[Article]
https://www.doczj.com/doc/c37518487.html,
物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin .2014,30(2),318-324
February
Received:October 14,2013;Revised:December 11,2013;Published on Web:December 12,2013.?
Corresponding author.Email:pangs@https://www.doczj.com/doc/c37518487.html,;Tel:+86-755-26957243.
The project was supported by the National Natural Science Foundation of China (91223202),International Science &Technology Cooperation Program of China (2011DFA73410),Tsinghua University Initiative Scientific Research Program,China (20101081907),and National Key Basic Research Program of China (973)(2011CB013102).
国家自然科学基金(91223202),国家国际科技合作专项项目(2011DFA73410),清华大学自主科研计划(20101081907)及国家重点基础研究发展规划项目(973)(2011CB013102)资助
?Editorial office of Acta Physico -Chimica Sinica
doi:10.3866/PKU.WHXB201312121
Fe-N/C-TsOH 催化剂应用碱性介质催化氧还原的电催化活性
徐
莉1,2
潘国顺1,2,*
梁晓璐1,2
罗桂海1,2邹春莉1,2罗海梅1,2
(1清华大学摩擦学国家重点实验室,北京100084;
2
深圳清华大学研究院深圳市微纳制造重点实验室,广东深圳518057)
摘要:
通过溶剂分散热处理方法制备了一种吡咯和对甲苯磺酸(TsOH)共同修饰的碳载非贵金属复合催化剂
(Fe-N/C-TsOH),并采用扫描电子显微镜(SEM)、X 射线衍射(XRD)和X 射线光电子能谱(XPS)对催化剂的形貌和组成成分进行表征.借助循环伏安法(CV)和旋转圆盘技术研究了TsOH 对催化剂在0.1mol ?L -1KOH 介质中催化氧还原性能的影响.结果表明:TsOH 的存在对催化剂催化氧还原反应(ORR)的活性影响很大.以其制备的气体扩散电极在碱性电解质溶液中催化氧还原过程时转移的电子数为3.899,远比不含TsOH 修饰的催化剂催化氧还原的电子数(3.098)高.此外,研究发现600°C 热处理过的Fe-N/C-TsOH 催化剂表现出最佳的氧还原催化性能.相比未经热处理过的Fe-N/C-TsOH 催化剂,起峰电位和-1.5mA ?cm -2电流密度对应的电压分别向正方向移动30和170mV.XPS 研究结果表明吡咯氮是催化剂主要活性中心,提供氧还原活性位,而TsOH 加入形成的C ―S n ―C 和―SO n ―有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.关键词:
非贵金属催化剂;双杂化;热处理;碱性燃料电池;氧还原反应
中图分类号:
O646
Electrocatalytic Activity of Fe-N/C-TsOH Catalyst for the Oxygen
Reduction Reaction in Alkaline Media
XU Li 1,2
PAN Guo-Shun 1,2,*LIANG Xiao-Lu 1,2
LUO Gui-Hai 1,2
ZOU Chun-Li 1,2LUO Hai-Mei 1,2
(1The State Key Laboratory of Tribology,Tsinghua University,Beijing 100084,P .R.China ;2Shenzhen Key Laboratory of Micro/
nano Manufacturing,Research Institute of Tsinghua University in Shenzhen,Shenzhen 518057,Guangdong Province,P .R.China )
Abstract:Pyrolyzed carbon supported ferrum polypyrrole (Fe-N/C)catalysts were synthesized with and without the dopant p -toluenesulfonic acid (TsOH)through a solvent-grinding method followed by heat-treatment at the desire temperature.Both the catalysts were characterized using electrochemical techniques,such as cyclic voltammetry (CV),as well as the rotating disk electrode (RDE)technique.It was found that the catalysts doped with TsOH showed significantly better oxygen reduction reaction (ORR)activity than the undoped catalysts.The average electron transfer numbers for the catalyzed ORR were 3.899and 3.098for the TsOH-doped and undoped catalysts,respectively.Thermal treatment was found to be a necessary step for catalyst activity improvement.The catalyst pyrolyzed at 600°C showed the best ORR activity:the onset potential and the potential at the current density of -1.5mA ?cm -2for the TsOH-doped catalyst were 30and 170mV more positive than those for the un-pyrolyzed TsOH-doped catalyst,respectively.To clarify the effects of TsOH doping and pyrolyzation,scanning electron microscopy (SEM),X-ray diffraction (XRD),and X-ray photoelectron spectroscopy (XPS)were used to analyze the morphology,
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XU Li et al.:Electrocatalytic Activity of Fe-N/C-TsOH Catalyst for the Oxygen Reduction Reaction in Alkaline Media No.2
structure,and composition of the catalysts.The XPS results suggest that the pyrrolic-N groups are the most active sites and sulfur species are structurally bound to carbon in the form of C―S n―C and oxidized―SO n―bonds,which is an additional beneficial factor for the ORR.
Key Words:Non-noble metal catalyst;Dual-dopant;Heat-treatment;Alkaline fuel cell;
Oxygen reduction reaction
1Introduction
In response to increasing awareness of environmental pollu-tion and limiting energy source,great effort has been made worldwide to generate power in more efficient and environ-mental friendly ways.Fuel cells have attracted significant at-tention as a promising technology due to their advantages such as high energy density,high power density,and high energy conversion efficiency,as well as their low or zero emission.1 However,there are two fundamental catalytic challenges re-mained at our current technology,including prohibitive cost and inadequate durability,hampered the commercialization of fuel cells.With respect to the high cost,Pt-based catalysts which have been regarded as the most electrocatalyst for oxy-gen reduction reaction(ORR)contributes over50%of the total cost of a fuel cell stack.2One solution to overcome this predica-ment is to reduce the Pt content by a factor of ten by replacing the Pt-based catalysts with non-precious metal catalysts at the oxygen-reduction cathode.Fe-and Co-based electrocatalysts (M-N x/C)for this reason have been developed for more than50 years,but they were insufficiently active for the high efficien-cy and power density needed for applications such as station-ary,portable,and automobile power supplies.3,4However,sev-eral breakthroughs occurred have improved the activity and du-rability of those kinds of catalysts,which can now be treated as potential competitors to Pt-based catalysts.
In addition,it has been recognized that the nitrogen sources in the catalyst precursors during the M-N x/C synthesis play a crucial role in ameliorating ORR activity as well as stability. And this is the reason why several different types of nitrogen-containing macrocycles,inorganic salts,and organometallic compounds have been employed as the precursors to form metal-nitrogen complexes.5-11
Polypyrrole(PPy),a conducting polymer with many pyrrole-type N atoms,altering surface,and easy preparation and dop-ing,has been widely used for the synthesis of M-N x/C since it was first investigated by Yuasa et al.12in2005.Yuasa et al. found that Co-PPy/C ORR activity enhanced after being pyro-lyzed for the cobalt site forming four coordinate bonds with the nitrogen of the PPy rings(Co-N4).Bashyam and Zelenary3 deposited PPy on carbon black to form a catalyst support(PPy/ C)via an oxidative polymerization process using hydrogen per-oxide.After impregnating cobalt ions,a carbon-supported co-balt catalyst(Co-PPy/C)was generated.Research showed that sodium borohydride as reductive agent could improve the cata-lyst activity and stability and Co-N2may be active site.
