Pt纳米颗粒在氮掺杂空心碳微球上的高分散负载及其氧还原性能

Pt 纳米颗粒在氮掺杂空心碳微球上的高分散负载及其氧还原性能张小华1,*钟金娣1,§于亚明1,§张云松2刘博3,*陈金华1,*(1湖南大学化学化工学院,化学生物传感与计量学国家重点实验室,长沙410082;2四川农业大学生命科学与理学院,四川雅安625014;3西北有色金属研究院,西安钛金工业电化学技术有限公司,西安710016)摘要:通过热解自聚合多巴胺法制备了氮掺杂空心碳微球(N-HCMS),并采用微波辅助乙二醇还原方法把Pt纳米粒子负载于N-HCMS 上制得了Pt/N-HCMS 催化剂.催化剂的表面形貌、晶体结构及其比表面积和孔径分布等分别采用扫描电子显微镜、透射电子显微镜、X 射线衍射仪及比表面分析仪等进行表征.采用循环伏安法和线性扫描伏安法研究了Pt/N-HCMS 催化剂在酸性条件下的电催化氧还原性能.Pt/N-HCMS 催化剂由于Pt 纳米粒子的均匀分散、N-HCMS 载体的快速电子传递及其独特的微孔和中空结构而具有很高的电催化氧还原活性,其质量比活性是E-TEK Pt/C 催化剂的近两倍.Pt/N-HCMS 催化剂还具有优良的稳定性.本工作对于开发高性能的燃料电池阴极催化剂具有重要意义.关键词:氮掺杂;空心碳微球;Pt 纳米粒子;电催化;氧还原反应中图分类号:O646;O643Well-Dispersed Platinum Nanoparticles Supported on Nitrogen-Doped Hollow Carbon Microspheres for Oxygen-Reduction ReactionZHANG Xiao-Hua 1,*ZHONG Jin-Di 1,§YU Ya-Ming 1,§ZHANG Yun-Song 2LIU Bo 3,*CHEN Jin-Hua 1,*(1State Key Laboratory of Chemo/Biosensing and Chemometrics,College of Chemistry and Chemical Engineering,HunanUniversity,Changsha 410082,P .R.China ;2College of Life and Science,Sichuan Agricultural University,Yaan 625014,Sichuan Province,P .R.China ;3Xi ʹan Taijin Industrial Electrochemical Technology Co.,Ltd.,Northwest Institute forNon-Ferrous Metal Research,Xi ʹan 710016,P .R.China )Abstract:Nitrogen-doped hollow carbon microspheres (N-HCMS)were synthesized by carbonization of poly(dopamine).Platinum (Pt)nanoparticles (NPs)were deposited onto the N-HCMS via a microwave-assisted reduction process.The morphology,surface area,and pore size distribution of the N-HCMS supported Pt catalysts (Pt/N-HCMS)were characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and surface area and porosimetry measurements.The electrocatalytic properties of the Pt/N-HCMS catalyst towards oxygen-reduction reaction were investigated by cyclic voltammetry and linear sweep voltammetry.The Pt/N-HCMS catalyst showed almost double the specific mass activity of a commercial carbon supported Pt catalyst.This was attributed to a uniform dispersion of the Pt NPs and the unique mesoporous and hollow structure of N-HCMS.In addition,fast electron transfer processes were found to occur on the nitrogen doped N-HCMS and the catalyst exhibited excellent[Article]doi:10.3866/PKU.WHXB201304011物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .2013,29(6),1297-1304June Received:October 25,2012;Revised:April 1,2013;Published on Web:April 1,2013.∗Corresponding authors.ZHANG Xiao-Hua,Email:mickyxie@;Tel:+86-731-88821961.LIU Bo,Email:net lb@;Tel:+86-135********.CHEN Jin-Hua,Email:chenjinhua@;Tel:+86-731-88821961.§These authors contributed equally to this work.The project was supported by the Program for Changjiang Scholars and Innovative Research Team in University,China (PCSIRT),Hunan Provincial Natural Science Foundation,China (12JJ2010),Young Teachers ʹGrowth Plan (2012),and Specialized Research Fund for the Doctoral Program of Higher Education,China (20110161110009).长江学者和创新团队发展计划(PCSIRT),湖南省自然科学基金(12JJ2010)及高等学校年轻教师成长计划(2012)和博士学科点专项科研基金(20110161110009)资助项目ⒸEditorial office of Acta Physico-Chimica Sinica1297Acta Phys.-Chim.Sin.2013Vol.29long-term stability.This work is of significance for the development of high-performance cathodiccatalysts in fuel cells.Key Words:Nitrogen-doping;Hollow carbon microsphere;Pt nanoparticle;Electrocatalysis;Oxygen-reduction reaction1IntroductionProton exchange membrane fuel cells(PEMFCs)have at-tracted great attention as an efficient power generation source with high power density and low emission for portable elec-tronic devices.1However,the problems such as sluggish kinet-ics of the oxygen reduction reaction(ORR),poor