原位XAFS表征雙金屬納米催化劑PtCo/C在工作狀態(tài)下的結(jié)構(gòu)變化

尚明豐 趙天天 鮑洪亮 段佩權(quán) 林 瑞 黃宇營 王建強(qiáng)

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原位XAFS表征雙金屬納米催化劑PtCo/C在工作狀態(tài)下的結(jié)構(gòu)變化

尚明豐1趙天天2鮑洪亮1段佩權(quán)1林 瑞2黃宇營1王建強(qiáng)1

1（中國科學(xué)院上海應(yīng)用物理研究所 張江園區(qū) 上海 201204）2（同濟(jì)大學(xué) 汽車學(xué)院 上海 201804）

用兩步還原法制備的PtCo/C (10 wt% Pt)納米催化劑具有與商業(yè)催化劑Pt/C (20 wt% Pt)接近的催化反應(yīng)活性，使貴金屬Pt的用量減少了50%。利用上海光源BL14W1線站的質(zhì)子交換膜燃料電池(Proton exchange membrane fuel cell, PEMFC)原位X射線吸收精細(xì)結(jié)構(gòu)譜(X-ray absorption fine structure, XAFS)實驗裝置，在以該PtCo/C作為燃料電池的陰極催化劑，以Pd/C作為陽極催化劑的條件下，原位表征PtCo/C在工作狀態(tài)下的結(jié)構(gòu)變化，PtCo/C的非原位XAFS數(shù)據(jù)沒有觀察到Pt?Co合金成分，發(fā)現(xiàn)存在顯著的Co?O鍵和Co?O?Co鍵貢獻(xiàn)，且與Pt/C相比，Pt的氧化程度更高且具有更短的Pt?Pt金屬鍵長，說明PtCo/C中的Co主要以氧化物種形式存在，且Co的存在影響著活性成分Pt的結(jié)構(gòu)。原位XAFS數(shù)據(jù)表明隨著電壓的逐漸降低，PtCo/C中Pt和Co的氧化程度降低，揭示了在催化反應(yīng)過程中Pt的d電子向過渡金屬Co的轉(zhuǎn)移過程。

質(zhì)子交換膜燃料電池，原位，X射線吸收精細(xì)結(jié)構(gòu)譜，結(jié)構(gòu)變化

由于其構(gòu)造簡單、能量密度高、能量轉(zhuǎn)化效率高、環(huán)境友好等優(yōu)點，作為化學(xué)電源被廣泛應(yīng)用[1?3]。純Pt具有催化活性高和穩(wěn)定性好等特點，是質(zhì)子交換膜燃料電池最常用的催化劑，但是Pt催化劑高昂的成本和較短的使用壽命極大地阻礙了其大規(guī)模的商業(yè)應(yīng)用[4]，因此在保證催化劑活性的前提下，減少Pt的使用量，提高燃料電池的耐久性就顯得尤為重要[5]。

作為質(zhì)子交換膜燃料電池的陰極發(fā)生的(Oxygen reduction reaction, ORR)，在化學(xué)反應(yīng)動力學(xué)上速度較慢，成為制約質(zhì)子交換膜燃料電池性能的關(guān)鍵，因此尋找活性更高、價格更便宜的陰極催化劑就成為研究的重點。在Pt中摻雜非貴金屬元素，如Fe、Co、Ni等，有助于提高Pt催化劑的穩(wěn)定性和催化活性，同時也減少Pt的使用量[6]。摻雜過渡金屬元素增強(qiáng)Pt催化PEMFC陰極氧化還原反應(yīng)活性的機(jī)理是：減小Pt?Pt鍵之間的距離（幾何效應(yīng)），形成更多具有5d空軌道的外層電子結(jié)構(gòu)，增強(qiáng)氧的π電子向Pt表面轉(zhuǎn)移（電子效應(yīng)）[7]。低Pt燃料電池催化劑的研究和應(yīng)用已有大量的報道，PtCo/C催化劑表現(xiàn)出較高ORR催化活性而受到廣泛關(guān)注[15?21]。

