La_(2)O_(3) catalyzed oxidative coupling of methane(OCM) is a promising process that converts methane directly to valuable C_(2)(ethylene and ethane) products. Our online MS transient study results indicate that prist...La_(2)O_(3) catalyzed oxidative coupling of methane(OCM) is a promising process that converts methane directly to valuable C_(2)(ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C_(2) products, and a lower light-off temperature as well. Further study is focused on carbonate-free La_(2)O_(3) catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 e V correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results,DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexacoordinate lattice oxygen sites, with energy 2.18 e V lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C_(2) products selectivity in OCM over La_(2)O_(3) catalyst.展开更多
Rational construction of high-efficiency electrocatalysts for oxygen evolution reaction(OER)is critical for renewable-energy technologies,but it is highly challenging to rationally regulate their surface structures to...Rational construction of high-efficiency electrocatalysts for oxygen evolution reaction(OER)is critical for renewable-energy technologies,but it is highly challenging to rationally regulate their surface structures to improve the OER performance.Herein,we proposed a“model-etching”strategy to investigate chemical etching of CO_(3)O_(4).The cubic CO_(3)O_(4)nanocrystals enclosed by well-defined facets are synthesized as model crystals,whose uniform surface structures allow us to study the etching mechanism at atomic level.Etching kinetics study together with DFT calculations discloses that{111}facets,the highly active facets for OER,serve as etch-stop facets in the etching reaction and H_(2)SO_(4)molecules play a special role in creating surface Co2^(+),the active center of OER.These results direct us to rationally optimize the surface structures of CO_(3)O_(4) to develop highly active OER electrocatalysts.The favorable performance of overpotential(η)and the Tafel slope decrease even to 268 mV@10 mA·cm−2 and 74 mV·dec−1,respectively.In general,our study shows that chemical etching of model crystals could help us rationally construct high-efficiency electrocatalysts.展开更多
基金the Key Projects of Shanghai Science and Technology Commission (18JC1412100)the National Natural Science Foundation of China (No. 91745105, 22072092, 92045301)+2 种基金the startup funding provided by Shanghai Tech University for funding their participation in this workfunding provided through The Shell Foundation Grants (No. PT66201)the support from Analytical Instrumentation Center (contract no. SPSTAIC10112914), SPST, Shanghai Tech University。
文摘La_(2)O_(3) catalyzed oxidative coupling of methane(OCM) is a promising process that converts methane directly to valuable C_(2)(ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C_(2) products, and a lower light-off temperature as well. Further study is focused on carbonate-free La_(2)O_(3) catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 e V correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results,DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexacoordinate lattice oxygen sites, with energy 2.18 e V lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C_(2) products selectivity in OCM over La_(2)O_(3) catalyst.
基金This work was supported by the National Natural Science Foundation of China(Nos.21802114 and 21802115)China Postdoctoral Science Foundation(No.2019M662794)+1 种基金Natural Science Foundation of Hunan Province(Nos.2017XK2048,2018JJ3501,and 2019JJ50601)Project of Education Department of Hunan Province(No.21B0141).
文摘Rational construction of high-efficiency electrocatalysts for oxygen evolution reaction(OER)is critical for renewable-energy technologies,but it is highly challenging to rationally regulate their surface structures to improve the OER performance.Herein,we proposed a“model-etching”strategy to investigate chemical etching of CO_(3)O_(4).The cubic CO_(3)O_(4)nanocrystals enclosed by well-defined facets are synthesized as model crystals,whose uniform surface structures allow us to study the etching mechanism at atomic level.Etching kinetics study together with DFT calculations discloses that{111}facets,the highly active facets for OER,serve as etch-stop facets in the etching reaction and H_(2)SO_(4)molecules play a special role in creating surface Co2^(+),the active center of OER.These results direct us to rationally optimize the surface structures of CO_(3)O_(4) to develop highly active OER electrocatalysts.The favorable performance of overpotential(η)and the Tafel slope decrease even to 268 mV@10 mA·cm−2 and 74 mV·dec−1,respectively.In general,our study shows that chemical etching of model crystals could help us rationally construct high-efficiency electrocatalysts.