catalytic ac-tivity,and low durability of the cathodic catalysts still limit the commercial development of PEMFCs.2So,the development of highly qualified cathodic catalysts for ORR is of great impor-tance for practical application of fuel cells.3After decades of scientific research,highly dispersed Pt nanoparticles(NPs)sup-ported on carbon black(e.g.,Vulcan XC72)are recognized as the state-of-the-art commercial cathodic catalyst.However, due to corrosion of the carbon support and weak link between Pt NPs and carbon black,4the loss or agglomeration of Pt NPs in the carbon black supported Pt catalyst,which results in the degradation of catalytic performance,is still a serious problem to be addressed for promoting the practical application of PEM-FCs.In addition,the carbon black with broad pore size distribu-tion and poor pore connectivity significantly reduces the utili-zation of Pt.5Hence,more and more research efforts in fuel cell technology have focused on the development of better sup-port materials with specific morphologies and properties. Recently,hollow carbon microspheres(HCMS)with a well-defined structure of hollow core and carbon shell have been at-tracting great interest in many technical areas such as drug de-livery,active material encapsulation,lithium-ion batteries,cata-lyst supports,sensing,hydrogen storage6due to the remarkable properties including low density,large specific surface area, and accessible porosity and so on.It was reported that porous carbon spheres with three-dimensionally ordered pore structure would benefit the mass transport of reactants and products, which is crucial for an excellent catalyst support resulting in better ORR performance.7This suggests that HCMS could be potential support materials for cathodic catalysts in PEMFCs.8 On the other hand,to improve the durability and the attach-ment of Pt NPs on carbon support materials,their surfaces have usually been modified by various methods,such as harsh chemical or electrochemical oxidations with concentrated strong acid,9surface functionalization by anchoring or grafting organic groups(e.g.,amino)on the carbon support surface10 and doping with foreign atoms11(e.g.,nitrogen).Compared with the detrimental oxidation processes9and the complex and time-consuming functionalization process,nitrogen doping of the carbon support materials has been reported as a more effec-tive route to improve the deposition of metal nanoparticles.11According to previous researches,11,12nitrogen-doped carbon supports not only facilitate the dispersion of Pt NPs but render Pt NPs a higher durability by introducing more binding sites to the carbon surface for anchoring the Pt precursor or Pt NPs. Moreover,some researches showed that nitrogen-doped carbon itself has a certain activity toward ORR.13Thus,nitrogen-doped hollow carbon microspheres(N-HCMS)should be the promising carbon support materials.Herein,N-HCMS were fabricated by pyrolysis of poly(dopa-mine)(PDA)wrapped SiO2microspheres which were synthe-sized by the spontaneous self-polymerization of dopamine onto the surface of silica microspheres and employed as the support material for Pt NPs.The electrocatalytic performance of the as-prepared N-HCMS supported Pt NPs(Pt/N-HCMS)for ORR was investigated by typical electrochemical methods.2Experimental2.1Reagents and materialsDopamine hydrochloride(DA)and SiO2microspheres(di-ameter,ca360nm)were purchased from Alfa Aesar(USA) and used as received.All other reagents were of analytical grade.All solutions used throughout were prepared with ultra pure water obtained from a Millipore system(>18MΩ·cm). 