Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation comp...Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation.In this work,calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces(001)and(010)of nickel oxide hydroxide(NiOOH).Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process.The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH.By contrast,the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation.These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.展开更多
An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeO...An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeOOH,show promising OER reactivity.In the present work,we performed a DFT+U study of the OER mechanism on theγ‐FeOOH(010)surface.In particular,we established the chemical potential of the OH?and hole pair and included the OH?anion in the reaction pathway,accounting to the alkaline conditions of anodic OER process.We then analyzed the OER pathways on the surface with OH‐,O‐and Fe‐terminations.On the surface with OH‐and O‐terminations,the O2molecule could form from either OH reacting with the surface oxygen species(-OH*and-O*)or the combination of two surface oxygen species.On the Fe‐terminated surface,O2can only form by adsorbing OH on the Fe sites first.The potential‐limiting step of the oxygen evolution with different surface terminations was determined by following the free‐energy change of the elementary steps along each pathway.Our results show that oxygen formation requires recreating the surface Fe sites,and consequently,the condition that favors the partially exposed Fe sites will promote oxygen formation.展开更多
The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemical...The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemicals and fuels.However,this reaction is mildly endothermic and competed by a strongly exothermic CO2 methanation reaction at low temperatures.Therefore,the improvement in the low-temperature activities and selectivity of the RWGS reaction is a key challenge for catalyst designs.We reviewed recent advances in the design strategies of supported metal catalysts for enhancing the activity of CO2 conversion and its selectivity to CO.These strategies include varying support,tuning metal–support interactions,adding reducible transition metal oxide promoters,forming bimetallic alloys,adding alkali metals,and enveloping metal particles.These advances suggest that enhancing CO2 adsorption and facilitating CO desorption are key factors to enhance CO2 conversion and CO selectivity.This short review may provide insights into future RWGS catalyst designs and optimization.展开更多
Carbon-supported nanocomposites are attracting particular attention as high-performance,low-cost electrocatalysts for electrochemical water splitting.These are mostly prepared by pyrolysis and hydrothermal procedures ...Carbon-supported nanocomposites are attracting particular attention as high-performance,low-cost electrocatalysts for electrochemical water splitting.These are mostly prepared by pyrolysis and hydrothermal procedures that are time-consuming(from hours to days)and typically difficult to produce a nonequilibrium phase.Herein,for the first time ever,we exploit magnetic induction heating-quenching for ultrafast production of carbon-FeNi spinel oxide nanocomposites(within seconds),which exhibit an unprecedentedly high performance towards oxygen evolution reaction(OER),with an ultralow overpotential of only+260 mV to reach the high current density of 100 mA cm^(-2).Experimental and theoretical studies show that the rapid heating and quenching process(ca.10^(3)K s^(-1))impedes the Ni and Fe phase segregation and produces a Cl-rich surface,both contributing to the remarkable catalytic activity.Results from this study highlight the unique advantage of ultrafast heating/quenching in the structural engineering of functional nanocomposites to achieve high electrocatalytic performance towards important electrochemical reactions.展开更多
Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of...Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of^180 nm were initially synthesized.Thereafter,Cu2O was used as a sacrificial template to prepare a series of Ag/Cu2O composites through galvanic replacement.By varying the Ag/Cu atomic ratio,Ago.12/Cu2O,having a hierarchical,flower-like nanostructure with intersecting Ag nanoflakes encompassing an inner Cu2O sphere,was prepared.The as-prepared Ag/Cu2O samples presented higher Faradaic efficiencies(FE)for CO and relatively suppressed H2 evolution than the parent Cu2O nanospheres due to the combination of Ag with Cu2O in the former.Notably,the highest CO evolution rate was achieved with Ago.12/Cu2O due to the larger electroactive surface area furnished by the hierarchical structure.The same hier-archical flower-like structure was also obtained for the Auo./Cu2O composite,where the FEco(10%)was even higher than that of Ago.12/Cu2O.Importantly,the results reveal that Ago.12/Cu2O and Auo./Cu2O both exhibit remarkably improved stability relative to Cu2O.This study presents a facile method of developing hierarchical metal-oxide composites as fficient and stable electrocatalysts for the electrochemical reduction of CO2.展开更多