Furthermore,thermal-treatment has been recognized as a cru-cial role and sometimes necessary step to further improve the activity and stability.Although the heat-treatment effect on cat-alysts has been well documented,the mechanisms of the cata-lyst reaction during the heat-treatment process and the result-ing improvement in activity are complicated and not fully un-derstood.Reviewing many papers,thermal activation has sig-nificant impact on the metal particle size and size distribution, particle surface morphology,and metal dispersion on the sup-port for such catalyst.Other benefits of heat treatment are to re-move any undesirable impurities and allow a uniform disper-sion and stable distribution of the transition metal on the sup-port,and,therefore,to improve the electrocatalytic activity.13 In addition,when the catalysts are pyrolyzed at a desired high temperature in a flowing inert atmosphere(nitrogen or argon), M-N precursor is partially or completely decomposed,result-ing in a catalyst with much better catalytic activity and stabili-ty than a untreated catalyst.14
To further improve the activity,dual-doped carbons with two different heteroatoms become one promising option for ORR by taking advantage of different heteroatoms in conjugat-ed carbon backbone that can create new non-electron-neutral sites.In particular,the sulfur(or sulfo group),which has a close electronegativity to carbon,has been employed as a dual-dopant in the preparation of M-N x catalysts.It was thought that the sulfur group doped to the M-N x/C might be helpful for en-trapping M ions in an environment rich in pyrrole-type nitro-gen or pyridine-type nitrogen.For instance,N/S co-doped Vul-can XC-72R has been demonstrated to show superior ORR per-formance with excellent activity9and durability.14
Based on the above conception,p-toluenesulfonic acid(TsOH) and polypyrrole were used as dual-dopant(S and N)to synthe-size a novel non-precious metal catalyst based on carbon-sup-ported ferrum,polypyrrole,and TsOH complex(Fe-N/C-TsOH).In particular,TsOH,an organic compound,is known as tosyl group and not only was used as the S precursor,but also used as an“organic-soluble”acid catalyst to promote the oxi-dation of pyrrole.And a comparative study was carried out through the systematic analyses of Fe-N catalysts prepared without and with TsOH dopant by cyclic voltammeters(CVs), rotating disk electrode technique(RDE)in oxygen-saturated al-kaline solutions,and scanning electron microscope(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy (XPS)are used to characterize these catalysts in terms of their structures and compositions.
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2Experimental
2.1Preparation of carbon black-supported Fe-N-S
catalyst
For preparation of carbon black supported Fe-N-S catalyst(Fe-
N/C-TsOH),120mg carbon black(Vulcan XC-72R with a BET
surface area of235m2?g-1,purchased from Cabot)dispersed in 10mL methanol(analytically pure)and then added50mg pyr-
role(chemically pure),followed by10min of ultra-sonication.
0.25mL30%H2O2and50mg TsOH(analytically pure,pur-
chased from Guoyao)were added into this ultrasonication sus-
pension while milling in a mortar for some time to obtain a slur-
ry.10mL methanol with149mg FeSO4?7H2O(analytically
pure)was added into the mortar while followed by constant
grinding for another45min,which was then dried in a vacuum
at60°C for1h to obtain a powder.This powder was further pro-
cessed by thermal treatment under N2atmosphere at200,400,
600,and700°C,respectively,for2h to optimize the heat-treat-
ment temperature with respect to ORR electrolytic activity,form-
ing the final carbon-supported Fe-N-S catalyst.To elucidate the
effect of TsOH alone,a baseline sample of carbon loaded with
TsOH-free Fe-N was also prepared under the same conditions de-
picted above,and is named as Fe-N/C-None in this paper.
2.2Electrochemical measurements
Electrochemical measurements were conducted using a rotat-
ing glassy carbon disk electrode(glassy carbon electrode with
a geometric surface area of0.19625cm2,purchased from Gam-
ry Instruments).According to the electrode preparation method
described by Qiao et al.,1410μL of catalyst ink,which consists
of2.0mg catalyst per mL,was pipetted onto the glassy carbon
(GC)disk electrode.The loading of catalysts was101μg?cm-2.
A saturated calomel electrode(SCE)and Pt wire were used as
the reference and counter electrodes,respectively.All mea-
sured potentials were converted to the standard hydrogen elec-
trode(SHE).
A0.1mol?L-1KOH aqueous solution was used as the elec-
trolyte.For cyclic votammograms(CVs),the electrode was
scanned at a scan rate of50mV?s-1in the potential range be-
tween-0.80and0.30V to measure the surface behavior of the
catalyst in N2-saturated KOH solution,and the ORR activity of
the catalyst in O2-saturated KOH solutions,respectively.For
more quantitative measurements of ORR activity,linear sweep
voltammetry(LSV)was conducted on the catalyst-coated RDE
in the potential range between-0.76and0.15V in O2-saturat-
ed KOH solution at various rotation rates from300to2100r?
min-1.All measured potentials(vs SCE)in this work were con-
verted to the standard hydrogen electrode(SHE),as shown in
the relevant text and figures.
2.3Material characterization
The structure and phase analyses of the catalyst samples
were performed using X-ray diffraction(XRD)with Cu Kαradi-
ation(λ=0.15406nm)and operating at40kV and40mA.The
morphology and particle size of the catalyst samples were stud-
ied using a scanning electron microscope with a Bruker TES-
CAN.Surface characterization of the catalyst samples was con-ducted by X-ray photoelectron spectroscopy on a PHI Quantera Scanning X-ray Microprobe TM5300system(ULVAC-PHI. INC)with Al K X-ray anode source(hv=1486.6eV)at300W and15.0kV.
3Results and discussion
3.1Electrochemical activity of Fe-N/C-TsOH
catalysts towards ORR
CVs of the catalysts pyrolized at600°C prepared without and with TsOH were measured in O2-saturated0.1mol?L-1 KOH solutions with a scan rate of50mV?s-1and the results are presented in Fig.1.In this figure′s legends,“600H”indicat-ed the sample pyrolyzed at600°C.There are obvious redox peaks appeared for two catalysts with a characteristic reduction peak associated with the ORR suggesting that Fe-N/C catalyst has ORR activity regardless of whether they are decorated with TsOH or not.However,more excellent positive peak potential value and higher peak current density were obtained for Fe-N/ C-TsOH-600H catalyst than those for Fe-N/C-None-600H cata-lyst,indicting a better ORR activity after TsOH-doping.That is to say,the addition of TsOH leads to a considerable activity en-hancement of the catalysts relative to the TsOH-free catalyst, which makes us resolutely believe that it is the TsOH or sulfur that plays an important role in enhancing the electrocatalytic performance of carbon materials for the ORR.Yang et al.15con-firmed that the dopant would break the electroneutrality of car-bon materials because the different electroneutrality between carbon and dopant would create favorable positive charged sites for the side-on O2surface adsorption.Pyrolysis of the cata-lyst in the presence of sulfur could lead to amorphous carbon, resulting in an increased catalyst porosity and in turn enhanced catalyst performance.16Besides,larger capacitance current over the potential range for Fe-N/C-TsOH-600H indicated a larger catalyst surface area.
To further clarify the effect of thermal treatment on the ORR activity,the polarization curves were measured using RDE technique with the electrode rotation rate of1500r?min-1in O2-saturated0.1mol?L-1KOH solution for catalysts pyrolyzed from200to700°C,with the unpyrolyzed catalyst sample(Fe-
Fig.1CVs of catalysts doped with and without TsOH in
O2-saturated0.1mol?L-1KOH solution
scan rate:50mV?s-1;catalyst loading:101μg?cm-
2
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XU Li et al .:Electrocatalytic Activity of Fe-N/C-TsOH Catalyst for the Oxygen Reduction Reaction in Alkaline Media
No.2N/C-TsOH-RT)(“RT ”means untreated or unpyrolyzed cata-lyst)for comparison.And the results are given in Fig.2.The py-rolyzed catalysts show better activities than the unpyrolyzed catalyst.There is general agreement in the literature that a heat-treatment step has beneficial effects on the activity.11,13,14,17And the optimal treating temperature is 600°C.The ORR onset po-tential (E onset )and the potential at the current density of -1.5mA ?cm -2for Fe-N/C-TsOH-600H are 30and 170mV ,respec-tively,more positive than Fe-N/C-TsOH-RT.In addition,the diffusion-limiting current for the Fe-N/C-TsOH-600H is also slightly higher than the rest catalysts and shows well-defined plateaus which means that the ORR kinetics catalyzed by Fe-N/C-TsOH-600H is fast enough to exhaust the O 2concentration at the electrode surface.When the thermal temperature is be-low 600°C,with increasing heat-treatment temperature,more Fe-N x active sites could be produced.However,when tempera-ture is higher than 600°C,such as 700°C,not only the struc-ture of the material was collapsed under exceedingly high tem-perature,which results in the material morphology obviously changed,but also the undesired formation of secondary species can be increased,which could lead to a reduced concentration of Fe-N x moieties on the catalyst surface,as shown in the fol-lowing SEM images and XRD patterns.
