Effect of Pt supported on the hybrid of porous carbon nanofibers and carbon black on oxygen reduction reaction activity and durability
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摘要:
进一步提高Pt催化剂对氧还原反应(ORR)的催化活性和稳定性是促进质子交换膜燃料电池(PEMFC)商业化的关键。采用静电纺丝结合高温碳化的方法制备了直径约200 nm的多孔纳米碳纤维(PCNF)，将其与炭黑(CB)混合作为Pt催化剂的复合载体，并使用乙二醇还原法制备了催化剂Pt/PCNF-CB，通过与商业Pt/C催化剂的对比，研究了Pt/PCNF-CB对ORR的催化活性与稳定性。当载体中CB含量为40wt%时，PCNF与CB能相互分散均匀，构建独特的三维贯通结构，以此混合载体制备的催化剂Pt/PCNF-CB-40在酸性电解液中表现出优良的ORR电催化活性，与Pt/C相比具有更高的起始电位(0.975 V)与半波电位(0.781 V)。同时，基于Pt/PCNF-CB-40的膜电极(MEA)表现出优良的输出性能，在铂载量较低的条件下其峰值功率密度高达599 mW·cm−2，较商业Pt/C催化剂提升19%，并且在加速应力测试(AST) (0.6 V和0.95 V)
30000 次循环后最大功率密度仅损失21%，而商业Pt/C催化剂损失了41%，证明了PCNF与CB形成的复合载体对提高催化剂活性和稳定性具有积极作用。Abstract:Further improving the activity and stability of Pt catalysts for oxygen reduction reaction (ORR) is the key to promote the commercialization of proton exchange membrane fuel cells (PEMFCs). In this paper, porous carbon nanofibers (PCNF) with a diameter of about 200 nm were prepared by electrospinning and followed carbonization, which were mixed with carbon black (CB) as a hybrid support for Pt catalysts, and the catalysts Pt/PCNF-CB were prepared by means of ethylene glycol reduction method. The electrocatalytic activity and stability of Pt/PCNF-CB for ORR was investigated by comparing it with commercial Pt/C. When the CB content in the support was 40wt%, PCNF and CB could disperse uniformly to construct a unique three-dimensional through structure, and the Pt/PCNF-CB-40 prepared from this hybrid support shows excellent ORR electrocatalytic activity in acidic electrolyte with higher onset potential (0.975 V) and half-wave potential (0.781 V) compared with commercial Pt/C. Meanwhile, the Pt/PCNF-CB-40-based membrane electrode assembly (MEA) exhibits higher output performance with a peak power density of up to 599 mW·cm−2 at low Pt loading, which is a 19% improvement over the commercial Pt/C, and the maximum power density is only lost by 21% after
30000 of accelerated stress test (AST) (0.6 V and 0.95 V), compared with the loss of the commercial Pt/C by 41%, demonstrating that the hybrid support formed by PCNF and CB has a positive effect on improving electrocatalytic activity and stability. -
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图 1 多孔纳米碳纤维(PCNF)制备工艺示意图(a)与PCNF的SEM图像：(b)断面；(c)表面
Figure 1. Process schematic of porous carbon nanofibers (PCNF) (a) and SEM images of PCNF: (b) Cross section; (c) Surface
PAN—Polyacrylonitrile; PMMA—Polymethyl methacrylate
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图 2 催化剂的SEM图像：Pt/PCNF (a)，Pt/PCNF-CB-30 (b)，Pt/PCNF-CB-40 (c)，Pt/PCNF-CB-50 (d)；催化剂的TEM图像：Pt/PCNF (e)，Pt/PCNF-CB-30 (f)，Pt/PCNF-CB-40 (g)，Pt/PCNF-CB-50 (h)