許多常用的表征方法如X射線衍射(X-ray diffraction, XRD)、線性掃描伏安法(Linear sweep voltammetry, LSVs)、循環(huán)伏安法(Cyclic Voltammetry, C-V)、透射電鏡(Transmission electron microscope, TEM)被應(yīng)用于PtMn(Fe,Co,Ni)/C雙金屬納米催化劑的研究[22?25]，但是不能獲得燃料電池催化劑在工作狀態(tài)下的結(jié)構(gòu)信息。近幾十年來，隨著同步輻射光源的建設(shè)，XAFS實驗技術(shù)得到廣泛的應(yīng)用。Ishiguro等[26]利用原位時間分辨XAFS譜，觀察到了Pt3M(M=Co, Ni)雙金屬納米催化劑在工作狀態(tài)下Pt?O鍵的斷裂和Pt?Pt的生成。Nagamatsu等[27]通過燃料電池的原位XAFS數(shù)據(jù)發(fā)現(xiàn)催化劑Au@Pt/C和Pd@Pt/C在催化反應(yīng)過程中Pt?O鍵的存在抑制了Pt的ORR催化活性。Greco等[28]借助于原位XAFS數(shù)據(jù)發(fā)現(xiàn)增加PtCo/C催化劑的化學(xué)和局域結(jié)構(gòu)的有序度并不能影響ORR的催化活性。上海光源BL14W1線站建立的PEMFC原位XAFS實驗方法，一方面利用XAFS技術(shù)觀察催化劑在反應(yīng)過程中的動態(tài)變化，另一方面同步監(jiān)測催化劑在工作狀態(tài)下電化學(xué)信息，進(jìn)而找到催化劑的性能變化和結(jié)構(gòu)變化的對應(yīng)關(guān)系[29]。

1 材料與方法

1.1 樣品的制備

催化劑的制備

采用兩步還原法制備PtCo/C，首先納米Co顆粒通過NaBH4還原CoCl2制備，然后Pt通過乙二醇還原H2PtCl6沉積到Co納米顆粒上，以XC-72活性碳負(fù)載PtCo納米顆粒制成PtCo/C催化劑。非原位數(shù)據(jù)采集使用沒有經(jīng)過活化處理的PtCo/C粉末，但是制備成膜電極組件和組裝成燃料電池后，在采集燃料電池的原位XAFS數(shù)據(jù)前，需要經(jīng)過24 h的活化（100%氫氣，反應(yīng)溫度為70 oC）處理，活化處理過程是在燃料電池里完成。

1.1.2 膜電極組件(Membrane Electrode Accemblies, MEA)的制備

取0.04 g的PtCo/C催化劑，并加入0.72 mL H2O, 0.372 g的5% Nafion溶液（美國杜邦公司），1.5 g異丙醇，超聲分散3 h，然后把Nafion 212膜（美國杜邦公司）在加熱平臺上加熱至80 oC，把經(jīng)過超聲分散后的溶液噴涂在Nafion膜上，催化劑噴涂面積為20 mm′20 mm。取Pd/C (10 wt%，莊信萬豐公司(Johnson Matthey company)) 0.08 g，加入1.44 mL H2O，0.744 g 5% Nafion溶液，3.0 g異丙醇，同樣超聲分散3 h后，在80 oC下噴到Nafion 212膜的另一面。將噴好的Nafion膜置于已裁剪的大小和催化劑面積完全相同的炭紙中間，然后在150 oC和5MPa下熱壓制備成PtCo/C-Pd/C膜電極組件，同樣的方法制備一面是Pt/C (20 wt%，Johnson Matthey company)，另一面是Pd/C (10 wt%，Johnson Matthey company)的JM-Pt/C- Pd/C膜電極組件。

1.2 PtCo/C的結(jié)構(gòu)表征

使用電感耦合等離子體質(zhì)譜(Inductively coupled plasma mass spectrometry, ICP-MS)測定PtCo/C的組分和原子比，所用儀器型號為美國熱電公司生產(chǎn)的Thermo Elemental XZ-ICP-MS X0186，取兩個平行樣的平均值。

用來測定催化劑的比表面積，所用儀器為美國Micromeritics公司生產(chǎn)的ASAP2020。采用液氮作為吸附質(zhì)。

化學(xué)吸附法用來測定活性金屬表面積和金屬分散度，所用儀器為美國Micromeritics公司生產(chǎn)的AutoChem HP 2950。采用脈沖化學(xué)吸附法，以一定劑量的CO（一個脈沖）在相同的時間間隔內(nèi)注入催化劑表面，直到檢測出來的信號峰強(qiáng)度穩(wěn)定為止。用每一脈沖對應(yīng)的峰面積乘以總脈沖數(shù)，減去檢測到的峰面積即為吸收的氣體對應(yīng)的峰面積。