The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independen...The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independent CO/H_(2) ratio are highly desired.Herein,a series of N-doped carbon nanotubes encapsulating binary alloy nanoparticles(MxNi-NCNT,M=Fe,Co)were successfully fabricated through the co-pyrolysis of melamine and metal precursors.The MxNi-NCNT samples exhibited bamboo-like nanotubular structures with a large specific surface area and high degree of graphitization.Their electrocatalytic performance for syngas production can be tuned by changing the alloy compositions and modifying the electronic structure of the carbon nanotube through the encapsulated metal nanoparticles.Consequently,syngas with a wide range of CO/H_(2) ratios,from 0.5:1 to 3.4:1,can be produced on MxNi-NCNT.More importantly,stable CO/H_(2) ratios of 2:1 and 1.5:1,corresponding to the ratio to produce biofuels by syngas fermentation,could be realized on Co1Ni-NCNT and Co2Ni-NCNT,respectively,over a potential window of-0.8 to-1.2 V versus the reversible hydrogen electrode.Our work provides an approach to develop low-cost and potential-independent electrocatalysts to effectively produce syngas with an adjustable CO/H_(2) ratio from electrochemical CO_(2) reduction.展开更多
Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfa...Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfaces based on the results of density functional theory slab calculations. We mapped out the potential energy profiles for electrochemical reduction of CO2 to formate and other possible products on both surfaces. Our results show that the first step is the formation of the adsorbed formate(HCOO*) species through an Eley-Rideal mechanism. The formate species can be reduced to HCOO- through a oneelectron reduction in basic solution, which produces formic acid as the predominant product. The respective potentials of forming HCOO* are predicted to be -0.72 and -0.58 V on Pb and Sn. Higher overpotentials make other reaction pathways accessible, leading to different products. On Sn(112), CO and CH4 can be generated at -0.65 V following formate formation. In contrast, the limiting potential to access alternative reaction channels on Pb(211) is -1.33 V, significantly higher than that of Sn.展开更多
基金the National Natural Science Foundation of China(Nos.21873067 and 21576204).
文摘Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation.In this work,calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces(001)and(010)of nickel oxide hydroxide(NiOOH).Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process.The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH.By contrast,the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation.These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.
基金supported by the Chemical,Biological,Environmental,and Transport Systems(CBET)program of US National Science Foundation(CBET-1438440)~~
文摘An efficient and economical oxygen evolution reaction(OER)catalyst is critical to the widespread application of solar energy to fuel conversion.Among many potential OER catalysts,the metal oxyhydroxides,especially FeOOH,show promising OER reactivity.In the present work,we performed a DFT+U study of the OER mechanism on theγ‐FeOOH(010)surface.In particular,we established the chemical potential of the OH?and hole pair and included the OH?anion in the reaction pathway,accounting to the alkaline conditions of anodic OER process.We then analyzed the OER pathways on the surface with OH‐,O‐and Fe‐terminations.On the surface with OH‐and O‐terminations,the O2molecule could form from either OH reacting with the surface oxygen species(-OH*and-O*)or the combination of two surface oxygen species.On the Fe‐terminated surface,O2can only form by adsorbing OH on the Fe sites first.The potential‐limiting step of the oxygen evolution with different surface terminations was determined by following the free‐energy change of the elementary steps along each pathway.Our results show that oxygen formation requires recreating the surface Fe sites,and consequently,the condition that favors the partially exposed Fe sites will promote oxygen formation.
基金the National Key Research and Development Program of China(No.2016YFB0600900)the National Natural Science Foundation of China(Nos.21676194 and 21873067)for their support。
文摘The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemicals and fuels.However,this reaction is mildly endothermic and competed by a strongly exothermic CO2 methanation reaction at low temperatures.Therefore,the improvement in the low-temperature activities and selectivity of the RWGS reaction is a key challenge for catalyst designs.We reviewed recent advances in the design strategies of supported metal catalysts for enhancing the activity of CO2 conversion and its selectivity to CO.These strategies include varying support,tuning metal–support interactions,adding reducible transition metal oxide promoters,forming bimetallic alloys,adding alkali metals,and enveloping metal particles.These advances suggest that enhancing CO2 adsorption and facilitating CO desorption are key factors to enhance CO2 conversion and CO selectivity.This short review may provide insights into future RWGS catalyst designs and optimization.
基金This work was supported by grants from the National Science Foundation(CHE-1900235 and CHE-2003685,S.W.C.and CHE-1900401,H.L.X.)Part of the TEM and XPS work was carried out at the National Center for Electron Microscopy and Molecular Foundry,Lawrence Berkeley National Laboratory,which is supported by the Office of Science,Office of Basic Energy Sciences,of U.S.Department of Energy under Contract No.DE-AC02-05CH11231,as part of a user project.The XAS work used resources of the Advanced Photon Source,a User Facility operated for the U.S.Department of Energy(DOE)Office of Science by Argonne National Laboratory and was supported by the DOE under contract No.DE-AC02-06CH11357 and the Canadian Light Source and its funding partners+1 种基金This research also used resources of the Center for Functional Nanomaterials(CFN),which is a U.S.Department of Energy Office of Science User Facility,at Brookhaven National Laboratory under Contract No.DE-SC0012704The authors also thank Mr.Jeremy Barnett for the assistance in sample preparation and data acquisition of X-ray diffraction measurements in the UCSC X-ray Facility which was funded by the National Science Foundation(MRI-1126845).
