerene/cyclodextrin systems, the research progress in non-covalent and covalent composite materials of fullerene/cyclodextrin were reviewed and the application of fullerene/cyclodextrin composite materials is prospected. It provides a reference for the construction of new fullerene/cyclodextrin composite materials.
Fullerene, a spherical carbon allotrope, with excellent photoelectric and biological properties has attracted special attention in the field of biomedicine. Cyclodextrin, a cone-shaped cyclic oligosaccharide, with well-solubility, good biocompatibility and specific inclusion property plays an important role in host-guest chemistry. The fullerene/cyclodextrin composite materials, which combine the advantages of fullerene and cyclodextrin, provide excellent performance in DNA cleavage, photodynamic therapy, drug carriers and other biomedicine fields. Based on the construction of fullerene/cyclodextrin systems, the research progress in non-covalent and covalent composite materials of fullerene/cyclodextrin were reviewed and the application of fullerene/cyclodextrin composite materials is prospected. It provides a reference for the construction of new fullerene/cyclodextrin composite materials.
2019, 82(5): 404-414
Abstract:
Progress in Ni-catalyzed Suzuki coupling reaction including the development path and all kinds of Ni-catalyzed Suzuki coupling reaction (C-Halo bond cleavage, C-O bond cleavage, C-C bond cleavage, C-N bond cleavage and C-S bond cleavage) in the past decade have been reviewed. Through nearly ten years of research, various new catalysts, ligands and additives have been developed, resulting in greatly improved reactivity and milder reaction conditions. The mechanism of Ni-catalyzed Suzuki coupling reaction was analyzed. It was found that Ni catalyzed Suzuki coupling reaction can be divided into Ni(0)/Ni(Ⅱ) cycle and Ni(Ⅰ)/Ni(Ⅲ) cycle. It is considered that the research and development of cheap metal nickel catalyst is an important direction to study the Suzuki coupling reaction. In the future, the study of Ni catalytic Suzuki coupling reaction will focus on mechanism investigation, design of new catalysts and ligands, multi-type C-C bond construction (Csp2-Csp3, Csp3-Csp3) and asymmetric Ni-catalyzed Suzuki coupling reaction of multi-type substrates.
Progress in Ni-catalyzed Suzuki coupling reaction including the development path and all kinds of Ni-catalyzed Suzuki coupling reaction (C-Halo bond cleavage, C-O bond cleavage, C-C bond cleavage, C-N bond cleavage and C-S bond cleavage) in the past decade have been reviewed. Through nearly ten years of research, various new catalysts, ligands and additives have been developed, resulting in greatly improved reactivity and milder reaction conditions. The mechanism of Ni-catalyzed Suzuki coupling reaction was analyzed. It was found that Ni catalyzed Suzuki coupling reaction can be divided into Ni(0)/Ni(Ⅱ) cycle and Ni(Ⅰ)/Ni(Ⅲ) cycle. It is considered that the research and development of cheap metal nickel catalyst is an important direction to study the Suzuki coupling reaction. In the future, the study of Ni catalytic Suzuki coupling reaction will focus on mechanism investigation, design of new catalysts and ligands, multi-type C-C bond construction (Csp2-Csp3, Csp3-Csp3) and asymmetric Ni-catalyzed Suzuki coupling reaction of multi-type substrates.
2019, 82(5): 415-423
Abstract:
How to effectively remove the dyes from the waste water has been the popular direction of materials and environmental science. Compared with traditional adsorption and concentration filtration methods, the photocatalytic degradation has attracted more attention due to its unique environmental-friendly, conveniency, safety and without secondary pollution. In numerous catalysts, heteropoly acid (HPA) has great potential in photocatalytic applications due to its special 'cage' structure, tunable electronic properties, non-toxicity, oxygen-rich surface, cheapness and excellent redox properties, etc. In this paper, the research progress of polyoxometalate-based photocatalysts in recent years was introduced, and they can be classified into two major categories:modification and loading method, which were further subdivided into substitution HPAs, altered counterion HPA, organic and inorganic modification method, silicate loading method, titanium dioxide loading method and graphene loading method. The main improvement direction is to resolve their water solubility problem, broaden the light response range, increase their specific surface area and improve the recyclability. The synthesis conditions and catalytic mechanism of different catalyst systems were summarized and analyzed in detail, at the end, the future development trend is forecasted.
