The electrochemical CO_(2) reduction reaction(CO_(2)RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogendoped c...The electrochemical CO_(2) reduction reaction(CO_(2)RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogendoped carbon xerogel(Cu-N-C) are successfully developed varying the copper amount and the nature of the copper precursor, for the efficient CO_(2)RR. The electrocatalytic performance of Cu-N-C materials is assessed by a rotating ring-disc electrode(RRDE), technique still rarely explored for CO_(2)RR. For comparison, products are also characterized by online gas chromatography in a H-cell. The as-synthesized Cu-NC catalysts are found to be active and highly CO selective at low overpotentials(from -0.6 to -0.8 V vs.RHE) in 0.1 M KHCO_(3), while H_(2) from the competitive water reduction appears at larger overpotentials(-0.9 V vs. RHE). The optimum copper acetate-derived catalyst containing Cu-N_(4) moieties exhibits a CO_(2)-to-CO turnover frequency of 997 h^(-1) at -0.9 V vs. RHE with a H_(2)/CO ratio of 1.8. These results demonstrate that RRDE configuration can be used as a feasible approach for identifying electrolysis products from CO_(2)RR.展开更多
Air-coupled ultrasonic transducers(ACUTs)have been applied in industrial non-destructive testing,structural health monitoring,and medical ultrasound.However,conventional passive focusing methods often result in undesi...Air-coupled ultrasonic transducers(ACUTs)have been applied in industrial non-destructive testing,structural health monitoring,and medical ultrasound.However,conventional passive focusing methods often result in undesired effects on sensitivity due to variations in acoustic impedance matching conditions,which are critical in ACUT design,where sensitivity is the top priority.Accordingly,a novel active focusing method for ACUTs is proposed in this study.The key idea is to create multiple concentric ring electrode patterns on a bulk planar piezoelectric plate so that a quarter-wavelength acoustic impedance matching layer of uniform thickness can be attached onto the plate.The initial structural parameters of the electrode patterns are determined based on the design methodology of a Fresnel zone plate(FZP).Those parameters are optimized through finite element simulation,with the transducer’s sensitivity as the objective function,while ensuring only slight variations to the focal length and lateral resolution.Single-sided multiple concentric ring electrode patterns are then fabricated on 1-3 piezoelectric fiber/epoxy resin composite plate by screen printing and combined with a high-performance acoustic impedance matching layer made from epoxy resin composite filled with hollow glass microspheres.The planar active focusing ACUT is developed,while two types of conventional passive focusing ACUTs using FZP and concave lens are fabricated with the same piezoelectric and acoustic matching materials.Comparative experimental testing is carried out.The developed planar active-focusing ACUT achieves significant sensitivity improvements of 7.1 and 17.4dB,respectively,while maintaining comparable radial and axial full-width at half maximum.The results of this study offer a novel approach for the design of high-performance ACUTs.展开更多
Hydrogen evolution reaction(HER)is unavoidable in many electrochemical synthesis systems,such as CO_(2)reduction,N2reduction,and H_(2)O_(2)synthesis.It makes those electrochemical reactions with multiple electron-prot...Hydrogen evolution reaction(HER)is unavoidable in many electrochemical synthesis systems,such as CO_(2)reduction,N2reduction,and H_(2)O_(2)synthesis.It makes those electrochemical reactions with multiple electron-proton transfers more complex when determining kinetics and mass transfer information.Understanding how HER competes with other electrochemical reduction reactions is crucial for both fundamental studies and system performance improvements.In this study,we employed the oxygen reduction reaction(ORR)as a model reaction to investigate HER competition on a polycrystalline-Au surface,using a rotating ring and disk electrode.It’s proved that water molecules serve as the proton source for ORR in alkaline,neutral,and even acidic electrolytes,and a 4-electron process can be achieved when the overpotential is sufficiently high.The competition from H⁺reduction becomes noticeable at the H⁺concentration higher than 2 mmol L^(–1)and intensi-fies as the H^(+)concentration increases.Based on the electrochemical results,we obtained an equivalent circuit diagram for the ORR system with competition from the H+reduction reaction,showing that these reactions occur in parallel and compete with each other.Electrochemical impedance spectroscopy measurements further confirm this argument.Additionally,we discover that the contribution of H+mass transfer to the total H^(+)reduction current is significant and comparable to the kinetic current.We believe this work will deepen our understanding of HER and its competition in electrochemical reduction systems.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
The phenomenon of liquid metal“heartbeat”oscillation presents intriguing applications in microfluidic devices,drug delivery,andminiature robotics.However,achieving high vibrational kinetic energy outputs in these sy...The phenomenon of liquid metal“heartbeat”oscillation presents intriguing applications in microfluidic devices,drug delivery,andminiature robotics.However,achieving high vibrational kinetic energy outputs in these systems remains challenging.In this study,we developed a graphite ring electrode with V-shaped inner wall that enables wide-ranging control over the oscillation performance based on droplet size and the height of the V-shape.The mechanism driving the heartbeat is defined as a dynamic process involving the transformation of the oxide layer.Through electrochemical analysis,we confirmed three distinct states of the heartbeat and introduced a novel model to elucidate the role of the V-shaped structure in initiating and halting the oscillations.A comprehensive series of experiments explored how various factors,such as droplet volume,voltage,tilt angle,and V-shape height,affect heartbeat performance,achieving a significant conversion from surface energy to vibrational kinetic energy as high as 4732 J m^(-2) s^(-1).The increase in energy output is attributed to the synergistic effect of the V-shape height and droplet size on the oscillations.These results not only advance our understanding of liquidmetal droplet manipulation but also pave the way for designing high-speed microfluidic pumping systems.展开更多
基金Grant PID2020-115848RB-C21 "STORELEC" projectTED2021-129694B-C22 "DEFY-CO2" project funded by MCIN/AEI/10.13039/501100011033+3 种基金LMP253_ (2)1 project funded by Gobierno de AragónGrant IJC2019-041874-I funded by the MCIN/AEI/10.13039/501100011033CSIC for her JAE Intro ICU 2021-ICB-04 grantthe Y2020/EMT-6419 "CEOTRES" project funded by the Comunidad Autonoma de Madrid。
文摘The electrochemical CO_(2) reduction reaction(CO_(2)RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogendoped carbon xerogel(Cu-N-C) are successfully developed varying the copper amount and the nature of the copper precursor, for the efficient CO_(2)RR. The electrocatalytic performance of Cu-N-C materials is assessed by a rotating ring-disc electrode(RRDE), technique still rarely explored for CO_(2)RR. For comparison, products are also characterized by online gas chromatography in a H-cell. The as-synthesized Cu-NC catalysts are found to be active and highly CO selective at low overpotentials(from -0.6 to -0.8 V vs.RHE) in 0.1 M KHCO_(3), while H_(2) from the competitive water reduction appears at larger overpotentials(-0.9 V vs. RHE). The optimum copper acetate-derived catalyst containing Cu-N_(4) moieties exhibits a CO_(2)-to-CO turnover frequency of 997 h^(-1) at -0.9 V vs. RHE with a H_(2)/CO ratio of 1.8. These results demonstrate that RRDE configuration can be used as a feasible approach for identifying electrolysis products from CO_(2)RR.
