Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa...Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa,app decreases with φ, while pre-exponential factor A remains nearly unchanged,which conforms well the prediction from Butler-Volmer equation. In contrast, with φ nega-tive shifts from the onset potential for HER to the potential of zero charge （PZC≈-0.4 V）, both Ea,app and A for HER increase （e.g., Ea,app increases from 24 kJ/mol to 32 kJ/mol）. The increase in Ea,app and A with negative shift in φ from -0.25 V to PZC is explained by the increases of both internal energy change and entropy change from reactants to the transition states, which is correlated with the change in the hydrogen bond network during HER. The positive entropy effects overcompensate the adverse effect from the increase in the activation energy, which leads to a net increase in HER current with the activation energy negative shift from the onset potential of HER to PZC. It is pointed out that entropy change may contribute greatly to the kinetics for electrode reaction which involves the transfer of electron and proton, such as HER.展开更多
The temperature dependence of hydrogen evolution reaction （HER） at a quasi-single crystalline gold electrode in both 0.1 mol/L HCl04 and 0.1 mol/L KOH solutions was investigated by cyclic voltammetry. HER current di...The temperature dependence of hydrogen evolution reaction （HER） at a quasi-single crystalline gold electrode in both 0.1 mol/L HCl04 and 0.1 mol/L KOH solutions was investigated by cyclic voltammetry. HER current displays a clear increase with reaction overpotential （η） and temperature from 278-333 K. In 0.1 mol/L HClO4 the Tafel slopes are found to increases slightly with temperature from 118 mV/dec to 146 mV/dec, while in 0.1 mol/L KOH it is ca. 153±15 mV/dec without clear temperature-dependent trend. The apparent activation energy （Ea） for HER at equilibrium potential is ca. 48 and 34 kJ/mol in 0.1 mol/L HC104 and 0.1 mol/L KOH, respectively. In acid solution, Ea decreases with increase in η, from Ea-37 kJ/mol （η=0.2 V） to 30 kJ/mol （η=0.35 V）. In contrast, in 0.1 mol/L KOH, Ea does not show obvious change with U. The pre-exponential factor （A） in 0.1 mol/L HC104 is ca. 1 order higher than that in 0.1 mol/L KOH. Toward more negative potential, in 0.1 mol/L HC104 A changes little with potential, while in 0.1 mol/L KOH it displays a monotonic increase with U. The change trends of the potential-dependent kinetic parameters for HER at Au electrode in 0.1 mol/L HClO4 and that in 0.1 mol/L KOH are discussed.展开更多
Among all the DNA components, extremely redox-active guanine （G） and adenine （A） bases are subject to facile loss of an electron and form cation radicals （G＋＂ and A＋＇） when exposed to irradiation or radical ...Among all the DNA components, extremely redox-active guanine （G） and adenine （A） bases are subject to facile loss of an electron and form cation radicals （G＋＂ and A＋＇） when exposed to irradiation or radical oxidants. The subsequent deprotonation of G＋＇ and A＋＇ can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G＋, studies on the deprotonation of A＋ are still limited at present. Herein, we investigate the deprotonation behavior of A＋. by time-resolved laser flash photolysis. The deprotonation product of A（N6-H）＇ is observed and the deprotonation rate constant, （2.0±0.1）×10 7 s-1, is obtained at room temperature. Further, the deprotonation rate con- stants of A＋. are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N6-H deprotonation is determined to be （17.1±1.0） kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A＋ deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A＋ in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.展开更多
Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate conditi...Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy Ea of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35-0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1-1.69 times as temperature increase every 10 ℃ at the temperature range of 10 to 60 ℃.展开更多
To investigate the reaction between CO2-CO and wustite using the isotope exchange method at 1073, 1173, 1273, and 1373 K, the experiment apparatus was designed to simulate the fluidized bed. The chemical rate constant...To investigate the reaction between CO2-CO and wustite using the isotope exchange method at 1073, 1173, 1273, and 1373 K, the experiment apparatus was designed to simulate the fluidized bed. The chemical rate constant was estimated by considering the effect of gas phase mass transfer on the reaction. It is found that the chemical rate constant is inversely decreased with the increase in the ratio of CO2/CO by volume. The activation energy of reaction is in a linear relationship with the ratio of COs/CO by volume, and the average activation energy is 155.37 kJ/mol.展开更多