Figure 2. SEM images of electrocatalysts: Pt/PCNF (a), Pt/PCNF-CB-30 (b), Pt/PCNF-CB-40 (c), Pt/PCNF-CB-50 (d); TEM images of electrocatalysts: Pt/PCNF (e), Pt/PCNF-CB-30 (f), Pt/PCNF-CB-40 (g), Pt/PCNF-CB-50 (h)
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图 4 Pt/PCNF-CB的TEM图像
Figure 4. TEM images of Pt/PCNF-CB electrocatalysts
d—Interplanar spacing
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图 5 商业Pt/C与Pt/PCNF-CB在0.5 mol·L−1 H2SO4中的CV曲线(扫描速率为50 mV·s−1) (a)、LSV曲线(扫速为
1600 r/min) (b)与Tafel斜率(c)Figure 5. CV curves of commercial Pt/C and Pt/PCNF-CB series electrocatalysts in 0.5 mol·L−1 H2SO4 (under the scanning rate of 50 mV·s−1) (a), LSV curves of commercial Pt/C and Pt/PCNF-CB series electrocatalysts (under the
1600 r/min electrode rotation speed) (b) and Tafel plots (c)RHE—Reversible hydrogen electrode; j—Absolute value of current density
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图 6 商业Pt/C和Pt/PCNF-CB-40催化剂
2000 圈循环老化前后的CV与LSV曲线Figure 6. CV and LSV curves of commercial Pt/C and Pt/PCNF-CB-40 electrocatalysts before and after
2000 potential sweeps∆E1/2—Half-wave potential change value
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图 7 Pt/PCNF-CB-40 (a)和商用Pt/C (b)催化剂
2000 圈循环老化后的TEM图像Figure 7. TEM images of Pt/PCNF-CB-40 (a) and commercial Pt/C (b) electrocatalysts after
2000 potential sweep![]()
图 8 Pt/PCNF-CB-40与Pt/C分别作为阴极的膜电极(MEA)在H2/Air中的极化曲线与功率密度曲线(a)以及Pt/PCNF-CB-40与Pt/C在0.4 A·cm−2下的电化学阻抗谱(EIS)曲线(b)
Figure 8. Polarization and power density curves (a) and electrochemical impedance spectroscopy (EIS) curves (b) of membrane electrode assembly (MEA) of Pt/PCNF-CB-40 and Pt/C as cathodes respectively in H2/Air at 0.4 A·cm−2
Z'—The real part of impedance; Z''—The imaginary part of impedance; R1, R2, R3—Battery impedance; CPE1, CPE2—Constant phase element
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图 9 自制催化剂Pt/PCNF-CB-40与商业Pt/C制备的MEA在加速应力测试(AST)前后的极化曲线和功率密度曲线
Figure 9. Polarization and power density curves of MEA prepared by homemade electrocatalyst Pt/PCNF-CB-40 and commercial Pt/C before and after accelerated stress test (AST)
表 1 各催化剂的组成
Table 1 Composition of catalysts
Catalyst Composition of the support Pt loading/wt% Pt/PCNF PCNF 20±1.5 Pt/PCNF-CB-30 PCNF∶CB=7∶3 Pt/PCNF-CB-40 PCNF∶CB=6∶4 Pt/PCNF-CB-50 PCNF∶CB=5∶5 Notes: PCNF—Porous carbon nanofibers; CB—Carbon black. 
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表 2 以Pt/PCNF-CB-40与Pt/C制备的膜电极(MEA)电化学性能对比
Table 2 Comparison of electrochemical properties of membrane electrode assembly (MEA) prepared with Pt/PCNF-CB-40 and Pt/C
Sample Maximum power density/(mW·cm−2) R0/(mΩ·cm−2) Rct/(mΩ·cm−2) Rmt/(mΩ·cm−2) Pt/PCNF-CB-40 599 0.934 4.078 6.565 Pt/C 502 1.815 10.632 8.005 Notes：R0 is the internal resistance of cell including the resistance of each component in cells and their interfaces; Rct is the charge transfer resistance; Rmt is the mass transport resistance.