式中：表示金屬分散度；ad表示吸附的體積；表示氣體分子量；metal%表示金屬的質(zhì)量分?jǐn)?shù)；表示所用催化劑的質(zhì)量；表示金屬表面積；0=6.02′1023；為金屬原子截面積。

TEM的型號為美國FEI公司生產(chǎn)的Tecnai G2 F20S-TWIN場發(fā)射透射電子顯微鏡(Field Emission Transmission Electron Microscope)。

采用德國Bruker公司生產(chǎn)的D8 Advance X射線衍射儀，對PtCo/C粉末進(jìn)行XRD測試，X射線管電壓為40 kV，管電流為40 mA，步長o，掃描范圍(2)為o，積分時間1 s。

在上海光源BL14W1線站采集PtCo/C粉末的非原位XAFS譜，Pt采用透射模式采集XAFS譜，Co采用熒光模式采集XAFS譜。BL14W1線站使用Si(111)雙晶單色器來選擇X光能量，對于Pt L3邊的測量，前電離室氣體為90% N2和10% Ar，后電離室氣體為75% N2和25% Ar，Co K邊的測量，前后電離室氣體均為75% N2和25% He。

1.3 PtCo/C原位XAFS譜的采集

1.3.1 原位XAFS燃料電池催化劑實驗裝置

在上海光源BL14W1線站搭建的原位燃料電池實驗裝置，如圖1、2所示。整套裝置主要由原位樣品池、加熱、加濕、氣體控制、電化學(xué)信號采集幾個模塊組成，其中樣品池位于電離室和固體探測器之間。

1.3.2實驗條件

兩張MEA（PtCo/C-Pd/C和JM-Pt/C-Pd/C）在采集原位數(shù)據(jù)前，都經(jīng)過了24 h的活化，反應(yīng)溫度為70 oC，氫氣（20%的氫氦混合氣）流量125mL?min?1，空氣流量50 mL?min?1，氫氣和空氣在進(jìn)入燃料電池反應(yīng)前都經(jīng)過加濕罐進(jìn)行加濕。PtCo/C樣品的原位XAFS數(shù)據(jù)采集采用熒光模式，使用32元高純Ge固體探測器采集PtCo/C的原位XAFS譜，每個數(shù)據(jù)點的積分時間都為3 s，通過電化學(xué)工作站調(diào)節(jié)工作電壓變化，分別采集不同電壓下Pt和Co的原位XAFS譜圖。

圖1 上海光源BL14W1線站的原位燃料電池實驗裝置示意圖Fig.1 Schematic drawing of thein situ XAFS experiment instrument for fuel cell on beamline BL14W1Shanghai Synchrotron Radiation Facility (SSRF).

圖2 上海光源BL14W1線站的原位燃料電池實驗裝置Fig.2 Picture of thein situXAFS experiment instrument for fuel cell on beamline BL14W1 at SSRF.

2 結(jié)果與分析

2.1 PtCo/C和JM-Pt/C的物理參數(shù)比較

ICP實驗結(jié)果顯示Pt 的質(zhì)量百分比為10.3%，Co的質(zhì)量百分比為0.18%，Pt與Co的原子數(shù)比為17:1。如表1所示，的Pt的質(zhì)量百分比僅為商業(yè)催化劑JM-Pt/C的50%，PtCo/C催化劑粒徑更小，但是比表面積小于JM-Pt/C。

表1 PtCo/C和JM-Pt/C物理參數(shù)比較
Table 1 Physical parameters PtCo/C and JM-Pt/C comparison.

Pt的質(zhì)量百分比

Pt / wt%

平均粒徑

Averaged grain

size / nm

比表面積

Specific surface area

(BET) / m?g

金屬表面積

Metal surface area

(CO chemistry) / m?g

金屬分散度

Metal atom

dispersed / %

PtCo/C

10.3

2.8

96

76

10

JM-Pt/C

20.0

3.5

125

90

28

2.2 PtCo/C與JM-Pt/C的TEM數(shù)據(jù)分析

分別采集PtCo/C和JM-Pt/C的TEM成像和高分辨透射電鏡(High Resolution TEM, HRTEM)成像，如圖3所示，PtCo/C和JM-Pt/C的粒徑分布都比較均勻。使用粒度分析軟件Nano Measurer 1.2.5對PtCo/C和JM-Pt/C的納米顆粒尺寸進(jìn)行統(tǒng)計分析，PtCo/C平均粒徑2.8 nm，小于JM-Pt/C的3.5nm，更小納米尺寸有利于提高PtCo/C催化ORR的活性。