2.2Synthesis of N-HCMSThe synthesis for N-HCMS was composed of three steps as reported by Xiao et al.,14and a typical procedure is detailed as follows.Firstly,100mg SiO2microspheres were washed thor-oughly with50mmol·L-1tris(hydroxymethyl)-aminomethane (TRIS)buffer(pH=8.5)and centrifuged for three times.The re-sulting precipitate was then suspended in TRIS buffer solution (40mL,50mmol·L-1)containing80mg dopamine hydrochlo-ride,followed by vigorous stirring for24h to form polydopa-mine(PDA)wrapped SiO2(PDA/SiO2)microspheres.After centrifugated,washed with TRIS buffer solution and dried in vacuum at60°C overnight,PDA/SiO2microspheres were ob-tained and then carbonized in a nitrogen atmosphere at850°C for2h.Finally,the product,denoted as N-HCMS,was ob-tained via removing the silica core of the carbonized PDA/SiO2 microspheres in2mol·L-1HF+8mol·L-1NH4F aqueous solu-tion at room temperature for2h,followed by successive cen-trifugation(13000r·min-1),washing with water several times, and drying under vacuum.2.3Preparation of Pt/N-HCMSDeposition of Pt NPs on the N-HCMS was achieved via mi-crowave-assisted reduction process in ethylene glycol.15Typi-cally,20mg of N-HCMS was dispersed in25mL ethylene gly-1298ZHANG Xiao-Hua et al .:Well-Dispersed Platinum Nanoparticles Supported on N-HCMS for ORRNo.6col and then 1.33mL of H 2PtCl 6precursor (19.3mmol ·L -1)was added.After adjusting pH value to 8-9with 1.0mol ·L -1KOH aqueous solution,the suspension was ultra-sonicated for 30min,and then heated by microwave irradiation (800W)for 10min at 120°C.The resulting mixture was filtered and washed with ultra pure water and acetone several times to thoroughly remove physically absorbed ethylene glycol,followed by dry-ing in a vacuum oven for 24h,and then the final product,de-noted as Pt/N-HCMS,was obtained.The loading mass of Pt NPs in Pt/N-HCMS nanohybrids was determined by inductive-ly coupled plasma-atom emission spectroscopy (ICP-AES)and it was about 18.58%(mass fraction).2.4Physical characterizationThe morphology and structure of N-HCMS and Pt/N-HCMS were characterized by transmission electron microscopy (TEM,JEM-3010,Japan)and scanning electron microscopy (SEM,JSM-6700F,Japan).X-ray diffraction (XRD)analyses were carried out on a Philips X ʹPert PROSUPER X-ray diffrac-tometer equipped with graphite monochromatized Cu K αradia-tion.ICP-AES measurement was conducted on an Atomscan Advantage spectrometer (Thermo Ash Jarrell Corporation,USA).Nitrogen sorption isotherms and Brunauer-Emmett-Teller (BET)surface areas of the samples were determined by an ASAP 2020M+C automatic micropore and chemisorption ana-lyzer (USA).Nitrogen content of N-HCMS determined by ele-mental analyzer (TCH-600,USA)was about 6.58%(mass frac-tion).2.5Electrochemical measurementsElectrochemical measurements were performed in a typical three-electrode cell with a platinum wire as the counter elec-trode and a Ag/AgCl/KCl (3mol ·L -1)electrode as the refer-ence electrode under the control of Autolab PGSTAT12.All the potentials reported herein were with respect to Ag/AgCl.For preparing the working electrode,3mg of catalyst (Pt/N-HCMS or E-TEK Pt/C (the commercial catalyst,De Nora Elettrodi Co.Ltd.,20%Pt (mass fraction))was firstly suspended in 1mL water with ultrasonication to achieve uniform catalyst ink,and then a definite volume of catalyst ink was transferred to the surface of the glassy carbon (GC)rotatable disk electrode (RDE,ϕ5mm,Pine Instruments)by a micro-syringe.The