How to effectively remove the dyes from the waste water has been the popular direction of materials and environmental science. Compared with traditional adsorption and concentration filtration methods, the photocatalytic degradation has attracted more attention due to its unique environmental-friendly, conveniency, safety and without secondary pollution. In numerous catalysts, heteropoly acid (HPA) has great potential in photocatalytic applications due to its special 'cage' structure, tunable electronic properties, non-toxicity, oxygen-rich surface, cheapness and excellent redox properties, etc. In this paper, the research progress of polyoxometalate-based photocatalysts in recent years was introduced, and they can be classified into two major categories:modification and loading method, which were further subdivided into substitution HPAs, altered counterion HPA, organic and inorganic modification method, silicate loading method, titanium dioxide loading method and graphene loading method. The main improvement direction is to resolve their water solubility problem, broaden the light response range, increase their specific surface area and improve the recyclability. The synthesis conditions and catalytic mechanism of different catalyst systems were summarized and analyzed in detail, at the end, the future development trend is forecasted.
2019, 82(5): 424-430
Abstract:
A novel cathode material xLiF-(Ni1/6Co1/6Mn4/6)3O4 composites are synthesized by the high energy mechanical milling with different time and the as-prepared composites were modified by the graphene to improve electrochemical performance. X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical test and X-ray photoelectron spectroscopy (XPS) are employed to further characterize the properties of the composites. The resultant cathode has the highest discharge capacity of 157.3mAh·g-1 when ball milling 24h. The xLiF-(Ni1/6Co1/6Mn4/6)3O4 composites with 20% graphene exhibit a discharge capacity of 235 mAh·g-1 (1C=250 mAh·g-1) at 0.05 C from 1.5~4.8 V. The rate capability is also promoted as the discharge specific capacity reaching 151 and 114 mAh·g-1 at 1 C and 5 C respectively. Moreover, the variation of the discharge capacity of the composite cathode along with the cut-off voltage are analyzed, which confirms the potential of higher discharge capacity of the cathode at higher voltage.
A novel cathode material xLiF-(Ni1/6Co1/6Mn4/6)3O4 composites are synthesized by the high energy mechanical milling with different time and the as-prepared composites were modified by the graphene to improve electrochemical performance. X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical test and X-ray photoelectron spectroscopy (XPS) are employed to further characterize the properties of the composites. The resultant cathode has the highest discharge capacity of 157.3mAh·g-1 when ball milling 24h. The xLiF-(Ni1/6Co1/6Mn4/6)3O4 composites with 20% graphene exhibit a discharge capacity of 235 mAh·g-1 (1C=250 mAh·g-1) at 0.05 C from 1.5~4.8 V. The rate capability is also promoted as the discharge specific capacity reaching 151 and 114 mAh·g-1 at 1 C and 5 C respectively. Moreover, the variation of the discharge capacity of the composite cathode along with the cut-off voltage are analyzed, which confirms the potential of higher discharge capacity of the cathode at higher voltage.
2019, 82(5): 431-435
Abstract:
Using graphene oxide (GO), which was prepared from cathodic graphite powder of spent lithium-ion batteries by an improved oxidation-reduction method, and aniline monomer as starting materials, the graphene/polyaniline composites were prepared via in situ polymerization by hydroxyl free radicals (·OH) from GO activated H2O2. The structure of the composite was characterized by FT-IR, XRD and SEM. The electrochemical behavior of the composites electrode was evaluated by cyclicvoltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge tests (GCD). The results showed that the capacitance of rGO/PANI-10 was 481F/g at a current density of 100 mA/g, and it retained 77% capacitance after 1000 cycles at a current density of 500mA/g.