圖3 PtCo/C (a)和JM-Pt/C (d)的TEM圖，PtCo/C (b)和JM-Pt/C (e)的HRTEM圖，PtCo/C (c)和JM-Pt/C (f)的粒徑分布圖Fig.3 TEM images of PtCo/C (a) and JM-Pt/C (d), HRTEM images of PtCo/C (b) and JM-Pt/C (e), and distribution of nanoparticle size distributions from analysis of TEM images of PtCo/C (c) and JM-Pt/C (f).

2.3 PtCo/C與JM-Pt/C的XRD數(shù)據(jù)分析

與JM-Pt/C的XRD數(shù)據(jù)如圖4所示。JM-Pt/C的衍射峰出現(xiàn)在39.8o、46.3o、67.5o、81.3o，分別對應(yīng)Pt的(111)、(200)、(220)、(311)晶面，表示Pt的面心立方晶格結(jié)構(gòu)[30]，PtCo/C的衍射峰相比JM-Pt/C寬化，表明PtCo/C具有更小的納米顆粒尺寸[31]。PtCo/C與JM-Pt/C的TEM數(shù)據(jù)證實了這一點。

圖4 PtCo/C和JM-Pt/C的XRD數(shù)據(jù)
Fig.4 XRD patterns of the PtCo/C and JM-Pt/C.

2.4 PtCo/C與JM-Pt/C的非原位擴(kuò)展邊X射線吸收精細(xì)結(jié)構(gòu)數(shù)據(jù)分析

軟件包對實驗獲得的EXAFS數(shù)據(jù)進(jìn)行處理，結(jié)果如表2所示。5是PtCo/C與JM-Pt/C的空間變換，圖6是PtCo/C和JM-Pt/C的EXAFS擬合后的空間變換。此時由于PtCo/C的粉末未經(jīng)還原處理，由PtCo/C的粉末EXAFS的擬合結(jié)果可知，Pt與Co并沒有成鍵，存在顯著的Co?O和Co?O?Co相互作用，說明PtCo/C中的Co主要以氧化物的形式存在。與JM-Pt/C相比，PtCo/C中Pt的氧化程度更高且具有更短的Pt?Pt金屬鍵長，說明Co的存在影響著催化劑的活性成分Pt的氧化程度，Pt?Pt鍵長的縮短有可能來自Co的影響和尺寸效應(yīng)。

圖5 PtCo/C和JM-Pt/C的空間變換
Fig.53-weighted EXAFS oscillations() at Pt L3-edge and their Fourier transforms for PtCo/C and JM-Pt/C.

圖6 PtCo/C和JM-Pt/C的EXAFS擬合結(jié)果(a) PtCo/C的Pt的L3擬合結(jié)果，(b) PtCo/C的Co的K邊擬合結(jié)果，(c) JM-Pt/C的Pt的L3邊擬合結(jié)果Fig.6 Data and ?ts of the magnitude of Fourier transformedk2-weighted EXAFS spectra of PtCo/C and JM-Pt/C catalysts.(a) PtCo/C of the Pt L3edge, (b) PtCo/C of the Co K edge, (c) JM-Pt/C of the Pt L3edge

表2 PtCo/C和JM-Pt/C的EXAFS擬合結(jié)果
Table 2 Structural and electronic structural parameters obtained by EXAFS analysis for PtCo/C and JM-Pt/C catalysts.

樣品

Sample

殼層

Shell

配位數(shù)

Coordination numbers

鍵長

Bond length / ?

/10?