For a more quantitative evaluation of the ORR catalytic activi-ty of the catalysts developed in our work,RDE voltammetry measurements were also carried out at different electrode rota-tion rates (ω)from 300to 2100r ?min -1,which was demonstrat-ed in Fig.3.The parameters obtained about the two catalysts are listed in Table 1,The difference in diffusion-limiting currents be-tween Fe-N/C-TsOH-600H and Fe-N/C-None-600H may sug-gest that the ORR mechanisms catalyzed by these catalysts are different,particularly in terms of the overall electron transfer number.The ORR catalyzed by pyrolyzed Fe-N/C-TsOH may have more electron numbers (or fewer two-electron processes for peroxide production)than that of the pyrolyzed Fe-N/C-None.The overall electron transfer number (n )during the ORR can be evaluated from the Koutecky-Levich equation.1The per-oxide production yield (y ,%)is calculated from the ring-disk
measurements according to the following equation:18,19
1/j =1/j k +1/j d =1/j k +1/B ω1/2(1)j d =0.2nFC O D O 2/3ν-1/6ω1/2=B ω1/2(2)y (H 2O 2)=50×(4-n )×100%(3)where,j is the current density at specific potential,such as -0.6V ,-0.5V ,etc,j d is the disk ORR current density,j k is the kinetic current density,n is the overall number of electrons transferred per molecule of O 2reduced,F is Faraday ′s constant (F =96485C ?mol -1),C O is the concentration of oxygen dissolved (1.1×10-6mol ?cm -3),D O is the diffusion coefficient of O 2in the bulk solution (1.9×10-5cm 2?s -1),and νis the kinetic viscosity of the solution (1.0×10-2cm 2?s -1).The Koutecky-Levich plots are shown in Fig.4.Based on those plots,we can see that:the average n values were determined to be 3.098for Fe-N/C-None-600H,while 3.899for Fe-N/C-TsOH-600H,which is very close to 4,suggesting that the catalysts doped with TsOH have a higher overall ORR electron number than the catalysts without TsOH,indicating a very difference in the mechanisms catalyzed by these two catalysts.Accordingly,the
percentage
Fig.2Polarization curves for Fe-N/C-TsOH catalysts pyrolyzed at different heat-treatment temperatures
measured in O 2-saturated 0.1mol ?L -1KOH solution at a scan rate of
5mV ?s -1;catalyst loading:101μg ?cm -
2
Fig.3
Polarization curves for ORR on Fe-N/C-TsOH-600H and Fe-N/C-None-600H catalysts in O 2-saturated 0.1mol ?L -1KOH electrolytes at various rotation rates
scan rate:5mV ?s -1
Table 1Comparison of electrochemical data for Fe-N/C-TsOH-600H and Fe-N/C-None-600H catalysts
Catalyst Fe-N/C-None-600H Fe-N/C-TsOH-600H
E onset /V 0.0320.050
I d /(mA ?cm -2)-2.93-4.88
V 1/2/V -0.120-0.104
n 3.0983.899
V 1/2:half-wave potential measured at 1500r ?min -1
;I d :limiting current density measured at -0.75V (vs SHE)
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V ol.30
of H 2O 2produced in the potential range for Fe-N/C-TsOH-600H was less than 15%,while 50%for Fe-N/C-None-600H.In other words,the ORR catalyzed by Fe-N/C-TsOH-600H is a 4-electron transfer process from O 2to H 2O,whereas Fe-N/C-None-600H catalysts generally tend to catalyze the ORR through a (2+2)-electron pathway,producing H 2O 2,which is capable of oxidizing and splitting active sites.
3.2Morphology and structure of the prepared
catalysts
The morphologies of the samples were examined by SEM.As displayed in Fig.5,we can see that the temperature of ther-mal treatment has a direct influence on the morphology and crystal structure of the catalysts.In our study,the catalyst with-out thermal treatment shows some perfect carbon spheres with a smooth surface and a narrow diameter range from 40to 200nm (Fig.5(a)).After being heat-treated at 600°C,the shape of the materials looks like deformed spheres and the aggregate size decreases.What ?s more,there are many small pores on the surfaces of the particles,which help to increase BET surface ar-ea of the materials (Fig.5(b)).For the catalyst sample pyro-lyzed at 700°C,the material morphology has obviously changed,not only the diameter of the sample increased,but also the pores on the surface of the particle decreased (Fig.5(c)).It con-firmed that the structure of the material was collapsed under ex-ceedingly high temperature.