基金supported by the National Natural Science Foundation of China(Grant No.52205564)the Foundation of Natural Science Foundation of Hubei Province,China(Grant No.2022CFB898).
文摘Air-coupled ultrasonic transducers(ACUTs)have been applied in industrial non-destructive testing,structural health monitoring,and medical ultrasound.However,conventional passive focusing methods often result in undesired effects on sensitivity due to variations in acoustic impedance matching conditions,which are critical in ACUT design,where sensitivity is the top priority.Accordingly,a novel active focusing method for ACUTs is proposed in this study.The key idea is to create multiple concentric ring electrode patterns on a bulk planar piezoelectric plate so that a quarter-wavelength acoustic impedance matching layer of uniform thickness can be attached onto the plate.The initial structural parameters of the electrode patterns are determined based on the design methodology of a Fresnel zone plate(FZP).Those parameters are optimized through finite element simulation,with the transducer’s sensitivity as the objective function,while ensuring only slight variations to the focal length and lateral resolution.Single-sided multiple concentric ring electrode patterns are then fabricated on 1-3 piezoelectric fiber/epoxy resin composite plate by screen printing and combined with a high-performance acoustic impedance matching layer made from epoxy resin composite filled with hollow glass microspheres.The planar active focusing ACUT is developed,while two types of conventional passive focusing ACUTs using FZP and concave lens are fabricated with the same piezoelectric and acoustic matching materials.Comparative experimental testing is carried out.The developed planar active-focusing ACUT achieves significant sensitivity improvements of 7.1 and 17.4dB,respectively,while maintaining comparable radial and axial full-width at half maximum.The results of this study offer a novel approach for the design of high-performance ACUTs.
文摘Hydrogen evolution reaction(HER)is unavoidable in many electrochemical synthesis systems,such as CO_(2)reduction,N2reduction,and H_(2)O_(2)synthesis.It makes those electrochemical reactions with multiple electron-proton transfers more complex when determining kinetics and mass transfer information.Understanding how HER competes with other electrochemical reduction reactions is crucial for both fundamental studies and system performance improvements.In this study,we employed the oxygen reduction reaction(ORR)as a model reaction to investigate HER competition on a polycrystalline-Au surface,using a rotating ring and disk electrode.It’s proved that water molecules serve as the proton source for ORR in alkaline,neutral,and even acidic electrolytes,and a 4-electron process can be achieved when the overpotential is sufficiently high.The competition from H⁺reduction becomes noticeable at the H⁺concentration higher than 2 mmol L^(–1)and intensi-fies as the H^(+)concentration increases.Based on the electrochemical results,we obtained an equivalent circuit diagram for the ORR system with competition from the H+reduction reaction,showing that these reactions occur in parallel and compete with each other.Electrochemical impedance spectroscopy measurements further confirm this argument.Additionally,we discover that the contribution of H+mass transfer to the total H^(+)reduction current is significant and comparable to the kinetic current.We believe this work will deepen our understanding of HER and its competition in electrochemical reduction systems.
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.
基金National Natural Science Foundation of China,Grant/Award Number:51901009。
文摘The phenomenon of liquid metal“heartbeat”oscillation presents intriguing applications in microfluidic devices,drug delivery,andminiature robotics.However,achieving high vibrational kinetic energy outputs in these systems remains challenging.In this study,we developed a graphite ring electrode with V-shaped inner wall that enables wide-ranging control over the oscillation performance based on droplet size and the height of the V-shape.The mechanism driving the heartbeat is defined as a dynamic process involving the transformation of the oxide layer.Through electrochemical analysis,we confirmed three distinct states of the heartbeat and introduced a novel model to elucidate the role of the V-shaped structure in initiating and halting the oscillations.A comprehensive series of experiments explored how various factors,such as droplet volume,voltage,tilt angle,and V-shape height,affect heartbeat performance,achieving a significant conversion from surface energy to vibrational kinetic energy as high as 4732 J m^(-2) s^(-1).The increase in energy output is attributed to the synergistic effect of the V-shape height and droplet size on the oscillations.These results not only advance our understanding of liquidmetal droplet manipulation but also pave the way for designing high-speed microfluidic pumping systems.