loading mass of Pt NPs for the Pt/N-HCMS or E-TEK Pt/C cat-alyst was 30μg ·cm -2.After dried in air,the electrode was coat-ed with 5μL of 0.5%(mass fraction)Nafion ethanol solution (Ion Power Inc.,USA).Prior to each electrochemical measure-ment,the electrode was cycled in Ar-saturated 0.5mol ·L -1H 2SO 4solution until a steady-state cyclic voltammogram was reached.RDE tests were conducted at a scan rate of 10mV ·s -1with a rotation speed of 1600r ·min -1(revolution per minute)in O 2-saturated 0.5mol ·L -1H 2SO 4solution.All of the electrochemi-cal experiments were performed at 25°C.3Results and discussionFig.1SEM (A)and TEM (B)images of N-HCMS,and nitrogen adsorption-desorption isotherms (C)andthe pore size (D )distributions (D)of N-HCMS and Pt/N-HCMSThe inset in Fig.1A is the high-magnification SEM image ofN-HCMS.1299Acta Phys.-Chim.Sin.2013Vol.293.1Characterization of N-HCMS and Pt/N-HCMSFig.1shows the SEM and TEM images of N-HCMS.It is noted that the hollow feature of the microspheres with uniform diameter and shell thickness can be clearly observed,and the average diameter and the shell thickness of N-HCMS is about 372and 12nm,respectively.For further understanding the pore structure,N 2adsorption-desorption isotherms of N-HCMS were measured,and the corresponding N 2adsorption-desorp-tion isotherms are shown in Fig.1C.From Fig.1C,a type IV isotherm with an H 1-type hysteresis loop at high relative pres-sure can be observed,which means that the obtained N-HCMS possesses mesoporous structure.The BET surface areas of N-HCMS and Pt/N-HCMS calculated from the results of nitro-gen adsorption are 745and 501m 2·g -1,respectively,obviously higher than that of Vulcan XC-72(232m 2·g -1),16a kind of car-bon materials which has been widely used as catalyst support in fuel pared with that of N-HCMS,the lower BET surface area of Pt/N-HCMS might be attributed to the introduc-tion of Pt nanoparticles to the N-HCMS mesopore structure.8b The pore size distribution (PSD)(Fig.1D)of N-HCMS is al-so calculated from the nitrogen adsorption isotherm using the Barrett-Joyner-Halenda (BJH)model.N-HCMS have a wide pore size distribution in the range of 2-8nm and the highest PSD peak centers at 4.0nm,revealing that N-HCMS consist mostly of mesopores which plays a significant role in mass transfer in ORR.17Based on the hollow structure,high specific surface area,accessible porosity,and N-doping,N-HCMS can be expected as a satisfactory support material for Pt NPs.Figs.2A and 2B show the TEM images of Pt/N-HCMS.From Figs.2A and 2B,well-dispersed Pt NPs were successfully deposited on the surface N-HCMS via microwave-assisted re-duction process.The size distribution was evaluated statistical-ly through measuring the diameter of 200Pt NPs in the select-ed TEM image (Fig.2B),and the corresponding results are shown in Fig.2C.From Fig.2C,the particle size of Pt distrib-utes mainly between 1.3and 6.0nm with an average diameter of ca (4.1±0.4)nm,which is larger than that of E-TEK Pt/C,ca (2.0±0.3)nm.Noteworthy is that no NPs aggregation is obvi-ously observed on the surface of N-HCMS.The structure and composition of the N-HCMS and Pt/N-HCMS were further in-vestigated by XRD (Fig.2D).From Fig.2D,for N-HCMS and Pt/N-HCMS,one broad diffraction peak at 2θof around 25°corresponding to turbostratic carbon (002)lattice plane can be observed,suggesting poor graphitization of N-HCMS under the carbonization temperature of 850°C.18Besides,the diffrac-tion peaks at around 40°,46°,68°,and 82°indexed to Pt (111),(200),(220),and (311)planes,respectively,the