A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural featur...A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural features shows that the NCs samples are composed of few-layered graphene-like nanoflakes with controlled in situ N doping, which is attributed to the confined pyrolysis of citric acid within the interlayers of the dicyandiamide-derived g-C_3N_4 with high nitrogen contents. Evidently, the pore volumes of the NCs increased with the increasing content of dicyandiamide in the precursor. Among these samples, the NCs nanoflakes prepared with the citric acid/dicyandiamide mass ratio of 1:6, NC-6,show the highest N content of ~6.2 at%, in which pyridinic and graphitic N groups are predominant. Compared to the commercial Pt/C catalyst, the as-prepared NC-6 exhibits a small negative shift of ~66 mV at the half-wave potential, demonstrating excellent electrocatalytic activity in the oxygen reduction reaction. Moreover, NC-6 also shows better long-term stability and resistance to methanol crossover compared to Pt/C. The efficient and stable performance are attributed to the graphene-like microstructure and high content of pyridinic and graphitic doped nitrogen in the sample, which creates more active sites as well as facilitating charge transfer due to the close four-electron reaction pathway. The superior electrocatalytic activity coupled with the facile synthetic method presents a new pathway to cost-effective electrocatalysts for practical fuel cells or metal–air batteries.展开更多
Development of high performance electrocatalysts for oxygen evolution reaction (OER) in acidic media remains a challenge for direct water splitting using an electrolyzer.Recently,Ruddlesden-Popper phase Sr_(2)IrO_(4)w...Development of high performance electrocatalysts for oxygen evolution reaction (OER) in acidic media remains a challenge for direct water splitting using an electrolyzer.Recently,Ruddlesden-Popper phase Sr_(2)IrO_(4)was discovered to be an efficient OER catalyst because of its unique structure,which consists of layers of both rock salt and perovskite phases simultaneously.In this study,we prepared a series of B-site mixed,Ruddlesden-Popper phase of Sr_(2)(Ru_(x)Ir_(1-x))O_(4) and examined their electrocatalytic properties for OER in acidic media.Through partial substitution of Ru in the B-site of Ruddlesden-Popper phase materials,we achieved much enhanced OER performance for this series of Sr_(2)(Ru_(x)Ir_(1-x))O_(4)electrocatalysts,among which Sr_(2)(Ru_(0.5)Ir_(0.5))O_(4)exhibited the best catalytic activity with a current density of 8.06 m A/cm^(2) at 1.55 V and a Tafel slope of 47 m V/dec.This current density is three times higher than that of Sr_(2)Ir O_(4).The B-site mixed Sr_(2)(Ru_(0.5)Ir_(0.5))O_(4)retained good stability in acidic conditions for>24 h at 10 m A/cm^(2).A range of techniques were used to characterize the crystal and electronic structures of the Sr_(2)(Ru_(x)Ir_(1-x))O_(4)samples.Our data indicate that the improved OER performance can be correlated to the formation of high level of hydroxyl groups and the enhanced overlap between Ir/Ru 4d and O_(2)p orbitals,revealing a new way for the design of efficient OER electrocatalysts by regulating their composition and electronic structures.展开更多
Improving the emission performance of colloidal quantum dots(QDs)is of paramount importance for their applications on light-emitting diodes(LEDs),displays and lasers.A highly promising approach is to tune the carrier ...Improving the emission performance of colloidal quantum dots(QDs)is of paramount importance for their applications on light-emitting diodes(LEDs),displays and lasers.A highly promising approach is to tune the carrier recombination channels and lifetime by exploiting the energy transfer process.However,to achieve this precise emission optimization,quantitative modulation on energy transfer efficiency is highly desirable but still challenging.Here,we demonstrate a convenient approach to realize tunable energy transfer efficiency by forming QDs mixture with controllable donor/acceptor(D/A)ratio.With the mixing ratio ranging from 16/1 to 1/16,the energy transfer efficiency could be effectively tuned from near zero to~70%.For the high mixing ratio of 16/1,acceptors obtain adequate energy supplied by closely surrounding donors,leading to~2.4-fold PL enhancement.While for the low mixing ratio,the ultrafast and efficient energy extraction process directly suppresses the multi-exciton and Auger recombination in the donor,bringing about a higher threshold.The facile modulation of emission performance by controllably designed mixing ratio and quantitatively tunable energy transfer efficiency will facilitate QD-based optoelectronic and photovoltaic applications.展开更多
基金the financial support from the National Key Research and Development Program of China (2016YFB0700204)Natural Science Foundation of Jiangsu Province (No. BK20140472)+2 种基金NSFC (51602332, 51502327)Science and Technology Commission of Shanghai Municipality (15520720400, 15YF1413800, 14DZ2261203, 16DZ2260603)One Hundred Talent Plan of Chinese Academy of Sciences
文摘A series of N-doped carbon materials(NCs)were synthesized by using biomass citric acid and dicyandiamide as renewable raw materials via a facile onestep pyrolysis method. The characterization of microstructural features shows that the NCs samples are composed of few-layered graphene-like nanoflakes with controlled in situ N doping, which is attributed to the confined pyrolysis of citric acid within the interlayers of the dicyandiamide-derived g-C_3N_4 with high nitrogen contents. Evidently, the pore volumes of the NCs increased with the increasing content of dicyandiamide in the precursor. Among these samples, the NCs nanoflakes prepared with the citric acid/dicyandiamide mass ratio of 1:6, NC-6,show the highest N content of ~6.2 at%, in which pyridinic and graphitic N groups are predominant. Compared to the commercial Pt/C catalyst, the as-prepared NC-6 exhibits a small negative shift of ~66 mV at the half-wave potential, demonstrating excellent electrocatalytic activity in the oxygen reduction reaction. Moreover, NC-6 also shows better long-term stability and resistance to methanol crossover compared to Pt/C. The efficient and stable performance are attributed to the graphene-like microstructure and high content of pyridinic and graphitic doped nitrogen in the sample, which creates more active sites as well as facilitating charge transfer due to the close four-electron reaction pathway. The superior electrocatalytic activity coupled with the facile synthetic method presents a new pathway to cost-effective electrocatalysts for practical fuel cells or metal–air batteries.