文摘Carbon-supported nanocomposites are attracting particular attention as high-performance,low-cost electrocatalysts for electrochemical water splitting.These are mostly prepared by pyrolysis and hydrothermal procedures that are time-consuming(from hours to days)and typically difficult to produce a nonequilibrium phase.Herein,for the first time ever,we exploit magnetic induction heating-quenching for ultrafast production of carbon-FeNi spinel oxide nanocomposites(within seconds),which exhibit an unprecedentedly high performance towards oxygen evolution reaction(OER),with an ultralow overpotential of only+260 mV to reach the high current density of 100 mA cm^(-2).Experimental and theoretical studies show that the rapid heating and quenching process(ca.10^(3)K s^(-1))impedes the Ni and Fe phase segregation and produces a Cl-rich surface,both contributing to the remarkable catalytic activity.Results from this study highlight the unique advantage of ultrafast heating/quenching in the structural engineering of functional nanocomposites to achieve high electrocatalytic performance towards important electrochemical reactions.
基金We are grateful to the Analysis and Test Center of Tianjin University for providing XRD,SEM,and TEM characterization.We also acknowledge the National Natural Science Foundation of China(Grant Nos.21576204 and 21206117)for financial support.
文摘Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of^180 nm were initially synthesized.Thereafter,Cu2O was used as a sacrificial template to prepare a series of Ag/Cu2O composites through galvanic replacement.By varying the Ag/Cu atomic ratio,Ago.12/Cu2O,having a hierarchical,flower-like nanostructure with intersecting Ag nanoflakes encompassing an inner Cu2O sphere,was prepared.The as-prepared Ag/Cu2O samples presented higher Faradaic efficiencies(FE)for CO and relatively suppressed H2 evolution than the parent Cu2O nanospheres due to the combination of Ag with Cu2O in the former.Notably,the highest CO evolution rate was achieved with Ago.12/Cu2O due to the larger electroactive surface area furnished by the hierarchical structure.The same hier-archical flower-like structure was also obtained for the Auo./Cu2O composite,where the FEco(10%)was even higher than that of Ago.12/Cu2O.Importantly,the results reveal that Ago.12/Cu2O and Auo./Cu2O both exhibit remarkably improved stability relative to Cu2O.This study presents a facile method of developing hierarchical metal-oxide composites as fficient and stable electrocatalysts for the electrochemical reduction of CO2.
基金funded by the National Natural Science Foundation of China(Grant Nos.21873067,21206117).
文摘The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independent CO/H_(2) ratio are highly desired.Herein,a series of N-doped carbon nanotubes encapsulating binary alloy nanoparticles(MxNi-NCNT,M=Fe,Co)were successfully fabricated through the co-pyrolysis of melamine and metal precursors.The MxNi-NCNT samples exhibited bamboo-like nanotubular structures with a large specific surface area and high degree of graphitization.Their electrocatalytic performance for syngas production can be tuned by changing the alloy compositions and modifying the electronic structure of the carbon nanotube through the encapsulated metal nanoparticles.Consequently,syngas with a wide range of CO/H_(2) ratios,from 0.5:1 to 3.4:1,can be produced on MxNi-NCNT.More importantly,stable CO/H_(2) ratios of 2:1 and 1.5:1,corresponding to the ratio to produce biofuels by syngas fermentation,could be realized on Co1Ni-NCNT and Co2Ni-NCNT,respectively,over a potential window of-0.8 to-1.2 V versus the reversible hydrogen electrode.Our work provides an approach to develop low-cost and potential-independent electrocatalysts to effectively produce syngas with an adjustable CO/H_(2) ratio from electrochemical CO_(2) reduction.
基金supported by the National Natural Sciences Foundation of China(21373148,21206117)
文摘Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfaces based on the results of density functional theory slab calculations. We mapped out the potential energy profiles for electrochemical reduction of CO2 to formate and other possible products on both surfaces. Our results show that the first step is the formation of the adsorbed formate(HCOO*) species through an Eley-Rideal mechanism. The formate species can be reduced to HCOO- through a oneelectron reduction in basic solution, which produces formic acid as the predominant product. The respective potentials of forming HCOO* are predicted to be -0.72 and -0.58 V on Pb and Sn. Higher overpotentials make other reaction pathways accessible, leading to different products. On Sn(112), CO and CH4 can be generated at -0.65 V following formate formation. In contrast, the limiting potential to access alternative reaction channels on Pb(211) is -1.33 V, significantly higher than that of Sn.