In order to make clear of pyrolysis effect on the ORR activi-ty,Fe-N/C-TsOH-RT,Fe-N/C-TsOH-600H,and Fe-N/C-TsOH-700H samples were chosen for further XRD measurements.The representative diffractograms are shown in Fig.6.A large broad peak located at about 2θ=25°in all the XRD patterns is assigned to the (002)carbon planes of the carbon support with a remarkable disordered structure.From Fig.6,it can be seen that Fe-N/C-TsOH-RT shows some quite strong diffraction peaks due to the crystalline nature of FeSO 4?7H 2O.However,those peaks disappeared after heat treatment.Instead,some ad-ditional diffraction signals were formed at 600and 700°C,which can be due to the generation of metallic iron (α-Fe),iron carbide (Fe 3C),and iron oxide like magnetite (Fe 3O 4)as well as FeS.These results indicate that the structure of the Fe(II)-PPy precursor complex may have decomposed during the heat-treat-ment process.And those species could be a kind of ORR active sites with much less activity than that expected for Fe-N x sites.It is noted that the diffraction signals for Fe-N/C-TsOH-700H are much stronger and sharper than those for Fe-N/C-TsOH-600H.Due to the formation of these less ORR activity species,the quantity of ORR active Fe-N x active sites would be re-duced,resulting in a less ORR activity of the Fe-N/C-TsOH-700H.20
The chemical nature of Fe-N/C-TsOH was further investigat-ed by XPS analysis.The N 1s and S 2p core levels of the cata-lyst material were recorded for both the unpyrolyzed and
pyro-
Fig.4Overall electron transfer number (n )and the amount of peroxide produced during the ORR on the disk electrode and calculated by Eq.(3)for (a)Fe-N/C-TsOH-600H and (b)Fe-N/C-None-600H catalysts in O 2-saturated 0.1mol ?L -1
KOH at the potentials between -0.6and -0.2
V
Fig.5SEM images of Fe-N/C-TsOH (a)without thermal treatment,(b)pyrolyzed at 600°C,and (c)pyrolized at 700
°C
Fig.6
XRD patterns of non-pyrolyzed and pyrolyzed Fe-N/C-TsOH catalysts at 600and 700°C
(a)Fe 3O 4(022);(b)Fe 3O 4(113);(c)Fe(011),Fe 3C(013);
(d)Fe 3O 4(115),(e)Fe 3O 4(044)
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XU Li et al.:Electrocatalytic Activity of Fe-N/C-TsOH Catalyst for the Oxygen Reduction Reaction in Alkaline Media No.2
lyzed Fe-N/C-TsOH samples.As a typical candidate,the cata-lyst pyrolyzed at600°C was selected as the target analysis ma-terial.Fig.7(a,b)shows the N1s binding energy region,where the peaks of N1s at398.9and400.5eV can be attributed to pyridinic-N and pyrrolic-N(or pyridone-N),respectivity.8,21 It should be mentioned that pyridinic-N is a type of nitrogen that contributes one p-electron to the aromatic p-system and has a lone electron pair in the plane of the carbon matrix.The pyridinic-N can be found on the edge of a carbon plane and a carbon vacancy.Since the pyridinic-N has a lone electron pair in the plane of the carbon matrix,this can increase electron-donor property of the catalyst,and thus weaken the O―O bond via the bonding between oxygen and nitrogen and/or the adjacent carbon atom,and facilitate the reduction of oxygen.In other words,the pyridinic N species may have converted the ORR reaction mechanism from a2e-dominated process to a 4e-dominated process and improved the ORR onset potential. While pyrrolic-N atoms are incorporated into five-membered heterocyclic rings,where each N atom is bonded to two carbon atoms and contributes two p-electrons to theπsystem.Al-though some progresses toward the identity and role of the electrocatalytic active center have been made,the precise rela-tionship between catalytic activity and nitrogen species,is still unclear.22From the Fig.7(a,b),we know that increasing the thermal treatment temperature transforms more of the pyridinic nitrogen to pyrrolic nitrogen,where Fe-N/C-TsOH heat-treated at600°C has larger fraction of the pyrrolic nitrogen groups compared to the pyridinic nitrogen groups,and it shows the higher activity than the catalyst unpyrolyzed as CVs and RDE results showed(Fig.1and Fig.2).This indicates that the pyrro-lic nitrogen group is more active for oxygen reduction and the catalyst pyrolyzed at600°C has more active sites(pyrrolic ni-trogen)to facilitate oxygen adsorption.The result agrees well with the reports that pyrrolic nitrogen is responsible for the unique activity of Fe-containing catalysts which was claimed earlier.23In addition,the preferred protonation of pyridinic sites may explain why higher heat-treatment temperature,which leads to more pyrrolic nitrogen and less pyridinic nitrogen,24re-sults in more stable catalysts.25Fig.7(c)shows the S2p XPS spectra measured for unpyrolyzed catalyst samples.It can be seen that the catalyst without thermal treatment shows a large band at167.0-171.0eV,which could be assigned to sulfate in catalyst precusor.14,16After pyrolyzed at600°C,the deconvolu-tion of the S signals gave two bands with binding energies of 163.8and168.8eV,as shown in Fig.7(d).These peaks could be attributed to the binding sulfurs in C―S n―C(n=1,2) bonds and oxidized―SO n―bonds,which are expected to oc-cur at the edges of carbon.26,27Guo et al.28found that―C―S―C―plays the key role in promoting the ORR.The fact may ex-plain the result that the catalyst pyrolyzed at600°C shows bet-ter catalytic activity for the ORR as demonstrated in this work. It is believed that pyrolysis of the catalyst in the presence of sulfur could lead to amorphous carbon,resulting in an in-creased catalyst porosity and in turn enhanced catalyst perfor-mance.16,29,30Besides,sulfur group doped into the M-N x-C might be helpful for entrapping M ions in an environment rich in pyr-role-type nitrogen.Thus,it was surmised that not only nitrogen doping but also sulfur doping of carbon play a key role in