Using graphene oxide (GO), which was prepared from cathodic graphite powder of spent lithium-ion batteries by an improved oxidation-reduction method, and aniline monomer as starting materials, the graphene/polyaniline composites were prepared via in situ polymerization by hydroxyl free radicals (·OH) from GO activated H2O2. The structure of the composite was characterized by FT-IR, XRD and SEM. The electrochemical behavior of the composites electrode was evaluated by cyclicvoltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge tests (GCD). The results showed that the capacitance of rGO/PANI-10 was 481F/g at a current density of 100 mA/g, and it retained 77% capacitance after 1000 cycles at a current density of 500mA/g.
2019, 82(5): 436-440
Abstract:
Using bismuth nitrate pentahydrate and potassium chloride as raw materials, BiOCl was synthesized successfully via hydrothermal method, and its structure was characterized by XRD, SEM, and DRS. The influence of precursor pH value on the structure of BiOCl and the degradation of 8-hydroxyquinoline was investigated. The results showed that the exposure of[001] crystal plane, the band gap energy, and the catalytic activity decrease with the increase of precursor pH, which can be attributed to low band-gap energy and high photo-generated carrier recombination efficiency. The effect of degradation system pH on the reactivity of BiOCl catalyst was further investigated. The results showed that degradation system pH affected the adsorption behavior of 8-hydroxyquinoline on the surface of the catalyst, which in turn affected the reactivity of the catalyst.
Using bismuth nitrate pentahydrate and potassium chloride as raw materials, BiOCl was synthesized successfully via hydrothermal method, and its structure was characterized by XRD, SEM, and DRS. The influence of precursor pH value on the structure of BiOCl and the degradation of 8-hydroxyquinoline was investigated. The results showed that the exposure of[001] crystal plane, the band gap energy, and the catalytic activity decrease with the increase of precursor pH, which can be attributed to low band-gap energy and high photo-generated carrier recombination efficiency. The effect of degradation system pH on the reactivity of BiOCl catalyst was further investigated. The results showed that degradation system pH affected the adsorption behavior of 8-hydroxyquinoline on the surface of the catalyst, which in turn affected the reactivity of the catalyst.
2019, 82(5): 441-445
Abstract:
In this paper, CeCl3·7H2O, Eu2O3 and C2H2O4·2H2O were used as raw materials to prepare europium-doped cerium oxalate by oxalate coprecipitation process. The europium-doped cerium oxalate was calcined into europium-doped cerium oxide precursor. This precursor was vulcanized into europium-doped γ-Ce2S3 by CS2 with Ar as the carrier gas. The results showed that using Eu2+ ion doping can lower the synthesis temperature and improve the temperature stability of europium-doped γ-Ce2S3. When the ratio of Eu2+ and Ce3+ was 0.03, the pure phase of γ-Ce2S3 can be obtained by vulcanized at 900℃ for 150 min. The synthesis temperature of γ-Ce2S3 had decreased by 300℃ than that of pure γ-Ce2S3, and the oxidation exothermic peak of europium-doped γ-Ce2S3 increases from 490.6℃ to 553.3℃.
In this paper, CeCl3·7H2O, Eu2O3 and C2H2O4·2H2O were used as raw materials to prepare europium-doped cerium oxalate by oxalate coprecipitation process. The europium-doped cerium oxalate was calcined into europium-doped cerium oxide precursor. This precursor was vulcanized into europium-doped γ-Ce2S3 by CS2 with Ar as the carrier gas. The results showed that using Eu2+ ion doping can lower the synthesis temperature and improve the temperature stability of europium-doped γ-Ce2S3. When the ratio of Eu2+ and Ce3+ was 0.03, the pure phase of γ-Ce2S3 can be obtained by vulcanized at 900℃ for 150 min. The synthesis temperature of γ-Ce2S3 had decreased by 300℃ than that of pure γ-Ce2S3, and the oxidation exothermic peak of europium-doped γ-Ce2S3 increases from 490.6℃ to 553.3℃.