typical char-acter of a crystalline face centered cubic (fcc)phase of Pt,can also be observed on Pt/N-HCMS,demonstrating the suc-cessful preparation of the Pt/N-HCMS nanohybrids.The mean Pt particle size of Pt/N-HCMS catalyst,calculated from the XRD pattern using the Debye-Scherrer equation,19is 4.2nm,which is in good agreement with the result observed from the TEM images.Fig.2(A,B)TEM images of Pt/N-HCMS,(C)size distribution of Pt NPs of Pt/N-HCMS nanohybrids,(D)X-ray diffraction patterns ofN-HCMS and Pt/N-HCMSnanohybrids1300ZHANG Xiao-Hua et al .:Well-Dispersed Platinum Nanoparticles Supported on N-HCMS for ORRNo.63.2Electrocatalytic properties of the Pt/N-HCMS catalyst for oxygen reductionThe electrocatalytic properties of the as-fabricated Pt/N-HCMS nanohybrids toward the ORR were evaluated and com-pared with that of the commercial E-TEK Pt/C.Fig.3A shows typical ORR polarization curves of Pt/N-HCMS and E-TEK Pt/C catalysts in oxygen-saturated 0.5mol ·L -1H 2SO 4by using a glassy carbon RDE at 1600r ·min -1.As expected,the Pt/N-HCMS catalyst shows higher catalytic activity toward the ORR compared to the E-TEK Pt/C catalyst.From Fig.3A,the onset and half-wave potentials of ORR on the Pt/N-HCMS catalyst are about 0.736and 0.605V ,respec-tively,and positively shifted by about 38and 30mV in compar-ison with those on the E-TEK Pt/C catalyst.Moreover,the mass activity of the Pt/N-HCMS catalyst,in term of mass spe-cific current density at 0.65V is 32.21A ·g -1,being 1.9times as high as than that on the E-TEK Pt/C catalyst (16.28A ·g -1).These indicate that the electrocatalytic activity of Pt/N-HCMS for ORR is better than that of E-TEK Pt/C.To clarify the mechanism about the higher electrocatalytic activity of Pt/N-HCMS compared with that of E-TEK Pt/C,the specific electrochemical surface area (ESA)of Pt/N-HCMS (or E-TEK Pt/C)was estimated by cyclic voltammetry (CV)based on the charge associated with the hydrogen adsorption and de-sorption processes 20in Ar-saturated 0.5mol ·L -1H 2SO 4solution at a scan rate of 50mV ·s -1,and the corresponding cyclic voltam-mograms are presented in Fig.3B.The ESA values of the Pt/N-HCMS and E-TEK Pt/C catalysts can be calculated as:2ESA=Q H /(0.21×[Pt])where Q H (mC ·cm -2)represents the mean value between the amounts of charge exchanged during the electro-adsorption and desorption of H 2on Pt sites,[Pt]is the Pt loading (mg ·cm -2)on the electrode and 0.21(mC ·cm -2)represents the charge required to oxidize a monolayer of H 2on a smooth Pt.The ESA value (Fig.3C)of Pt/N-HCMS catalyst is about 39.3m 2·g -1and lower than that of the E-TEK Pt/C catalyst (48.9m 2·g -1).The lower ESA of Pt/N-HCMS compared with that of E-TEK Pt/C is reasonable since Pt/N-HCMS have larger Pt size (about 4nm)compared with that of E-TEK Pt/C (about 2nm).However,it is worthy to investigate why the Pt/N-HCMS catalyst with the smaller ESA value exhibits better electrocata-lytic activity towards ORR.From a more basic chemical point of view,the specific sur-face activity,calculated by normalizing the current density to the ESA,can be used to conclude about the intrinsic activity of the catalyst.Therefore,the specific surface activities of the Pt/N-HCMS and E-TEK Pt/C catalysts were calculated and are about 1.025and 0.371A ·m -2,respectively (Fig.3D),indicating that the Pt/N-HCMS catalyst has not only higher mass specific activity but also higher intrinsic activity for the ORR than theFig.3(A)RDE tests toward ORR on the Pt/N-HCMS and E-TEK Pt/C catalysts at 1600r ·min -1in O 2-saturated 0.5mol ·L -1H 2SO 4with a scan rate of 10mV ·s -1;(B)cyclic voltammograms of the Pt/N-HCMS and E-TEK Pt/C catalysts in Ar-saturated 0.5mol ·L -1H 2SO 4at 50mV ·s -1;(C)ESA values of the Pt/N-HCMS and E-TEK Pt/C catalysts;(D)mass activity and specific activity of the Pt/N-HCMS and E-TEKPt/C catalysts at 0.65V1301Acta Phys.