im-
Fig.7XPS spectra of deconvoluted(a,b)N1s and(c,d)S2p for Fe-N/C-TsOH catalyst
(a,c)unpyrolyzed;(b,d)pyrolyzed at600°C
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proving electrocatalytic activity of the ORR.
4Conclusions
In short,non-noble metal Fe-N/C electrocatalysts were pre-pared without and with TsOH dopant.The dual-doped catalysts show better catalytic activity for the oxygen reduction in alka-line solution than the catalysts doped only with N in terms of on-set potential,half-wave potential,as well as limited current potential values.The percentage of H2O2produced in the poten-tial range for Fe-N/C-TsOH were less than15%,while50%for Fe-N/C-None,indicating a difference in the mechanisms cata-lyzed by these two catalysts.Furthermore,the catalytic activity strongly depended on the thermal temperature for the catalyst synthesis,and the best ORR performance was obtained at600°C. In particular,E onset and the potential at the current density of-1.5 mA?cm-2for Fe-N/C-TsOH-600H are30and170mV more posi-tive than Fe-N/C-TsOH-RT,respectively.Instrumental analysis and the SEM,XRD,and XPS results all showed that most of the active sites were formed after the samples were pyrolyzed at600°C.
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Fe-N/C-TsOH催化剂应用碱性介质催化氧还原的电催化活性
作者：徐莉， 潘国顺， 梁晓璐， 罗桂海， 邹春莉， 罗海梅， XU Li， PAN Guo-Shun， LIANG Xiao-Lu， LUO Gui-Hai， ZOU Chun-Li， LUO Hai-Mei
作者单位：清华大学摩擦学国家重点实验室，北京100084; 深圳清华大学研究院深圳市微纳制造重点实验室，广东深圳518057
刊名：
物理化学学报
英文刊名：Acta Physico-Chimica Sinica
年，卷(期)：2014(2)
本文链接：https://www.doczj.com/doc/c37518487.html,/Periodical_wlhxxb201402018.aspx
Advances in Material Chemistry 材料化学前沿, 2015, 3(4), 61-67 Published Online October 2015 in Hans. https://www.doczj.com/doc/c37518487.html,/journal/amc https://www.doczj.com/doc/c37518487.html,/10.12677/amc.2015.34007 文章引用: 汪广进, 刘海, 龚春丽, 程凡, 文胜, 郑根稳. 氧化锆基催化剂的制备及其氧还原催化性能研究进展[J]. 材 Study Progress on the Preparation and Catalytic Performance of Zirconia for Oxygen Reduction Reaction Guangjin Wang, Hai Liu, Chunli Gong, Fan Cheng, Sheng Wen *, Genwen Zheng College of Chemistry and Materials Science, Hubei Engineering University, Xiaogan Hubei Received: Nov. 12th , 2015; accepted: Dec. 26th , 2015; published: Dec. 29th , 2015 Copyright ? 2015 by authors and Hans Publishers Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). https://www.doczj.com/doc/c37518487.html,/licenses/by/4.0/ Abstract Development of non-platinum catalysts for the renewable energy is urgent. Due to the excellent chemicaland electrochemical, zirconia is attracting abroad attention in the investigation of novel non-platinum catalysts. Therefore, this paper reviews the status of the preparation methods such as magnetron sputtering and dip-coating for zirconia, and summarizes the study progress of the non-stoichiometry zirconia, transition metal/non-transition metal doped zirconia, partially oxi-dized zirconium carbonitrides and pyrolyzed zirconium base chelates. At last, this paper also looks ahead at the development of zirconia based non-pltinum catalysts. Keywords Non-Platinum Metal Catalysts, Zirconia, Preparation Methods, Oxygen Reduction Reaction 氧化锆基催化剂的制备及其氧还原催化性能 研究进展 汪广进，刘 海，龚春丽，程 凡，文 胜*，郑根稳 湖北工程学院化学与材料科学学院，湖北 孝感 *通讯作者。
[Article] https://www.doczj.com/doc/c37518487.html, 物理化学学报(Wuli Huaxue Xuebao ) Acta Phys.?Chim.Sin .2012,28(12),2879-2884 December Received:July 5,2012;Revised:September 13,2012;Published on Web:September 25,2012.? Corresponding author.Email:zfma@https://www.doczj.com/doc/c37518487.html,;Tel:+86-21-54742894. The project was supported by the National Natural Science Foundation of China (21073120,21176155)and Science and Technology Foundation of Shanghai Municipality,China (10JC1406900). 国家自然科学基金(21073120,21176155)及上海市自然科学基金(10JC1406900)资助项目 ?Editorial office of Acta Physico ?Chimica Sinica doi:10.3866/PKU.WHXB 201209252 铂/石墨烯氧还原电催化剂的共还原法制备及表征 王万丽 马紫峰* (上海交通大学化学工程系,上海200240) 摘要: 使用硼氢化钠共还原法制备40%(w )铂/石墨烯电催化剂用于氧还原反应.