2019, 82(5): 446-451
Abstract:
Phenylpropionic acid compounds are potential bioactive drugs for G protein coupled receptor 40 (GPR40). Based on the comparative molecular force field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA), the 3D-QSAR models of 40 known active GPR40 receptor phenylpropionic acid agonists were established, respectively. This experiment investigated the 3D-QSAR between this type of agonist and their biological activity. The cross-validation coefficients (q2) of the CoMFA model and CoMSIA model are 0.527 and 0.500, and the fitting verification coefficients (r2) are 0.901 and 0.860. The predicted values of two models are basically consistent with the experimental values, and both models have good predictive ability. Furthermore, according to the information provided by models of the stereo field, electrostatic field, hydrophobic field, hydrogen bond donor field and hydrogen bond acceptor site, the drug design ideas for optimizing the structure of the inhibitor are proposed, and provide a theoretical basis for guiding the design of higher activity GPR40 agonists and the prediction of agonistic activity of new GRR40 molecules.
Phenylpropionic acid compounds are potential bioactive drugs for G protein coupled receptor 40 (GPR40). Based on the comparative molecular force field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA), the 3D-QSAR models of 40 known active GPR40 receptor phenylpropionic acid agonists were established, respectively. This experiment investigated the 3D-QSAR between this type of agonist and their biological activity. The cross-validation coefficients (q2) of the CoMFA model and CoMSIA model are 0.527 and 0.500, and the fitting verification coefficients (r2) are 0.901 and 0.860. The predicted values of two models are basically consistent with the experimental values, and both models have good predictive ability. Furthermore, according to the information provided by models of the stereo field, electrostatic field, hydrophobic field, hydrogen bond donor field and hydrogen bond acceptor site, the drug design ideas for optimizing the structure of the inhibitor are proposed, and provide a theoretical basis for guiding the design of higher activity GPR40 agonists and the prediction of agonistic activity of new GRR40 molecules.
2019, 82(5): 452-456
Abstract:
In this paper, the kinetic thermal activity of laccases in three systems was studied, and the kinetic parameters were analyzed accordingly. The results showed that the inactivation of laccase in pure aqueous solution accords with the first-order kinetic inactivation model, and the inactivation equation was lnA=-0.1353t-2.2522. The inactivation of laccase in the toxic organic system (2, 4-dichlorophenol and indole solution) is still in accordance with the first-order inactivation mechanical model. The inactivation rate constant is reduced, but the half-life is increased. In polar solution (ethanol solution), the reaction rate constant of laccase is the smallest, probably because the change of internal force in laccase molecule causes the laccase reaction to be slow. In the non-polar system (isooctane solution), water-hydrophobic system reduces the damage to the enzyme, which is beneficial to the stability of the enzyme and prolongs the half-life of laccase. The laccase inactivation in the polar or non-polar system is consistent with the first-order kinetic inactivation model.
In this paper, the kinetic thermal activity of laccases in three systems was studied, and the kinetic parameters were analyzed accordingly. The results showed that the inactivation of laccase in pure aqueous solution accords with the first-order kinetic inactivation model, and the inactivation equation was lnA=-0.1353t-2.2522. The inactivation of laccase in the toxic organic system (2, 4-dichlorophenol and indole solution) is still in accordance with the first-order inactivation mechanical model. The inactivation rate constant is reduced, but the half-life is increased. In polar solution (ethanol solution), the reaction rate constant of laccase is the smallest, probably because the change of internal force in laccase molecule causes the laccase reaction to be slow. In the non-polar system (isooctane solution), water-hydrophobic system reduces the damage to the enzyme, which is beneficial to the stability of the enzyme and prolongs the half-life of laccase. The laccase inactivation in the polar or non-polar system is consistent with the first-order kinetic inactivation model.