能量原點的位移

Δ/ eV

PtCo/C

Pt?O

2.6±0.3

2.01±0.02

5.9±1.6

9.9±0.8

Pt?Pt

3.5±1.4

2.69±0.02

9.6±3.0

7.5±0.5

Co?O

4.3±0.7

1.90±0.01

4.8±2.3

?7.2±1.6

Co?O?Co

3.7±1.1

2.80±0.02

5.6±2.8

?3.4±0.7

JM-Pt/C

Pt?O

2.5±0.3

2.01±0.02

3.8±1.5

9.9±0.8

Pt?Pt

5.1±0.9

2.75±0.02

6.4±1.0

7.5±0.5

2.5 PtCo/C和JM-Pt/C的原位近邊X射線吸收精細(xì)結(jié)構(gòu)譜分析

如圖7所示，PtCo/C經(jīng)過24 h的活化處理之后，隨著電壓逐漸減小，電流密度逐漸增大，PtCo/C和JM-Pt/C中Pt的氧化程度逐漸降低，XANES的線性擬合結(jié)果如圖8所示，JM-Pt/C在低電位時出現(xiàn)PtO2含量略有升高。如圖9所示，Co的線性擬合顯示，Co的原位XANES是Co和CoO的混合物，在催化反應(yīng)過程中，隨著電壓逐漸減小，Co的氧化程度也隨之逐漸降低，揭示了在催化反應(yīng)過程中Pt的d電子向過渡金屬Co的轉(zhuǎn)移過程，從而導(dǎo)致Pt的d帶空位的增加。這說明Co的存在可以影響Pt的外層電子結(jié)構(gòu)，由于尺寸效應(yīng)和Co的影響使PtCo/C催化劑具有更短的Pt?Pt鍵長，從而增強(qiáng)Pt的催化ORR的活性。在低電位時，Co的存在可以抑制PtO2含量的增加，而反應(yīng)過程中Pt?O鍵的存在能抑制Pt的催化反應(yīng)活性[27]。

圖7 PtCo/C (a)和JM-Pt/C (b) Pt的原位XANES譜比較Fig.7 In situXANES spectra collected at Pt L3edge of PtCo/C (a) and JM-Pt/C (b) catalystwith different potentials comparison during the operation of fuel cell.

圖8 PtCo/C (a)和JM-Pt/C (b)催化劑Pt的原位XANES譜數(shù)據(jù)的線性擬合結(jié)果比較Fig.8 Linear fitting results ofin situXANES spectra of PtCo/C (a) and JM-Pt/C (b) catalyst comparison.

圖9 PtCo/C催化劑Co的原位XANES譜Fig.9 In situXANES spectra collected at Co K edge of PtCo/C with different potentials duringthe operation of fuel cell.

2.6 PtCo/C和JM-Pt/C在工作條件下的功率密度曲線分析

如圖10所示，PtCo/C和JM-Pt/C催化劑從開路電壓(Open circuit voltage, OCV)開始，隨著電壓的逐漸減小，電流密度的逐漸增大，功率密度也隨之增大，當(dāng)電壓降到0.4 V左右時，燃料電池的功率密度達(dá)到極大值。從JM-Pt/C和PtCo/C的功率曲線可以看出，PtCo/C的催化性能非常接近商業(yè)Pt/C催化劑，但是與JM-Pt/C相比，PtCo/C減少了50%的Pt的使用量，因此具有更好的商業(yè)應(yīng)用前景。

圖10 PtCo/C和JM-Pt/C催化劑在工作狀態(tài)下的性能曲線比較Fig.10 Performance curve of PtCo/C and JM-Pt/C catalyst comparison in fue cell working condition.

3 結(jié)語

在Pt中摻雜過渡金屬元素Co形成的PtCo/C納米催化劑，與商業(yè)Pt/C催化劑相比，由于Co的存在能夠影響Pt的氧化程度，使得金屬Pt晶格變小，Pt?Pt鍵長縮短，導(dǎo)致PtCo/C具有更小的納米尺寸，減小了Pt?Pt 鍵之間的距離，從而提高PtCo/C納米催化劑中Pt的催化活性。過渡金屬Co有比Pt更多的d帶空位，原位XAFS實驗揭示了PtCo/C在催化反應(yīng)過程中Pt的d電子向過渡金屬Co的轉(zhuǎn)移過程，Pt的d帶空位的增加，有利于提高Pt催化ORR反應(yīng)的性能。

. Catalysis Reviews-Science and Engineering, 2001, 43(1?2): 31?84. DOI: 10.1081/CR-100104386

. Platinum Metals Review, 2002, 46(3): 117?135

Fuel Cells, 2005, 5(2): 187?200. DOI: 10.1002/ fuce.200400045

Journal of Power Sources, 2008, 180(1): 1?14. DOI: 10.1016/j.jpowsour.2008.01. 070

5 Borup R, Meyers J, Pivovar B,. Scientific aspects of polymer electrolyte fuel cell durability and degradation[J]. Chemical Reviews, 2007, 107(10): 3904?3951. DOI: 10.1021/cr050182l