The dimensions and the materials type limit the performance of fuel cell. The increase of the temperature in electrodes and electrolyte of the cell,is due to the over potential of activation (transfer of load),the ove...The dimensions and the materials type limit the performance of fuel cell. The increase of the temperature in electrodes and electrolyte of the cell,is due to the over potential of activation (transfer of load),the over potential Ohmic (resistance of polarization),the over potential of reaction (heat released by the chemical reaction) and the over potential of diffusion. In this paper,we studied the thermo-electrical performance of an intermediate temperature solid oxide fuel cell (IT-SOFC) with electrode supported. The aim of this work is to study this increasing temperature of a single cell of an IT-SOFC under the influence of the following parameters: heat sources,functioning temperature and voltages of the cell,geometric configuration and materials type. The equation of energy in one dimension is numerically resolved by using the method of finite volumes. A computing program (FORTRAN) is developed locally for this purpose in order to obtain fields of temperature in every element of the cell.展开更多
The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects o...The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects of the three factors on urease activity(V_(0)),hydrolysis rate constant(K_(u)),and activation energy(Ea)and establishing the quantitative model for K_(u) under the coupling condition.Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃,and 35℃),moisture contents(θ)(60%,80%,and 100%of field capacities),and nitrogen application rates(F)(247 mg/kg,309 mg/kg,371 mg/kg,and 433 mg/kg).The urea content was measured daily.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on V_(0) and K_(u) were in the descending order:T,F,T^(*)F,θ,T^(*)θ,F^(*)θ,T^(*)θ^(*)F.The effect of single factor and two-factor coupling on V_(0) was extremely significant(p<0.01),whereas the effect of the three-factor coupling on V_(0) was negligible.The effects of three factors and their interaction on K_(u) were extremely significant(p<0.01).The effects of moisture content,nitrogen application rate,and their interaction on Ea were in the descending order:F,θ,F^(*)θ.The effects of two factors and their interaction on Ea were not significant.The mean absolute percentage error(MAPE)values of the established K_(u-1)(θ,T,F)and K_(u-2)(θ,T,F)models were 3.14%and 4.60%,respectively.The MAPE of the traditional Arrhenius model K_(u-3)(T)was 6.75%.The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model.The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of K_(u).展开更多
基金ACKNOWLEDGMENTS This work was supported by the One Hundred Talents＇ Program of the Chinese Academy of Science, the National Natural Science Foundation of China （No.21073176）, and the National Basic Research Program of China National Science and Technology （No.2010CB923302）.
文摘Hydrogen evolution reaction （HER） at polycrystalline silver electrode in 0.1 mol/L HClO4 solution is investigated by cyclic voltammetry in the temperature range of 278-333 K. We found that at electrode potential φa,app decreases with φ, while pre-exponential factor A remains nearly unchanged,which conforms well the prediction from Butler-Volmer equation. In contrast, with φ nega-tive shifts from the onset potential for HER to the potential of zero charge （PZC≈-0.4 V）, both Ea,app and A for HER increase （e.g., Ea,app increases from 24 kJ/mol to 32 kJ/mol）. The increase in Ea,app and A with negative shift in φ from -0.25 V to PZC is explained by the increases of both internal energy change and entropy change from reactants to the transition states, which is correlated with the change in the hydrogen bond network during HER. The positive entropy effects overcompensate the adverse effect from the increase in the activation energy, which leads to a net increase in HER current with the activation energy negative shift from the onset potential of HER to PZC. It is pointed out that entropy change may contribute greatly to the kinetics for electrode reaction which involves the transfer of electron and proton, such as HER.
基金V, ACKNOWLEDGMENTS This work was supported by one Hundred Talents＇ Program of the Chinese Academy of Science, the National Natural Science Foundation of China （No.21073176）, and 973 Program from the Ministry of Science and Technology of China （No.2010CB923302）.
文摘The temperature dependence of hydrogen evolution reaction （HER） at a quasi-single crystalline gold electrode in both 0.1 mol/L HCl04 and 0.1 mol/L KOH solutions was investigated by cyclic voltammetry. HER current displays a clear increase with reaction overpotential （η） and temperature from 278-333 K. In 0.1 mol/L HClO4 the Tafel slopes are found to increases slightly with temperature from 118 mV/dec to 146 mV/dec, while in 0.1 mol/L KOH it is ca. 153±15 mV/dec without clear temperature-dependent trend. The apparent activation energy （Ea） for HER at equilibrium potential is ca. 48 and 34 kJ/mol in 0.1 mol/L HC104 and 0.1 mol/L KOH, respectively. In acid solution, Ea decreases with increase in η, from Ea-37 kJ/mol （η=0.2 V） to 30 kJ/mol （η=0.35 V）. In contrast, in 0.1 mol/L KOH, Ea does not show obvious change with U. The pre-exponential factor （A） in 0.1 mol/L HC104 is ca. 1 order higher than that in 0.1 mol/L KOH. Toward more negative potential, in 0.1 mol/L HC104 A changes little with potential, while in 0.1 mol/L KOH it displays a monotonic increase with U. The change trends of the potential-dependent kinetic parameters for HER at Au electrode in 0.1 mol/L HClO4 and that in 0.1 mol/L KOH are discussed.