2019, 82(5): 457-462
Abstract:
The chloromethylated polysulfone (CPS) was obtained by introducing chloromethyl group onto the main chain of PS with 1, 4-bischloromethoxyl butane (BCD) as reagent. Subsequently naphthalenesulfonic acid type side chain polysulfone (PS-NS) was prepared via nucleophilic substitution with 2-naphthol-6, 8-disulfonic acid dipotassium as nucleophilic reagent. The corresponding proton exchange membranes (PEMs) were fabricated by solution casting method after characterizing their structures by FT-IR and 1H NMR. Based on the aliphatic sulfoacid type side chain sulfonated polysulfone (PS-ES) and benzene sulfoacid type side chain sulfonated polysulfone (PS-BS) in our previous research, the effects of side chain structure on performance including wateruptaking, swelling ratio and proton conductivity of PEMs were explored. The results showed that the three kind of PEMs keep better size stability at high wateruptaking compared with the main chain type aromatic PEMs because they could form micro-phase separation by locating the hydrophilic sulfonic acid group far away from hydrophobic polysulfone main chain. As the number of rigid benzene rings in the side chain increases, the flexibility of the side chains weakens, resulting in increased dimensional stability of the PEMs and a corresponding decrease in proton conductivity. The proton conductivity of PS-ES was up to 0.072S/cm at 25℃ and 0.141S/cm at 85℃. The swelling ratio of PS-NS PEM was only 21.8% at 25℃ and 51.5% at 85℃. The performance is close to commercialized Nafion115 PEMs.
The chloromethylated polysulfone (CPS) was obtained by introducing chloromethyl group onto the main chain of PS with 1, 4-bischloromethoxyl butane (BCD) as reagent. Subsequently naphthalenesulfonic acid type side chain polysulfone (PS-NS) was prepared via nucleophilic substitution with 2-naphthol-6, 8-disulfonic acid dipotassium as nucleophilic reagent. The corresponding proton exchange membranes (PEMs) were fabricated by solution casting method after characterizing their structures by FT-IR and 1H NMR. Based on the aliphatic sulfoacid type side chain sulfonated polysulfone (PS-ES) and benzene sulfoacid type side chain sulfonated polysulfone (PS-BS) in our previous research, the effects of side chain structure on performance including wateruptaking, swelling ratio and proton conductivity of PEMs were explored. The results showed that the three kind of PEMs keep better size stability at high wateruptaking compared with the main chain type aromatic PEMs because they could form micro-phase separation by locating the hydrophilic sulfonic acid group far away from hydrophobic polysulfone main chain. As the number of rigid benzene rings in the side chain increases, the flexibility of the side chains weakens, resulting in increased dimensional stability of the PEMs and a corresponding decrease in proton conductivity. The proton conductivity of PS-ES was up to 0.072S/cm at 25℃ and 0.141S/cm at 85℃. The swelling ratio of PS-NS PEM was only 21.8% at 25℃ and 51.5% at 85℃. The performance is close to commercialized Nafion115 PEMs.
2019, 82(5): 463-467
Abstract:
By studying and comparing the effects of different treatment processes on shale gas-fracturing produced water, the process of electrocoagulation-O3 combined treatment of produced water was designed. Taking COD and TSS as indictor, the effects of pH, current density, electrode spacing, electrolysis time and O3 aeration on the removal efficiency of COD and TSS are discussed. The experimental results showed that the most suitable conditions are as follows:pH is 8.0, the current density is 1250 A/m2, the distance between plates is 2 cm, the electrolysis time is 6 min and the O3 ventilation is 40 L/h. Under these conditions, the COD and TSS removal rate of produced-water is 98.3% and 95.9% respectively. The color, turbidity, oil, and NH4-N pollution of the produced water reach the national emission standards after combined treatment with Electrocoagulation-O3.