通过循环伏安测试发现,这 种方法制备所得铂/石墨烯催化剂对氧还原反应活性较铂/碳催化剂差,但稳定性有所提高.在稳定性测试中,铂/石墨烯电催化性能衰减为50%,较铂/碳(79%)好.X 射线衍射(XRD)和透射电子显微镜(TEM)表征发现在铂/石墨烯催化剂中两者存在明显交互作用,这可能是阻止石墨烯再堆垛和防止铂颗粒团聚的主要原因.通过对单电池性能测试也发现铂/石墨烯催化剂更有利于电池长期稳定.关键词: 石墨烯;共还原法;电催化剂;氧还原反应;质子交换膜燃料电池 中图分类号: O646 Synthesis and Characteristics of Pt/graphene by Co-Reduction Method for Oxygen Reduction Reactions WANG Wan-Li MA Zi-Feng * (Department of Chemical Engineering,Shanghai Jiao Tong University,Shanghai 200240,P .R.China ) Abstract:40%(w )Pt/graphene composites were prepared by sodium borohydride chemical co-reduction,and were subsequently used as an electrocatalyst for oxygen reduction reactions.The electrocatalytic activity and stability was evaluated by cyclic voltammetry.The results indicated that the initial activity of Pt/graphene was lower than that of Pt/C due to the oxygen diffusion inhibition;however,the Pt/graphene showed superior durability characteristics.Degradation tests showed a 50%degradation of Pt/graphene,which was substantially less than that of Pt/C (79%).X-ray diffraction and transmission electron microscope results showed that the composite formed strong interactions between the platinum nanoparticles and the graphene supports.The graphene supports may also prevent the graphene sheets from folding or re-stacking,which would hinder platinum nanoparticles ?aggregation.The performance of a single cell was also tested,confirming an improvement in durability.Key Words:Graphene; Co-reduction method; Electrocatalyst; Oxygen reduction reaction; Proton exchange membrane fuel cell 1Introduction Gaphene has attracted great attention from researchers in both theoretical and applied chemistry in recent years.Its use has also been studied in capacitors,1,2lithium batteries,3-6and fuel cells 7-9because of its interesting properties,such as ultra-high surface area (there is a theoretical surface area of 2620 m 2·g -1for an isolated graphene sheet),special quantum proper-ties 10-13and so on. Proton exchange membrane (PEM)fuel cells have been de-veloped as a promising energy technology because of their in-herent advantages,such as simplicity,viability,and quick start-up,which give them of great potential in almost any con- 2879
第４３卷 第２期２０１５年３月 河南师范大学学报（自然科学版） Ｊｏｕｒｎａｌ ｏｆ Ｈｅｎａｎ Ｎｏｒｍａｌ Ｕｎｉｖｅｒｓｉｔｙ（Ｎａｔｕｒａｌ Ｓｃｉｅｎｃｅ Ｅｄｉｔｉｏｎ） Ｖｏｌ．４３ Ｎｏ．２ Ｍａｒ．２０１５ 文章编号：１０００－２３６７（２０１５）０２－００７４－０６ ＤＯＩ：１０．１６３６６／ｊ．ｃｎｋｉ．１０００－２３６７．２０１５．０２．０１４氮掺杂石墨烯的制备及其氧还原电催化性能 石 敏，张 庆，牛 璐，晁淑军，黄茹梦，白正宇 （河南师范大学化学化工学院；绿色化学介质与反应教育部重点实验室，河南新乡４５３００７） 摘 要：以三聚氰胺和氧化石墨烯（ＧＯ）为原料，经物理研磨和高温热解得到氮掺杂石墨烯（三聚氰胺－ＮＧ）．扫描电子显微镜（ＳＥＭ）测量显示，所制备的三聚氰胺－ＮＧ厚度和表面褶皱较掺杂前略有增加．Ｘ射线光电子能谱（ＸＰＳ）表明，在三聚氰胺－ＮＧ中氮元素以吡咯Ｎ、吡啶Ｎ和石墨Ｎ ３种形式掺杂在石墨烯中，它们的比例分别是１４．５％、２４．５％和６１．０％．同时运用循环伏安法（ＣＶ）和旋转圆盘电极技术（ＲＤＥ）测试了三聚氰胺－ＮＧ在碱性介质中的氧还原电催化活性．结果表明，与商业石墨烯和由聚吡咯为氮源制备的氮掺杂石墨烯（ｐｐｙ－ＮＧ）相比，三聚氰胺－ＮＧ具有较高的电催化活性和较正的氧还原起始电位（－０．０９Ｖ），并且电催化还原氧气时主要为４电子反应．由于其较高的氧还原性能和较低的成本，三聚氰胺－ＮＧ在碱性燃料电池阴极电催化剂中有良好的应用前景．关键词：氮掺杂石墨烯；三聚氰胺；氧还原；燃料电池 中图分类号：Ｏ６１４文献标志码：Ａ 燃料电池是一种将燃料的化学能按电化学方式等温地转化为电能的发电装置，其中氧还原反应缓慢的动力学过程是影响燃料电池能量转换效率的重要因素之一．到目前为止，最有效的阴极催化剂是贵金属及其合金催化剂［１－２］．然而，贵金属价格昂贵，在催化剂成本中占有很大的比重，其催化活性和稳定性也需要进一步提高，极大地影响了低温燃料电池产业化进程［３］，因此开发成本低廉的新型非贵金属催化剂，成为燃料电池研究人员近年来努力的重要方向之一［４］． 石墨烯是由ｓｐ２杂化碳原子相互连接构成的仅一个原子厚度的二维平面材料，其碳原子构成六角环形蜂窝状，该特殊晶格结构赋予石墨烯优异的物理和化学性质［５－６］．目前，石墨烯已成为许多领域的研究热点，如催化剂载体［７］、电池［８］、传感器［９］以及储氢材料［１０］等．理论计算和相关实验结果均表明，在石墨烯ｓｐ２杂化的碳原子中引入氮原子可以有效提高其电化学活性，这是由于掺杂的氮原子会影响石墨烯中碳原子的自旋密度和电荷分布，使氮原子周围的碳原子带有更多的正电荷，导致石墨烯表面产生“活性位点”，这些“活性位点”可以直接参与氧还原催化反应（ＯＲＲ）［１１］．综合文献报道，与商品Ｐｔ／Ｃ催化剂相比，氮掺杂石墨烯（ＮＧ）作为不含金属元素的氧还原催化剂具有较高的催化活性和电化学稳定性，Ｚｈａｎｇ等［１２］利用密度泛函理论对氮掺杂石墨烯上氧还原反应的机理进行理论模拟，所得结果与实验观察一致，即在ＮＧ上ＯＲＲ是一个直接的４电子途径．因此，ＮＧ被广泛认为是贵金属催化剂的理想替代材料之一［１３］． 本文采用常见且廉价的三聚氰胺为氮源，在不影响石墨烯片层结构的基础上，经过物理研磨后高温煅烧合成出氮掺杂石墨烯（三聚氰胺－ＮＧ），对比研究了不同Ｎ掺杂形式及不同Ｎ含量石墨烯的氧还原反应催化性能，结果表明，吡啶－Ｎ和石墨－Ｎ含量较高的三聚氰胺－ＮＧ催化剂对氧还原反应表现出较高的电催化性能． １ 实验部分 １．１ 仪器和试剂 三聚氰胺（分析纯，沈阳化学试剂厂）；吡咯（分析纯，国药集团化学试剂有限公司）；商业石墨烯（合肥微 收稿日期：２０１４－１１－１０；修回日期：２０１５－０３－１１． 基金项目：国家自然科学基金（２１３０１０５１）；河南省基础与前沿研究项目（１３２３００４１００１６）；河南师范大学青年基金项目．作者简介：白正宇（１９７９－），女，河南濮阳人，河南师范大学副教授，博士，主要从事燃料电池催化剂的研究． 通信作者：白正宇，河南师范大学化学化工学院，Ｅ－ｍａｉｌ：ｂａｉｚｈｅｎｇｙｕ２０００＠１６３．ｃｏｍ．
Fe-N/C氧还原电催化剂的设计制备及性能研究电化学氧还原反应在燃料电池和金属-空气电池等可再生能源储存和转换系统中扮演着重要作用。缓慢的氧还原反应动力学需要催化剂。到目前为止,铂贵金属是活性最高的氧还原催化剂。 然而,昂贵的价格,对甲醇和CO敏感和稳定性差阻碍其大规模广泛应用。为突破这个瓶颈,很多研究工作致力于探索具有高活性和稳定性的非贵金属催化剂。在已发现的不含贵金属的催化剂中,过渡金属和氮掺杂的碳材料(M-N/C)被认为 是特别有前途的氧还原催化剂,因为它们的元素丰度高、低成本、低环境影响和较高的活性。 本论文主要主要是针对铁和氮共掺杂碳材料的设计、合成和性能进行了深入研究。本论文具体内容如下:选择两端含吡啶氮的有机分子btcpb作为配体与铁(Ⅱ)配位,形成类似配位聚合物的配合物,在不需要外加碳载体的情况下,煅烧得到自支撑Fe-N/C催化剂。结果表明,700℃煅烧的催化剂(Fe-N/C-700)活性最好。 碱性条件下,半波电势840 mV,高于商业铂-碳催化剂;酸性条件下,起始电位和半波电位均可比与商业Pt/C催化剂。同时,该催化剂在碱性和酸性溶液中都显示了优异的循环稳定性和良好的甲醇耐受性能。除此之外,该材料充当锌-空电池的空气阴极,在5 mA cm-2电流密度时,电池的容量达到727 mA hg-1。 持续放电110 h,也没有明显电压损失,表明该材料具有很强的应用前景。报道了 Fe3C纳米颗粒修饰,金属铁和氮掺杂碳的复合物的简单高效大规模制备, 以铁-邻菲罗琳配合物和二氰二胺为前驱物,高温煅烧。800 ℃条件下得到的催化剂显示出极好的氧还原活性,碱性溶液中的起始电位和半波电位高达0.99和 0.86 V,远高于商业铂-碳。