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其他类型引用(24)
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其他相关附件
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目的
进一步提高Pt催化剂对氧还原反应(ORR)的催化活性和稳定性是促进质子交换膜燃料电池(PEMFC)商业化的关键。本文采用制备了直径约200 nm的多孔纳米碳纤维(PCNF)，将其与炭黑(CB)混合作为Pt催化剂的复合载体制备了催化剂Pt/PCNF-CB，通过与商业Pt/C催化剂的对比，研究了Pt/PCNF-CB对ORR的催化活性与稳定性。
方法采用静电纺丝结合1000 ℃下高温碳化制备了直径约200 nm的PCNF。将PCNF与CB作为复合载体，以氯铂酸作为前驱体使用乙二醇还原法制备了催化剂Pt/PCNF-CB。利用场发射扫描电镜(SEM)研究了PCNF与CB复合载体的形貌，采用透射电子显微镜(TEM)检测了Pt纳米颗粒在纤维上的分散性与粒径大小。在旋转圆盘电极使用线性扫描伏安法(LSV)与循环伏安法(CV)完成催化剂的电化学表征，并通过加速老化测试(ADT)比较了催化剂的活性与耐久性。采用催化剂涂覆膜法制备阳极和阴极催化剂层，使用了热压机热压以获得膜电极(MEA)并使用燃料电池测试系统获得了MEA的极化曲线与功率密度曲线。膜电极(MEA)稳定性测试使用了0.6 V和0.95 V的方波电压循环，对比催化剂在5 k，10 k，30 k次循环后的最大功率密度衰减程度。
结果①当载体中CB含量40%时，PCNF和CB之间分散性更佳。根据催化剂形貌的TEM图像，可以看到Pt颗粒成功负载于复合载体上。其中负载于PCNF表面的Pt纳米粒子更加均匀，体现了多孔粗糙的PCNF表面对提高Pt颗粒分散性的积极作用。②催化剂Pt/PCNF-CB-40比商业的Pt/C具有更高的催化活性和稳定性，从得到的CV曲线计算得出Pt/PCNF-CB-40的氢脱附峰面积最大为86.3 m·g，高于商业Pt/C(71.7 m·g)，而LSV曲线中Pt/PCNF-CB-40表现出更高的起始电位(0.975 V)与半波电位(0.781 V)。并且在2000次ADT后，Pt/PCNF-CB-40的性能衰减幅度小于商业Pt/C，半波电位下降了23 mV小于商业Pt/C(60 mV)。③由Pt/PCNF-CB-40组装的MEA比由Pt/C组装的MEA表现出更高的最大功率密度(599 mW·cm)，较商业Pt/C催化剂提升19%，并在5 k，10 k与30 k次低电位循环后Pt/PCNF-CB-40的最大功率密度仅衰减了10%，17%以及21%，远低于商业Pt/C的22%，25%与41%的损耗。
结论Pt/PCNF-CB利用了两种载体不同的形貌特征，使PCNF与CB相互分散搭建了三维贯通的多孔结构，能提供更多三相反应界面，并减少传质阻力，以此混合载体制备的催化剂Pt/PCNF-CB-40在酸性电解液中表现出优良的ORR电催化活性，并在MEA测试中作为阴极催化剂表现了更高的输出性能。由于PCNF的粗糙多孔结构有利于Pt纳米粒子的均匀分散，在运行过程中由于复合载体中PCNF上丰富的缺陷位点与Pt粒子之间的强结合能有效抑制了Pt粒子的迁移，防止其从载体脱落与聚集提高了催化剂的耐久性，使Pt/PCNF-CB在三电极体系与燃料电池测试系统中均表现出了更佳的耐久性。PCNF与CB的协同作用提高了催化剂的活性与耐久性。
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质子交换膜燃料电池(PEMFC)是一种通过电化学反应将化学能转换为电能的能源转换装置，具有功率密度高、结构简单、环境友好等优点。然而，PEMFC阴极氧还原反应(ORR)缓慢的动力学与高的过电位都需要依靠贵金属Pt基催化剂以加快反应，但Pt的高成本以及商业Pt/C的耐久性差制约了其商业化发展。
本文采用静电纺丝结合预氧化和碳化制备了多孔纳米碳纤维(PCNF)，将其与炭黑(CB)混合作为复合载体负载Pt制备了催化剂Pt/PCNF-CB。PCNF的粗糙多孔结构不但有利于Pt纳米粒子的均匀分散，也增强了Pt纳米粒子与载体间的相互作用，使载体能够牢固地锚定Pt纳米粒子。此外，利用两种载体不同的形貌特征，PCNF与CB相互分散搭建了三维贯通的多孔结构，能提供更多三相反应界面，并减少传质阻力。正是两者的协同作用提高了催化剂的活性与耐久性。在低铂负载量下(阴、阳极负载量分别为0.15 mgPt·cm-2和0.1 mgPt·cm-2)，由自制催化剂组装的膜电极最高输出功率密度可达599 mW·cm-2，高于商业Pt/C(502 mW·cm-2)，尤其在低电位循环30 k圈后最大输出功率仅衰减21%，而相同条件下商业Pt/C衰减41%。
自制催化剂Pt/PCNF-CB-40与商业Pt/C组装的膜电极加速老化测试的极化曲线和功率密度曲线
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