. Journal of Power Sources, 2006, 155(2): 253?263. DOI: 10.1016/j.jpowsour. 2005.05.011

[J]. Fuel Cells, 2001, 1(1): 5?39. DOI: 10.1002/1615-6854(200105)1:1<5:: AID- FUCE5>3.0.CO;2-G

. Ni@Pt core–shell nanoparticles with enhanced catalytic activity for oxygen reduction reaction. Journal of Alloys and Compounds, 2010, 503(1): L1?L4. DOI: 10.1016/j.jallcom.2010.04. 236

9 Laetitia D, Tristan A, Raphael C,. Tuning the performance and the stability of porous hollow PtNi/C nanostructures for the oxygen reduction reactionAmerican Chemical Society Catalysis, 2015, 5(9): 5333?5341. DOI: 10.1021/acscatal.5b01248

. Origin of the enhanced electrocatalysis for thermally controlled nanostructure of bimetallic nanoparticles[J]., 2014, 118(19): 9939?9945. DOI: 10.1021/jp5019982

.Multimetallic core/interlayer/shell nanostructures as advanced electrocatalysts[J]. Nano Letters, 2014, 14(11): 6361?6367. DOI: 10.1021/nl5028205

12 Duan H M, Hao Q, Xu C X. Nanoporous PtFe alloys as highly active and durable electrocatalysts for oxygen reduction reaction[J]. Journal of Power Sources, 2014, 269: 589?596. DOI: 10.1016/j.jpowsour.2014.07. 026

.study of atomic structure transformations of Pt-Ni nanoparticle catalysts during electrochemical potential cycling[J]. American Chemical Society Nano, 2013, 7(7): 5666?5674. DOI: 10.1021/nn402406k

14 Kristian N, Yua Y, Lee J M,.Synthesis and characterization of Cocore–Ptshellelectrocatalyst prepared by spontaneous replacement reaction for oxygen reduction reaction[J]. Electrochimica Acta, 2010, 56(2):1000?1007. DOI: 10.1016/j.electacta.2010.09.073

15 Lin R, Cao C H, Zhao T T,. Synthesis and application of coreeshell Co@Pt/C electrocatalysts for proton exchange membrane fuel cells[J]. Journal of Power Sources, 2013, 223: 190?198. DOI: 10.1016/ j.jpowsour.2012.09.073

. DOI: 10.1016/j.electacta.2013. 04.060

20 Jia Q Y, Liang W T, Bates M K,. Activity descriptor identi?cation for oxygen reduction on platinum-based bimetallic nanoparticles:observation of the linear composition-strain-activity relationship[J]. American Chemical Society Nano, 2015, 9(1): 387?400. DOI: 10.1021/nn506721f

21 Loukrakpam R, Luo J, He T,.Nanoengineered PtCo and PtNi catalysts for oxygen reduction reaction: an assessment of the structural and electrocatalytic properties[J]. The Journal of Physical Chemistry C, 2011, 115(5): 1682?1694. DOI: 10.1021/jp109630n

22 Patrick B, Ham H C, Yang S H,. Atomic structure and composition of “PtCo” nanocatalysts in fuel cells: an aberration-corrected STEM HAADF study[J]. Chemistry of Materials, 2013, 25(4): 530–535. DOI: 10.1021/cm3029164

.Carbon-supported Pt-based alloy electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells: particle size, shape, and composition manipulation and their impact to activity. American Chemical Society Chemical Reviews, 2015, 115(9): 3433?3467. DOI: 10.1021/cr500519c

24 Spanos I, Kirkensgaard J J K, Mortensen K,.Investigating the activity enhancement on PtCo1?xalloys induced by a combined strain and ligand effect[J]. Journal of Power Sources, 2014, 245: 908?914. DOI: 10.1016/ j.jpowsour.2013.07.023

25 Shirlaine K, Jennifer L, Michael F,.Structure-activity-stability relationships of Pt-Co alloy electrocatalysts in gas-diffusion electrode layers.The Journal of Physical Chemistry C, 2007, 111(9): 3744?3752. DOI: 10.1021/jp067269a

26 Ishiguro N, Kityakarn S, Tada M,. Rate enhancements in structural transformations of Pt?Co and PtNi bimetallic cathode catalysts in polymer electrolyte fuel cells studied bytime-resolved X-ray absorption fine structure[J]. The Journal of PhysicalChemistry C, 2014, 118(29): 15874?15883. DOI: 10.1021/jp504738p