By studying and comparing the effects of different treatment processes on shale gas-fracturing produced water, the process of electrocoagulation-O3 combined treatment of produced water was designed. Taking COD and TSS as indictor, the effects of pH, current density, electrode spacing, electrolysis time and O3 aeration on the removal efficiency of COD and TSS are discussed. The experimental results showed that the most suitable conditions are as follows:pH is 8.0, the current density is 1250 A/m2, the distance between plates is 2 cm, the electrolysis time is 6 min and the O3 ventilation is 40 L/h. Under these conditions, the COD and TSS removal rate of produced-water is 98.3% and 95.9% respectively. The color, turbidity, oil, and NH4-N pollution of the produced water reach the national emission standards after combined treatment with Electrocoagulation-O3.
2019, 82(5): 468-471
Abstract:
The target compound with nitrogen atom introduced into coronene was synthesized by cyclic reaction with fluorosulfonic acid as catalyst, and its structure was characterized. The properties of the compound were tested, which showed that the compound could be used as a light-emitting device molecule to prepare the electroluminescent materials.
The target compound with nitrogen atom introduced into coronene was synthesized by cyclic reaction with fluorosulfonic acid as catalyst, and its structure was characterized. The properties of the compound were tested, which showed that the compound could be used as a light-emitting device molecule to prepare the electroluminescent materials.
2019, 82(5): 472-475
Abstract:
5-Phenyl-5H-benzo[2, 3]phosphindolo[4, 5-b]benzofuran 4 and 5 were synthesized by dibenzofuran-4-boronic acid as starting material. After Suzuki coupling reaction, lithiation by n-butyllithium and Pd(OAc)2 catalyzed cyclization, the titled compounds were obtained, and their structure were characterized by NMR and HRMS. Their physical-chemical properties were studied using UV, fluorescence spectra and TGA. The results showed that this kind of compounds have potential application in the field of organic electroluminescent materials.
5-Phenyl-5H-benzo[2, 3]phosphindolo[4, 5-b]benzofuran 4 and 5 were synthesized by dibenzofuran-4-boronic acid as starting material. After Suzuki coupling reaction, lithiation by n-butyllithium and Pd(OAc)2 catalyzed cyclization, the titled compounds were obtained, and their structure were characterized by NMR and HRMS. Their physical-chemical properties were studied using UV, fluorescence spectra and TGA. The results showed that this kind of compounds have potential application in the field of organic electroluminescent materials.
2019, 82(5): 476-479
Abstract:
A novel methionine derivative pickling corrosion inhibitor was synthesized. Its structure was identified by IR and NMR. The corrosion inhibition performance of methionine derivative were studied by weight loss and electrochemical methods for A3 steel in 0.5mol·L-1 sulfuric acid medium, and the inhibition mechanism was discussed by isothermal adsorption model. The results showed that the corrosion efficiency of methionine derivative was about 90%, which indicated it had excellent inhibitory effect for A3 steel in H2SO4 medium. Polarization curves indicated the inhibitor acts as mixed-type inhibitor. Impedance testing showed that the corrosion rate is decreased by increasing the charge transfer resistance of metal surface.
A novel methionine derivative pickling corrosion inhibitor was synthesized. Its structure was identified by IR and NMR. The corrosion inhibition performance of methionine derivative were studied by weight loss and electrochemical methods for A3 steel in 0.5mol·L-1 sulfuric acid medium, and the inhibition mechanism was discussed by isothermal adsorption model. The results showed that the corrosion efficiency of methionine derivative was about 90%, which indicated it had excellent inhibitory effect for A3 steel in H2SO4 medium. Polarization curves indicated the inhibitor acts as mixed-type inhibitor. Impedance testing showed that the corrosion rate is decreased by increasing the charge transfer resistance of metal surface.