基金supported in part by the US National Science Foundation(NSF-2055734)a start-up fund from University of Illinois at Urbana-Champaignthe support of a scholarship from the China Scholarship Council(CSC)。
文摘Development of high performance electrocatalysts for oxygen evolution reaction (OER) in acidic media remains a challenge for direct water splitting using an electrolyzer.Recently,Ruddlesden-Popper phase Sr_(2)IrO_(4)was discovered to be an efficient OER catalyst because of its unique structure,which consists of layers of both rock salt and perovskite phases simultaneously.In this study,we prepared a series of B-site mixed,Ruddlesden-Popper phase of Sr_(2)(Ru_(x)Ir_(1-x))O_(4) and examined their electrocatalytic properties for OER in acidic media.Through partial substitution of Ru in the B-site of Ruddlesden-Popper phase materials,we achieved much enhanced OER performance for this series of Sr_(2)(Ru_(x)Ir_(1-x))O_(4)electrocatalysts,among which Sr_(2)(Ru_(0.5)Ir_(0.5))O_(4)exhibited the best catalytic activity with a current density of 8.06 m A/cm^(2) at 1.55 V and a Tafel slope of 47 m V/dec.This current density is three times higher than that of Sr_(2)Ir O_(4).The B-site mixed Sr_(2)(Ru_(0.5)Ir_(0.5))O_(4)retained good stability in acidic conditions for>24 h at 10 m A/cm^(2).A range of techniques were used to characterize the crystal and electronic structures of the Sr_(2)(Ru_(x)Ir_(1-x))O_(4)samples.Our data indicate that the improved OER performance can be correlated to the formation of high level of hydroxyl groups and the enhanced overlap between Ir/Ru 4d and O_(2)p orbitals,revealing a new way for the design of efficient OER electrocatalysts by regulating their composition and electronic structures.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52025023,51991342,52021006,11888101,and 61922028)the Key R&D Program of Guangdong Province,China(Grant Nos.2020B010189001,2019B010931001,and 2018B030327001)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33000000)Beijing Natural Science Foundation,China(Grant No.JQ19004)the Pearl River Talent Recruitment Program of Guangdong Province,China(Grant No.2019ZT08C321)China Postdoctoral Science Foundation(Grant No.2021T140022)。
文摘Improving the emission performance of colloidal quantum dots(QDs)is of paramount importance for their applications on light-emitting diodes(LEDs),displays and lasers.A highly promising approach is to tune the carrier recombination channels and lifetime by exploiting the energy transfer process.However,to achieve this precise emission optimization,quantitative modulation on energy transfer efficiency is highly desirable but still challenging.Here,we demonstrate a convenient approach to realize tunable energy transfer efficiency by forming QDs mixture with controllable donor/acceptor(D/A)ratio.With the mixing ratio ranging from 16/1 to 1/16,the energy transfer efficiency could be effectively tuned from near zero to~70%.For the high mixing ratio of 16/1,acceptors obtain adequate energy supplied by closely surrounding donors,leading to~2.4-fold PL enhancement.While for the low mixing ratio,the ultrafast and efficient energy extraction process directly suppresses the multi-exciton and Auger recombination in the donor,bringing about a higher threshold.The facile modulation of emission performance by controllably designed mixing ratio and quantitatively tunable energy transfer efficiency will facilitate QD-based optoelectronic and photovoltaic applications.