-Chim.Sin.2013Vol.29E-TEK Pt/C catalyst.It is well known that the intrinsic activity of catalyst mainly depends on its nature such as property and structure of material.These suggest that the N-HCMS can im-prove the catalytic activity of Pt due to the following probable reasons:(1)the existence of nitrogen atoms in N-HCMS chang-es the chemical composition of the HCMS and favors to in-crease specific active sites at the metal-support boundary,16thus benefiting the effective attachment and uniform dispersion of Pt NPs onto the surface of N-HCMS;(2)the nitrogen acts as a electron donator and improves the electrical conductivity of the N-HCMS,resulting in a faster electron transfer process of ORR;22(3)it is well known that ORR in fuel cells involves O 2-ions,electrons and O 2molecules,in which O 2molecules react with electrons at the cathode to form O 2-ions which are trans-ported from the reaction site by diffusion.For an ideal catalyst toward ORR in fuel cells,the structure with high electrical con-ductivity,ion conductivity,and gas permeability is necessary.23The mesoporous and hollow structure of N-HCMS provides the ideal channels of electron and mass transport,thus facilitat-ing the process of oxygen reduction.In addition,nitrogen-doped carbon itself has a certain activity toward ORR.13a In or-der to further clarify the effect of nitrogen doping on the disper-sion of Pt NPs and the electrocatalytic properties of the cata-lysts,the un-doped HCMS supported Pt NPs (Pt/HCMS)were prepared,the more detailed procedure for the preparation of Pt/HCMS,and the related structure characterization and electro-catalytic properties were provided in Supporting Information.As showed in Fig.S1A,Pt NPs are obviously aggregated on the surface of paring Pt/HCMS (0.624V ,2.88mA ·cm -2),Pt/N-HCMS (0.736V ,4.81mA ·cm -2)catalyst exhibits more positive onset potential and higher steady-state diffusion current density for oxygen reduction (Fig.S2).These further confirm that nitrogen doping is helpful for the uniform disper-sion of Pt NPs onto the surface of the carbon spheres and the enhancement of the electrocatalytic activity of the Pt catalysts.3.3Durability of the Pt/N-HCMS catalystThe durability of the electrocatalyst is very important from a practical viewpoint.The long term electrochemical stability of the catalyst was evaluated by accelerated degradation test (ADT).The ADT was performed by CV cycling between 0.4and 0.8V in O 2-saturated 0.5mol ·L -1H 2SO 4solution with a scan rate of 100mV ·s -1.Before and after ADT,the ESA values of the Pt/N-HCMS catalyst were evaluated by the CV tests in Ar-saturated 0.5mol ·L -1H 2SO 4solutions with a scan rate of 50mV ·s -1and the related RDE tests toward ORR were carried out at 1600r ·min -1in O 2-saturated 0.5mol ·L -1H 2SO 4with a scan rate of 10mV ·s -1.For comparison,the commercial E-TEK Pt/C catalyst was al-so studied under the same conditions.Figs.4A and 4B show the CV curves of the Pt/N-HCMS and E-TEK Pt/C catalysts before and after 2000CV cycles.The loss of the ESA with the number of CV cycle is plotted in Fig.4C.As shown in Fig.4C,the ESA value of the Pt/N-HCMS catalyst after 2000CV cycles only decreases about 18%,while E-TEK Pt/C loses 79%of