氧还原催化剂的制备及电化学性能的研究 摘要：随着环境问题越来越引起人们的关注，环境保护已成为可持续发展的核心。全球都致力于研究高效节能环保的新型能源。燃料电池是一种可以高效地将燃料和氧化剂转化为电能的发电装置。世界经济和科技的日益发展离不开能源。随着现代社会在工业、农业、科技、信息技术等各个方面的飞速发展，石油、天然气、煤等不可再生的常规能源消耗已经日渐殆尽，同时常规能源使用排放的有毒有害物质引发的环境问题、生态问题也随之加剧。因此，幵发新能源、环保能源具有重大深远的意义，势必成为当今科研的主流趋势。本文就氧还原催化剂的制备及电化学性能进行分析与研究 关键词：氧还原催化剂；制备；电化学性能 引言 氧还原反应是众多新型电池正极电极所发生的过程。促进其反应过程一直以来是电化学领域研究的侧重方向，故而开发和研究氧还原催化剂性能的工作显现出极高的科研价值和应用价值。做为众多电化学工作者的研究热点，电催化氧还原技术具备广泛的应用范围，长期以来，由于电化学催化氧还原技术在燃料电池、微生物燃料电池、高级电氧化技术、水处理等方面越来越多的应用，使化学修饰电极电催化领域得到普遍关注。催化剂在电极表面的氧还原反应中起到了非常重要的作用，制备一种高性能、低成本、对环境友好的催化剂是非常有价值的。 一、氧还原反应 在氧还原电极上，氧发生的还原反应是个复杂的过程，氧还原反应涉及4个电子及2～4个质子的转移，和0-0键的断裂，由于其复杂性，可以写出各种各样的反应机理。通常，依照中间产物过氧化氢（H2O2)的生成与否，其历程主要包括两类： 1.直接四电子反应途径：此类途径并没有可检测的过氧化氢。0-0键在吸附氧分子时断裂变为吸附氧原子MO，在酸性溶液中，氧分子持续得到四个电子还原为H2O，在碱性溶液中，还原为OH-。 在酸性介质中： 02+4H++4e →2H20, E=1.229V 在碱性介质中： 02+2H20+4e →40H，E=0.401V 2.间接二电子反应途径：在碱性溶液中，碳、石墨、金、汞等电极上02还原主要是此途径，其过程有中间产物过氧化氢生成，在氧分子吸附时先得到两电
§7.1 氧化还原反应的基本概念 ?氧化还原反应由氧化反应和还原反应两个半反应组成 一、氧化态 ?定义：氧化态（氧化数）是元素一个原子的形式电荷，这种形式电荷是由假设两个键中的电子指定给电负性更大的原子而求得（以化合价为基础） ?氧化态是按一定规则（人为规定）指定的形式电荷的数值（可以是负数、正数、零or分数）。 二、确定氧化态的规则 1. 离子型化合物中，元素的氧化数等于该离子所带的电荷数 2. 共价型化合物中，共用电子对偏向于电负性大的原子，两原子的形式电荷数即为它们的氧化数 3. 单质中，元素的氧化数为零；离子Xn-氧化数为n- 4. 中性分子中，各元素原子的氧化数的代数和为零，复杂离子的电荷等于各元素氧化数的代数和 5. 氢的氧化数一般为+1，在金属氢化物中为-1，如NaH 6. 氧的氧化数一般为(-II)，例外有-I、+I、+II等，在过氧化物中为-1，如Na2O2 ，在超氧化物中为-0.5，如KO2 ，在氧的氟化物中为+1或+2，如O2F2 和OF2中 7. 氧化数可以是分数Fe3O4(Fe2O3·FeO)，Fe的氧化数为8/3，可见是平均氧化数 ?氧化数、化合价、化学键数的区分 §7.2电化学电池 一、原电池 ?借助于氧化还原反应将化学能直接转变成电能的装置。理论上，任何氧化还原反应都可以设计为原电池。 ?要求：(1) 自发氧化还原反应 (2)装置，氧化过程和还原过程分别在不同的电极上进行，电极之间要通过导线和盐 桥连接。 ?盐桥：饱和的电解质溶液。如KCl 溶液。 ?目的：保持溶液电中性——由于K＋和Cl－的定向移动，使两池中过剩的正负电荷得到平衡，恢复电中性。于是两个半电池反应乃至电池反应得以继续，电流得以维持。 ?原电池装置可用简单的符号表示，称为电池图示。 例：Daniell电池的电池图示——(-) Zn | Zn2+(c1) ||Cu2+(c2) | Cu (+) ?原电池符号的要求: (1) 负极在左，正极在右 (2) 按顺序排列各物质，两相之间的界面用“ | ”隔开 (3) 盐桥用“||”表示 (4) 溶液需标出浓度，气体需标出压力 §7.3电极电势 一、原电池的电动势 原电池的电动势E MF等于正极的电极电势E(+)减去负极的电极电势E(-) 。E MF可以用电位差计测得。E MF= E(+)- E(-) ?E MF —电动势E MFθ—标准电动势E MFθ= E(+)θ- E(-)θ 二、标准氢电极和甘汞电极 1、标准氢电极：涂满铂黑铂丝作为极板，插入到H＋(1 mol·dm－3 )溶液中，并向其中通入H2
第十七次全国电化学大会1磷掺杂石墨烯的制备及氧还原催化性能 李容1,2，魏子栋1,*，苟兴龙2,* (1.重庆大学化学化工学院，重庆，400044，E-mail:zdwei@https://www.doczj.com/doc/c37518487.html,; 2.西华师范大学化学化工学院，四川，南充，637000，E-mail:gouxlr@https://www.doczj.com/doc/c37518487.html,) 燃料电池是一种高效新型能源转换装置，具有能量密度高、能量转换效率大、零排放、环境友好等优点。但是，燃料电池的阴极氧还原反应（ORR ）的过电位大、动力学性能差，需要大量昂贵的铂基催化剂。而且，这类催化剂不抗甲醇氧化和一氧化碳中毒，稳定性差，限制了燃料电池的规模化生产和应用。因此，研发成本低、活性高、稳定性好的非贵金属和非金属氧还原催化剂是当前燃料电池技术发展与应用的关键[1]。 杂原子（如氮、磷、硼、硫、碘等）掺杂的碳纳米材料比表面积大、活性高，可望替代铂基催化剂，成为燃料电池氧还原催化剂的研究热点[2,3]。石墨烯是一种由碳原子构成的单层片状结构碳材料，其导电性、比表面积等远远优于普通碳材料[4]。但是，鲜见报道磷掺杂石墨烯的制备及氧还原催化性能。我们通过热解氧化石墨和1-丁基-3-甲基咪唑六氟磷酸盐离子液体混合物制备了磷掺杂石墨烯（P-TRG ）[5]。该合成方法简单、环境友好、易于控制。所得P-TRG 催化剂保持了石墨烯纳米片的形貌（图1a ），比表面积大（496.67m 2/g ）、磷含量高（1.16at.%）、ORR 催化活性高，起峰电位和还原电流与商品铂碳相当（图1b ），而且在抗甲醇和一氧化碳中毒、稳定性方面显著优于商品铂碳催化剂。 图1P-TRG 的TEM （a ）和ORR 线性伏安图（b ） Fig.1TEM image (a)and LSV curves (b)of the P-TRG sample. 本研究为973计划（2012CB215500,2012CB720300）和国家自然科学基金（21176327,51071131,20936008）资助项目。 参考文献： [1]Cheng.F,Chen.J.Chem.Soc.Rev.,2012,41,2172. [2]Li.Y,Zhou.W,Wang.H,Xie.L,Liang.Y,Wei.F,Dai.H.J.Nat.Nanotechnol .,2012,7,394. [3]Shao.L.Chen.J,Bao.W,Wang.F,Xia.X.ACS Nano ,2011,5,4350. [4]Sun.Y,Wu.Q,Shi.G.Energy Environ.Sci .,2011,4,1113. [5]Li.R,Wei.Z.D,Gou.X.L,Xu.W.RSC Advances 2013,3,9978. Synthesis and Electrocatalytic Performance of Phosphorus-Phosphorus-d d oped G raphen e for Application in O xygen R eduction Reaction Rong Li ,1,2Zidong Wei,1,*Xinglong Gou 2,* (1College of Chemistry and Chemical Engineering,Chongqing University,Chongqing 400044,E-mail: zdwei@https://www.doczj.com/doc/c37518487.html, 2College of Chemistry and Chemical Engineering,China West Normal University,Nanchong 637000,E-mail: gouxlr@https://www.doczj.com/doc/c37518487.html, )
氧还原催化剂研究进展 摘要 虽然经过半个多世纪对研究,人们对氧电极反应取得了很多原子、分子水平上的认识,但是对氧还原的高超电势的起源、催化剂的氧还原活性与结构的内在关系等问题,?还没有清晰的认识。其主要原因是一方面氧还原反应是一个涉及4电子转移、多步骤的复杂反应,人们在研究中并没有仔细考究常用于研究纳米电催化剂的氧还原反应活性的薄膜旋转圆盘电极技术是否切实可靠。 非贵金属氧还原催化剂是近年来低温燃料电池最受关注的研究热点之一。本文回顾了燃料电池用非贵金属氧还原催化剂方面的研究进展，总结了提高催化活性和稳定性、降低催化剂制备成本、催化剂制备工艺和新型非贵金属氧还原催化剂设计等方面所取得的研究结果。对非贵金属氧还原催化剂亟待解决的问题和发展趋势提出自己的看法。 关键词：燃料电池；非贵金属催化剂；氧还原反应；电化学性能 Abstract However, no consensus on ORR mechanism and key factors which