27 Nagamatsu S, Arai T, Iwasawa Y,.Potential- dependent restructuring and hysteresis in the structural and electronic transformations of Pt/C, Au(Core)- Pt(Shell)/C, and Pd(Core)-Pt(Shell)/C cathode catalysts in polymer electrolyte fuel cells characterized by in situ X-ray absorption fine structure[J]. The Journal of Physical Chemistry C, 2013, 117(25): 13094?13107. DOI: 10.1021/jp402438e

Witkowska A, Cicco A D,. Local ordering changes in Pt?Co nanocatalyst induced by fuel cell working conditions[J]. The Journal of Physical Chemistry C, 2012, 116(23): 12791?12802. DOI: 10.1021/jp2099569

黃宇營, 王建強(qiáng), 等.實驗方法[J]. 物理化學(xué)學(xué)報, 2015, 31(8): 1609?1614. DOI: 10.3866/PKU. WHXB201505252
SHANG Mingfeng, HUANG Yuying, WANG Jianqiang,.XAFS experimental methods for catalyst structure of proton exchange membrane fuel cell[J]. Acta Physico-Chimica Sinica, 2015, 31(8): 1609?1614. DOI: 10.3866/PKU.WHXB201505252

30 Lee M H, Do J S. Kinetics of oxygen reduction reaction on Co-Pt/C electrocatalysts[J].Journal of Power Sources, 2009, 188(2): 353?358. DOI: 10.1016/ j.jpowsour.2008.12.051

31 Xion L, Kanna A M, Manthiram A. Pt-M (M=Fe,Co,Ni, and Cu) electrocatalysts synthesized by an aqueous route for proton exchange membrane fuel cells[J]. Electrochemistry Communication, 2002, 4(11): 898?903. DOI: 10.1016/S1388-2481(02)00485-X

國家重點基礎(chǔ)研究發(fā)展計劃(973計劃)(No.2013CB933104)、(No.91127001、No.11079005)資助

Supported by the Major Project of Chinese National Programs for Fundamental Research and Development (973 Program)(No.2013CB933104), National Natural Science Foundation of China (No.91127001, No.11079005)

XAFS characterization of bimetallic nanoparticle catalysts PtCo/C structure changes in the working conditions

SHANG Mingfeng1ZHAO Tiantian2BAO Hongliang1DUAN Peiquan1LIN Rui2HUANG Yuying1WANG Jianqiang1

1(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Zhangjiang Campus, Shanghai 201204, China)2(School of Automotive Studies, Tongji University, Shanghai 201804, China)

Background: The proton exchange membrane fuel cell (PEMFC) is considered as one of the most promising clean energy sources in the future, because of its high energy density and simple construction. However, the large scale commercial application of fuel cell is limited by the factors such as cost, durability and reliability. Purpose: For the purpose of reducing the cost and improving the performance of the PEMFC, transition metal elements alloy Pt nanoparticles (PtFe/C, PtCo/C, PtNi/C) catalysts have been studied in recent years. Methods:experimental testing device for PEMFC on beamline (BL14W1) of XAFS spectroscopy at the Shanghai Synchrotron Radiation Facility (SSRF) is conducted to explore thenanostructure changes of PtCo/C during the fuel cell operation. Results:XAFS spectra indicts that Pt, and Co are gradually being reduced as the voltage of fuel cell decreases.XAFS spectra show Pt and Co did not form Pt?Co bond, but there is a strong Co?O bond and Co?O?Co bond. Conclusion: The element of Co improves the performance of PtCo/C catalysts for the oxygen reduction reaction (ORR) and decreases the cost of fuel cells by regulating the electronic structure of Pt.

PEMFC,, XAFS, Nanostructure changes

SHANG Mingfeng, male, born in 1982, graduated from Nanjing Normal University in 2007, doctor student, major in inorganic chemistry

HUANG Yuying, E-mail: huangyuying@sinap.ac.cn; WANG Jianqiang, E-mail: wangjianqiang@sinap.ac.cn

TL99

10.11889/j.0253-3219.2016.hjs.39.060101

尚明豐，男，1982年出生，2007年畢業(yè)于南京師范大學(xué)，現(xiàn)為博士研究生，

黃宇營，E-mail: huangyuying@sinap.ac.cn；王建強(qiáng)，E-mail: wangjianqiang@sinap.ac.cn

2016-03-30，

2016-04-13