the initial ESA.On the other hand,a larger decrease of 116mV (Fig.4E)in the half-wave potential can be observed for the E-TEK Pt/C catalyst after 2000CV cy-cles compared with that of the Pt/N-HCMS catalyst (14mV ,Fig.4D).Fig.5(A -D)shows the TEM images of the Pt/N-HCMS and E-TEK Pt/C catalysts before and after CV cycling.For the E-TEK Pt/C catalyst (Figs.5B and 5D),substantial growth of Pt NPs and a decrease of the distribution density of Pt NPs on the carbon supports can be observed after the durability test.Fig.4CV curves for the Pt/N-HCMS (A)and E-TEK Pt/C (B)catalysts before and after ADT;loss of ESA of Pt/N-HCMS and E-TEK Pt/Cwith the number of CV cycles (C);RDE tests of Pt/N-HCMS (D)and E-TEK Pt/C (E)before and afterADT1302ZHANG Xiao-Hua et al .:Well-Dispersed Platinum Nanoparticles Supported on N-HCMS for ORRNo.6The average size of Pt NPs of E-TEK Pt/C (Fig.5F)is ca (5.1±1.3)nm,increases about 155.0%compared with that before CV tests.This implies that the loss of ESA for the E-TEK Pt/C was ascribed to the Ostwald ripening,aggregation,and falling-off of the Pt NPs on the carbon support.24By contrast,in addi-tion to slight aggregation,there were no obvious morphologi-cal changes (see Figs.5A and 5C)for the Pt/N-HCMS catalyst after CV cycling,and the average size of Pt NPs of Pt/N-HCMS (see Fig.5E)is ca (5.0±1.3)nm,only increases about 21.9%than that before CV tests.The above ESA data,TEM and size distribution results indicate that Pt/N-HCMS is much more sta-ble than the commercial E-TEK Pt/C catalyst.On the other hand,a larger decrease of the half-wave potential and ESA (32.5mV and 23%,respectively,Fig.S3)can also be observed for the Pt/HCMS catalysts after 2000CV cycles compared with that of the Pt/N-HCMS catalyst.These imply that nitro-gen doping is beneficial to the improvement of the stability of the Pt/N-HCMS catalyst.11a,12a,12c,12d,254ConclusionsN-HCMS were synthesized by carbonization of poly(dopa-mine)and then employed as the support for Pt NPs.Due to the high specific surface area and homogeneous N-doping sites of N-HCMS,Pt NPs are highly dispersed on the surface of paring the E-TEK Pt/C catalyst,the Pt/N-HCMS cata-lyst exhibits significantly enhanced electrocatalytic activity to-ward ORR and improved long-term electrochemical stability due to the excellent support effect of N-HCMS for Pt NPs.The N-HCMS should be a promising catalyst support for noble metal NPs in fuel cells.Supporting Information:available free of charge via the in-ternet at .References(1)Borup,R.;Meyers,J.;Pivovar,B.;Kim,Y .S.;Mukundan,R.;Garland,N.;Myers,D.;Wilson,M.;Garzon,F.;Wood,D.;Zelenay,P.;More,K.;Stroh,K.;Zawodzinski,T.;Boncella,J.;McGrath,J.E.;Inaba,M.;Miyatake,K.;Hori,M.;Ota,K.;Ogumi,Z.;Miyata,S.;Nishikata,A.;Siroma,Z.;Uchimoto,Y .;Yasuda,K.;Kimijima,K.I.;Iwashita,N.Chem.Rev.2007,107(10),3904.doi:10.1021/cr050182l (2)(a)Lim,B.;Jiang,M.;Camargo,P.H.C.;Cho,E.C.;Tao,J.;Lu,X.;Zhu,Y .;Xia,Y .Science 2009,324(5932),1302.doi:10.1126/science.1170377(b)Bing,Y .;Liu,H.;Zhang,L.;Ghosh,D.;Zhang,J.Chem.Soc.Rev.2010,39(6),2184.(3)Wang,C.;Daimon,H.;Onodera,T.;Koda,T.;Sun,S.Angew.Chem.Int.Edit.2008,47(19),3588.(4)Yu,X.;Ye,S.J.Power Sources 2007,172(1),145.doi:10.1016/j.jpowsour.2007.07.048(5)Thompson,S.D.;Jordan,L.R.;Forsyth,M.Electrochim.Acta2001,46(10-11),1657.(6)(a)Wen,Z.;Wang,Q.;Zhang,Q.;Li,mun.2007,9(8),1867.doi:10.1016/j.elecom.2007.04.016(b)Sun,X.;Li,Y .Angew.Chem.Int.Edit.2004,43(29),3827.(c)Su,F.;Zhao,X.S.;Wang,Y .;Wang,L.;Lee,J.Y .J.Mater.Chem.2006,16(45),4413.