limits ORR ki'netics has been reached so far.This is probably due to, on one hand, ORR is a reaction involves 4 electron, multiple step complex process, on the other hand, some misunderstanding exists on using thin film rotating disk electrode method, the key technique used for evaluating nanocatalysts activity for ORR. In recent years，non-precious metal oxygen reduction catalysts have gained particular interest for fuel cells. This paper presents the research progress of non-precious metal oxygen reduction catalysts with focus on the effort to improve the activity and durability of the catalysts，to decrease cost of the catalysts，and to develop novel non-precious metal catalysts. The urgent problems and future research focuses for non-precious metal oxygen reduction catalysts are also proposed. Key words：fuel cells；non-precious metal catalysts；oxygen reduction reaction；electrochemical performance 一、绪论 1.1氧还原电催化研究背景
第六章 氧化─还原反应和电化学 Chapt e r 6 Oxidation-Reduction Reactions & Electrochemistry 本章研究另一类化学反应──氧化─ 还原反应（有电子转移的反应） §6-1 氧化─ 还原反应 Oxidation —Reduction Reactions 一、氧化数（Oxidation Number ） 1．氧化数是一个经验值，是一个人为的概念。 2．引入此概念，有以下几方面的应用： (1) 判断是否发生氧化──氧化数升高、氧化反应、还原剂 reducing agent ( reductant )；氧化数降低、还原反应、氧化剂 oxidizing agent ( oxidant )。 (2) 计算氧化──还原当量 (3) 配平氧化──还原反应方程式 (4) 分类化合物，如Fe ( Ⅲ )、Fe (Ⅱ)；Cu (Ⅰ)、Cu (Ⅱ)。 引入氧化数，可以在不用详细研究化合物的结构和反应机理的情况下，实现上述四点。 3．怎样确定氧化数 (1) 在离子化合物中，元素的氧化数等于离子的正、负电荷数。 (2) 在共价化合物中，元素的氧化数为两个原子之间共用电子对的偏移数。 a ．在非极性键共价分子（单质）中，元素的氧化数为零，如P 4、S 8、Cl 2中P 、S 、Cl 的氧化数都为零； b ．在极性键共价分子中，元素的氧化数等于原子间共用电子对的偏移数，例如： 1 1 H :F +-，1 1 11 (-2) H :O :H +--+，11 0011(1) H :O :O:H +--+-，11 +11 (0) H ::F O +--。 (3) 具体规定： a ．单质的氧化数为零，例如P 4、S 8中P 、S 的氧化数都为零，因为P －P 和S －S 键中共用电子对没有偏移； b ．除了在NaH 、CaH 2、NaBH 4、LiAlH 4中氢的氧化数为-1以外，氢的氧化数为 +1； c ．所有氟化物中，氟的氧化数为-1； d ．氧的氧化数一般为-2，但有许多例外，例如2O (1/2)--、22O (1)- -、 3O (1/3)--、21/2O ()++、2OF 2)(+等； 目前元素的最高氧化数达到+8，在OsO 4、RuO 4中，Os 和Ru 的氧化数均为 +8，其它元素的最高氧化数至多达到其主、副族数。例如：Na 2Cr 2O 12和CrO 5 中，Cr 的氧化数为+6，因为这些化合物中有22O - （O 的氧化数为-1）存在； e ．在配合物中，当自由基或原子团作为配体时，其氧化数均看作-1：CH 3(-1)、
银纳米线的制备及电催化还原氧性能研究 摘要:分别以聚乙烯基吡咯烷酮( PV P),乙二醇作为软模板和还原剂,采用不同晶种( A gC lAg )快速合成了银、纳米线.通过SEM和TEM表征,证明合成银纳米线材料形貌均一,颗粒含量很少.并且发现以A gC l为晶种合成 的银纳米线长径比为200左右( SNWH ),而以A g为晶种合成的长径比为30左右( SNW L ) .以银纳米线作为电催化氧气还原反应( ORR )的催化剂.通过循环伏安法测定,发现银纳米线对氧还原具有显著的活性,反应起始还原电压为- 0. 17 V左右,还原峰电压为- 0. 45V左右,并且反应受O 2扩散的控制.研究表明两种长径比的银纳米线 均对醇类有一定的抵抗力.如对于SNW H,当甲醇含量为2. 0 mo l/L或乙醇含量为0. 5 mo l/L时,电催化ORR仍 具有较高的活性.比较不同的醇类对于银纳米线电催化ORR,发现醇类对反应的影响的顺序如下:甲醇<乙醇< 异丙醇. 关键词:银纳米线;长径比;氧气还原;抗醇 [ 17] 无论是氢氧燃料电池还是醇类燃料电池的阴极相比P t /C催化剂具有很强的抗醇性能. 反应均为氧气还原反应( ORR ) . ORR是一个多电 子的复杂反应.目前P t基催化剂(如P tV, P tCo, P tF e P tN i等)被认为是电催化ORR反应最好的, [ 1] 催化剂.但是由于P t的价格昂贵,如何降低催化 [ 2- 3 ] 剂中P t的含量,提高P t的利用率,和以其他 较为廉价的材料代替P t开发非P t基的催化剂成为 [ 4- 9 ] 研究的热点.在酸性介质中,一些非P t材料没 有活性或者活性很小,但其在碱性电解质中却可以 [ 10] 催化氧气还原反应. 另外由于在甲醇或乙醇等醇类燃料电池中,甲 醇或乙醇会不可避免的渗入到阴极区域,而P t在 催化氧气还原和催化醇类反应时,没有选择性.这 样就会影响P t基催化剂电催化氧气还原的活性.因此,醇类燃料电池中的具有抗醇性能的阴极催化 剂的研究极为重要.目前研究的具有抗醇能力的阴 极催化剂有RuSe x , Co 3 S 4 , P tB i ,金属卟啉配合物 2 [ 11- 16] 等等. Ag作为一种廉价以及对氧气还原反应 的较高活性,有很好的应用潜力,所以Ag基催化 [ 17- 18] 剂的研究在近年来受到了一定的重视. 2004 年, L. Dem arconnay等人将Ag /C用于氧气还原反应,发现Ag /C具有电催化氧气还原的活性,同时 目前,关于纳米粒子的形貌对氧气还原反应的 [ 19 20 ] , 影响的研究还比较少,对银纳米粒子形貌方 面的则更少.本文研究了银纳米线在燃料电池的阴 极和阳极上的催化性能.发现银纳米线在碱性条件 下没有电催化氧化甲醇的能力,但是具有电催化还 原氧气的能力,说明银纳米线对于氧气还原与甲醇 氧化反应具有选择性,具有抗醇性能.并且比较了 不同长径比的银纳米线的催化活性以及对于甲醇、 乙醇、异丙醇等醇类的抵抗能力. 1实验部分 高长径比的银纳米线( SNWH )利用下述方法制备.配制10 mL浓度为0 36 mo l /L PVP的乙二醇. ( EG)溶液,于圆底烧瓶中加热至170,回流1 h , 溶液由无色渐渐变为棕色.然后加入10L, 0 1 m ol /L N aC l的EG溶液,回流5m in 接着加入浓. .度为0 06 m ol /L的AgNO 3的EG溶液10L,回流5 . m in 得到AgC l的晶种.而后匀速滴加10 mL浓度为, 0 06 mo l/L AgNO 3的EG溶液, 5~ 7 m in 内滴加完.. 在170下,继续回流15 m in 溶液颜色先是加深,, 逐渐变成深棕色,然后变为灰白色.整个反应过程剧 烈搅拌,而后静置过夜,将上层EG悬浊液到出,得 到瓶底的灰白色沉淀,加入无水乙醇洗涤,将沉淀分散到无水乙醇当中.在2000 rp 离心分离15 m in m,沉淀再用无水乙醇洗涤,如此反复洗涤离心3次,将包裹在银纳米线表面的残留PVP洗去,最后将得到的银纳米线分散到无水乙醇中.低长径比的银纳米线( S L)的制备与SNWH的制备方法相似,只是NW 省略添加NaC l的EG溶液和回流步骤.株式会社),加速电压分别为5 kV.透射电子显微 镜表征( TEM )和电子衍射表征采用JEOL - 1200EX 显微镜(日本电子光学公司) ,加速电压为80 kV. 在D /m axRB型X射线衍射仪( Ph ilips)上测定催化剂XRD谱图,采用Cu K射线( 0. 15418 nm ),管 压为50 k 电流为60 mA,扫描速度0 5/m in, 2V,. 为30~ 80. UVv is光谱测试采用H P8453型UV v is 分光光度计( HP ) . 将直径为3 mm的玻碳电极( GC) ,按先后顺序
工作原理 电催化氧化技术的基本原理是使污染物在电极上发生直接电化学反应或利用电极表面产生的强氧化性活性物种使污染物发生氧化还原转变，后者被称为间接电化学转换。 直接电化学转化通过阳极氧化可使有机污染物和部分无机污染物转化为无害物质，阴极还原则可从水中去除重金属离子。这两个过程同时拌生放出H2与O2的副反应，使电流效率降低，但通过电极材料的选择和电位控制可加以防止。间接电化学转化可利用电化学反应产生的氧化还原剂C使污染物转化为无害物质，这时候C是污染物与电极交换电子的中介体。C可以是氧化还原媒质催化剂，也可以是电化学产生的短寿命中间物。 由于电化学氧化过程本身的复杂性，不同的研究者针对不同的有机物降解过程提出了不同的氧化机理，但人们普遍认为在电催化体系中有强氧化性的活性物种存在，这些强氧化性物种的存在能够大大提高降解有机污染物的能力，表1 列出了部分在电催化体系中可能产生的强氧化性活性物种及其标准还原电极电势。从表中可以看出，他们都具有相当高的还原电势，因此能够氧化大多数有机污染物。 表1 电催化体系中的强氧化性活性物种及其标准还原电极电势 种类标准电位（对甘汞电极S HE）/V 强氧化剂种类 标准电位（对甘汞电极SH E）/V OH· 2.8H2O2 1.78 O2- 2.42HO2 1.70 O3 2.07CI 1.36 设备优势 直接氧化和间接氧化协同作用，氧化能力强，能氧化难降解生化的有机物；在大幅度去除COD的同时，也能有效去除氨氮，同时提高废水的可生化性，大大降低后续处理的负担； 对于化工废水COD和氨氮难于达标，用于深度处理可同时去除COD和氨氮，保证系统稳定达标； 占地面积小，废水停留时间短，处理过程快，条件温和； 可靠性好，电解过程需控制的参数只有电流和电压，易于实现自动控制； 不需要外加药剂，不产生二次污染，是典型的“环境友好”型高级氧化技术。 应用范围 适用于高浓度难降解化工废水预处理，可直接降解COD和将高分子结构有机物降解为易生物降解的小分子有机物，提高BOD/COD比。 适用于难降解化工废水生化后深度处理，可将不可生化的有机物直接氧化成二氧化碳和水，并氧化去除氨氮，达到深度处理COD和氨氮同时达标排放的目的。 适用于化工、印刷、垃圾渗滤液、机加工、医药中间体、制药、农药、染料、