文摘Among all the DNA components, extremely redox-active guanine （G） and adenine （A） bases are subject to facile loss of an electron and form cation radicals （G＋＂ and A＋＇） when exposed to irradiation or radical oxidants. The subsequent deprotonation of G＋＇ and A＋＇ can invoke DNA damage or interrupt hole transfer in DNA. However, compared with intensive reports for G＋, studies on the deprotonation of A＋ are still limited at present. Herein, we investigate the deprotonation behavior of A＋. by time-resolved laser flash photolysis. The deprotonation product of A（N6-H）＇ is observed and the deprotonation rate constant, （2.0±0.1）×10 7 s-1, is obtained at room temperature. Further, the deprotonation rate con- stants of A＋. are measured at temperatures varying from 280 K to 300 K, from which the activation energy for the N6-H deprotonation is determined to be （17.1±1.0） kJ/mol by Arrhenius equation. In addition, by incorporating the aqueous solvent effect, we perform density functional theory calculations for A＋ deprotonation in free base and in duplex DNA. Together with experimental results, the deprotonation mechanisms of A＋ in free base and in duplex DNA are revealed, which are of fundamental importance for understanding the oxidative DNA damage and designing DNA-based electrochemical devices.
基金Funded by National Natural Science Fundation of China(No.51178455)
文摘Accelerated carbonation experiments about the development of carbonation rates of ordinary Portland cement concrete under different artificial climates were carried out. Six water cement ratios and six climate condition combinations of temperature and relative humidity were used. Results indicate that changes of concrete carbonation rate with environmental temperature agree the Arrhenius law well, which suggests concrete carbonation rate has obvious dependence on temperature. The higher the temperature is, the more quickly the concrete carbonates, and at the same time it is also affected by environmental relative humidity. Thereafter, the apparent activation energy Ea of concrete carbonation reaction was obtained, ranging from 16.8 to 20.6 kJ/mol corresponding 0.35-0.74 water cement ratio, and lower water cement ratio will cause the apparent activation energy increase. Concrete carbonation rates will increase 1.1-1.69 times as temperature increase every 10 ℃ at the temperature range of 10 to 60 ℃.
基金supported by the National Natural Science Foundation of China (Nos. 50874128 and 50834007)
文摘To investigate the reaction between CO2-CO and wustite using the isotope exchange method at 1073, 1173, 1273, and 1373 K, the experiment apparatus was designed to simulate the fluidized bed. The chemical rate constant was estimated by considering the effect of gas phase mass transfer on the reaction. It is found that the chemical rate constant is inversely decreased with the increase in the ratio of CO2/CO by volume. The activation energy of reaction is in a linear relationship with the ratio of COs/CO by volume, and the average activation energy is 155.37 kJ/mol.
文摘The dimensions and the materials type limit the performance of fuel cell. The increase of the temperature in electrodes and electrolyte of the cell,is due to the over potential of activation (transfer of load),the over potential Ohmic (resistance of polarization),the over potential of reaction (heat released by the chemical reaction) and the over potential of diffusion. In this paper,we studied the thermo-electrical performance of an intermediate temperature solid oxide fuel cell (IT-SOFC) with electrode supported. The aim of this work is to study this increasing temperature of a single cell of an IT-SOFC under the influence of the following parameters: heat sources,functioning temperature and voltages of the cell,geometric configuration and materials type. The equation of energy in one dimension is numerically resolved by using the method of finite volumes. A computing program (FORTRAN) is developed locally for this purpose in order to obtain fields of temperature in every element of the cell.
基金supported by the National Natural Science Foundation of China(No.51579168 and No.51249002)the Natural Science Foundation of Shanxi Province of China(No.201601D011053)+1 种基金the Graduate Education Innovation Program of Shanxi Province of China(No.2016BY064)the Scientific and Technological Project of Shanxi Province of China(No.20140311016-6).
文摘The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects of the three factors on urease activity(V_(0)),hydrolysis rate constant(K_(u)),and activation energy(Ea)and establishing the quantitative model for K_(u) under the coupling condition.Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃,and 35℃),moisture contents(θ)(60%,80%,and 100%of field capacities),and nitrogen application rates(F)(247 mg/kg,309 mg/kg,371 mg/kg,and 433 mg/kg).The urea content was measured daily.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on V_(0) and K_(u) were in the descending order:T,F,T^(*)F,θ,T^(*)θ,F^(*)θ,T^(*)θ^(*)F.The effect of single factor and two-factor coupling on V_(0) was extremely significant(p<0.01),whereas the effect of the three-factor coupling on V_(0) was negligible.The effects of three factors and their interaction on K_(u) were extremely significant(p<0.01).The effects of moisture content,nitrogen application rate,and their interaction on Ea were in the descending order:F,θ,F^(*)θ.The effects of two factors and their interaction on Ea were not significant.The mean absolute percentage error(MAPE)values of the established K_(u-1)(θ,T,F)and K_(u-2)(θ,T,F)models were 3.14%and 4.60%,respectively.The MAPE of the traditional Arrhenius model K_(u-3)(T)was 6.75%.The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model.The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of K_(u).