(d)Huang,H.;Remsen,E.E.;Kowalewski,T.;Wooley,K.L.J.Am.Chem.Soc.1999,121(15),3805.Fig.5TEM images of Pt/N-HCMS (A,C)and E-TEK Pt/C (B,D)before (A,B)and after (C,D)2000CV cycle tests;size distribution of PtNPs of Pt/N-HCMS (E)and E-TEK Pt/C (F)after 2000CV cycling testsInset in figure F:size distribution of Pt NPs of E-TEK Pt/C before 2000CV cyclingtests1303Acta Phys.-Chim.Sin.2013Vol.29(e)Han,S.;Yun,Y.;Park,K.W.;Sung,Y.E.;Hyeon,T.Adv.Mater.2003,15(22),1922.(f)Gill,I.;Ballesteros,A.J.Am.Chem.Soc.1998,120(34),8587.(g)Du,H.;Li,B.;Kang,F.;Fu,R.;Zeng,Y.Carbon2007,45(2),429.(7)Bang,J.H.Electrochim.Acta2011,56(24),8674.doi:10.1016/j.electacta.2011.07.066(8)(a)Fang,B.;Kim,J.H.;Lee,C.;Yu,J.S.J.Phys.Chem.C2007,112(2),639.(b)Fıçıcılar,B.;Bayrakçeken,A.;Eroǧlu,İ.Int.J.Hydrog.Energy2010,35(18),9924.(9)(a)Jun,S.;Choi,M.;Ryu,S.;Lee,H.Y.;Ryoo,R.OrderedMesoporous Carbon Molecular Sieves with FunctionalizedSurfaces.In Studies in Surface Science and Catalysis;Sang-Eon Park,R.R.W.S.A.C.W.L.,Jong-San,C.,Eds.;Elsevier:2003;V ol.146,p37.(b)Tang,H.;Chen,J.H.;Huang,Z.P.;Wang,D.Z.;Ren,Z.F.;Nie,L.H.;Kuang,Y.F.;Yao,S.Z.Carbon2004,42(1),191.(10)(a)Besson,E.;Mehdi,A.;Reye,C.;Corriu,R.J.P.J.Mater.Chem.2009,19(27),4746.doi:10.1039/b902568e(b)Yang,C.M.;Liu,P.H.;Ho,Y.F.;Chiu,C.Y.;Chao,K.J.Chem.Mater.2002,15(1),275.(11)(a)Chen,Y.;Wang,J.;Liu,H.;Li,R.;Sun,X.;Ye,S.;Knights,mun.2009,11(10),2071.doi:10.1016/j.elecom.2009.09.008(b)Saha,M.S.;Li,R.;Sun,X.;Ye,mun.2009,11(2),438.(12)(a)Higgins,D.C.;Meza,D.;Chen,Z.J.Phys.Chem.C2010,114(50),21982.doi:10.1021/jp106814j(b)Chen,Y.;Wang,J.;Liu,H.;Banis,M.N.;Li,R.;Sun,X.;Sham,T.K.;Ye,S.;Knights,S.J.Phys.Chem.C2011,115(9),3769.(c)Li,X.;Park,S.;Popov,B.N.J.Power Sources2010,195(2),445.(d)Liu,Z.;Su,F.;Zhang,X.;Tay,S.W.ACS Applied Materials&Interfaces2011,3(10),3824.(13)(a)Lefèvre,M.;Proietti,E.;Jaouen,F.;Dodelet,J.P.Science2009,324(5923),71.doi:10.1126/science.1170051(b)Shao,Y.;Sui,J.;Yin,G.;Gao,Y.Applied Catalysis B:Environmental2008,79(1),89.(c)Wang,X.;Dai,S.Angew.Chem.Int.Edit.2010,49(37),6664.(d)Ma,G.;Jia,R.;Zhao,J.;Wang,Z.;Song,C.;Jia,S.;Zhu,Z.J.Phys.Chem.C2011,115(50),25148.(e)Shanmugam,S.;Osaka,mun.2011,47(15),4463.(f)Yang,W.;Fellinger,T.P.;Antonietti,M.J.Am.Chem.Soc.2010,133(2),206.(g)Bezerra,C.W.B.;Zhang,L.;Lee,K.;Liu,H.;Marques,A.L.B.;Marques,E.P.;Wang,H.;Zhang,J.Electrochim.Acta2008,53(15),4937.(14)Xiao,C.;Chu,X.;Yang,Y.;Li,X.;Zhang,X.;Chen,J.Biosens.Bioelectron.2011,26(6),2934.doi:10.1016/j.bios.2010.11.041 (15)Wu,B.;Hu,D.;Kuang,Y.;Liu,B.;Zhang,X.;Chen,J.Angew.Chem.Int.Edit.2009,48(26),4751.doi:10.1002/anie.v48:26 (16)Maiyalagan,T.;Viswanathan,B.;Varadaraju,U.V.mun.2005,7(9),905.doi:10.1016/j.elecom.2005.07.007(17)(a)Su,F.;Poh,C.K.;Tian,Z.;Xu,G.;Koh,G.;Wang,Z.;Liu,Z.;Lin,J.Energ.Fuel2010,24(7),3727.doi:10.1021/ef901275q(b)Stein,A.;Wang,Z.;Fierke,M.A.Adv.Mater.2009,21(3),265.(18)Kyotani,T.;Nagai,T.;Inoue,S.;Tomita,A.Chem.Mater.1997,9(2),609.doi:10.1021/cm960430h(19)Ramgir,N.S.;Hwang,Y.K.;Mulla,I.S.;Chang,J.S.SolidState Sci.2006,8(3-4),359.(20)Pozio,A.;De Francesco,M.;Cemmi,A.;Cardellini,F.;Giorgi,L.J.Power Sources2002,105(1),13.doi:10.1016/S0378-7753(01)00921-1(21)Xu,Y.;Lin,X.Electrochim.Acta2007,52(16),5140.doi:10.1016/j.electacta.2007.02.037(22)Kong,J.;Dai,H.J.Phys.Chem.B2001,105(15),2890.doi:10.1021/jp0101312(23)Hayashi,A.;Notsu,H.;Kimijima,K.I.;Miyamoto,J.;Yagi,I.Electrochim.Acta2008,53(21),6117.doi:10.1016/j.electacta.2008.01.110(24)Liu,L.;Huang,Z.;Wang,D.;Scholz,R.;Pippel,E.Nanotechnology2011,22(10),105604.doi:10.1088/0957-4484/22/10/105604(25)Li,Y.H.;Hung,T.H.;Chen,C.W.Carbon2009,47(3),850.doi:10.1016/j.carbon.2008.11.0481304。