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摘要: 以Vulcan XC-72炭为载体,采用硼氢化钠还原法制备了Pd-TiO2/C电催化剂用于直接丙三醇燃料电池阳极材料,并用能量色散谱(EDX)、X射线衍射(XRD)、透射电子显微镜(TEM)、循环伏安法(CV)、计时电流法(I-t)和全反射-傅里叶变换红外光谱(ATR-FTIR)对催化剂进行了表征。EDX结果表明,Pd-TiO2/C中Pd和Ti含量接近名义原子比。Pd-TiO2的X射线衍射结果表明,Pd具有面心立方fcc结构,同时TiO2展现出四方结构的锐钛矿相的峰特征。TEM图像显示Pd和TiO2纳米颗粒在碳载体中分布均匀并存在一些簇状区域,纳米颗粒大小为7.0 − 8.0 nm。循环伏安显示在1 mol/L KOH电解液中催化剂Pd-TiO2/C在 约 −0.7 V vs Ag/AgCl有明显的析氢行为和电容增加现象,表明催化剂在TiO2修饰后活性明显增加。通过循环伏安对碱性体系的丙三醇电催化氧化表明,Pd-TiO2/C(70∶30)显示了非常好的催化活性:起始氧化电位也变得更负达到−0.4V vs Ag/AgCl,氧化电流达到14.91 mA/cm,优于Pd-TiO2/C(90∶10)的9.37 mA/cm和Pd-TiO2/C(50∶50) 的4.88 mA/cm,明显高于Pd/C和TiO2/C的1.88 和0.55 mA/cm。I-t实验表明1000 s之前Pd-TiO2/C展现出最高的电流密度,但在1000 s后电流密度有一定程度的下降,表明催化剂的催化活性很高但长期稳定性方面需要进一步提升。在碱性直接丙三醇燃料电池中进行的实验表明,所制备的Pd-TiO2/C(50∶50)、Pd-TiO2/C(70∶30)和Pd-TiO2/C(90∶10)对甘油的电化学氧化性能均优于Pd/C电催化剂,其中,Pd-TiO2/C(70∶30)的催化活性最好:开路电压达到817 mV,最大功率密度达到12.5 mW/cm,高于Pd-TiO2/C(50∶50)的12.4 mW/cm、Pd-TiO2/C(90∶10)的7.9 mW/cm、Pd/C的3.7 mW/cm以及 TiO2/C的2.25 mW/cm,这表明,TiO2对Pd/C催化剂有很好的促进作用,这种协同效应可以归因为TiO2对Pd的电子效应和双功能机理,同时Pd和TiO2比例为70∶30时,其催化性能达到最优。ATR-FTIR结果表明,反应后所有Pd-TiO2/C电催化剂表面均有甘油醛、羟丙酮酸、甲酸等高附加值产物生成,为直接丙三醇燃料电池电-化学品联产提供一定的依据。
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关键词:
- 丙三醇氧化 /
- Pd-TiO2 电催化剂 /
- 原位ATR-FTIR /
- 循环伏安 /
- 碱性燃料电池
Abstract: The Pd-TiO2 electrocatalysts were synthesized via sodium borohydride reduction and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry, chronoamperometry and attenuated total reflectance-Fourier transform infrared (ATR-FTIR). The X-ray diffraction experiments of the Pd-TiO2 showed peaks associated with Pd face-centered cubic (fcc) structure and peaks characteristics of TiO2 (anatase phase) with a tetragonal structure. The TEM images showed that the Pd and TiO2 nanoparticles were well distributed in the carbon support showing some clustered regions with nanoparticle sizes between 7 and 8 nm. Cyclic voltammograms showed an increase in current density values after the glycerol adsorption process. Experiments in alkaline direct glycerol fuel cells at 60 °C showed a higher power density for Pd-TiO2/C (70∶30) in comparison to the commercial Pd/C electrocatalyst indicating that the use of the TiO2 co-catalyst with Pd nanoparticles had a beneficial behavior. This effect can be attributed to the electronic effect or to the bifunctional mechanism. Molecules with high-value added glyceraldehyde, hydroxypyruvate and formate were identified as electrochemical reaction products of glycerol on all prepared electrocatalysts. -
Figure 6 Polarization (A-(I)) curves and power density (A-(II)) in a 5 cm2 alkaline direct glycerol fuel cell (ADGFC) at 60 °C, using Pd/C, TiO2/C and Pd-TiO2/C electrocatalysts with different atomic proportions fed with 2.0 mol/L glycerol in a 2.0 mol/L KOH solution and oxygen flux was set to 150 mL min at 85 °C
Table 1 Nominal atomic ratios and atomic ratios obtained by EDX of the Pd-TiO2/C (50∶50, 70∶30 and 90∶10) electrocatalysts synthesized by the sodium borohydride reduction method
Electrocatalyst Nominal atomic ratios (%)
(Pd:TiO2)Atomic ratios EDX (%)
(Pd:TiO2)Pd-TiO2/C 50:50 45:55 Pd-TiO2/C 70:30 68:33 Pd-TiO2/C 90:10 89:11 Table 2 Molecules formation in the partial electro-oxidation reaction of glycerol at different potentials using combined Pd/C and TiO2/C electrocatalysts
Pd TiO2 50% 70% 90% Formate 0.0→0.69 (0.59↑) 0.21 → 0.51 0.34 → 0.74 (0.52↓) 0.0 to 0.70 Hydroxypyruvate 0.0→0.69 (0.59↑) 0.21 → 0.51 0.34 → 0.74
(0.34↓)(0.52↓) 0.0 to 0.70 Glycerate 0.0→0.69 (0.59↑ and 0.69↑) 0.21 → 0.51 0.34 → 0.74
(0.34↓ and 0.44↓)0.0 → 0.62
(0.52↓)0.0 to 0.70 Carbonate 0.0→0.69 (0.59↑ and 0.69↑) 0.21 → 0.51 0.34 → 0.74 (0.34↓ and 0.44↓) 0.0 → 0.62 (0.52↓) 0.0 to 0.70 Carboxylate 0.0→0.69 (0.59↑ and 0.69↑) N.O. 0.54 → 0.74 (0.74↑) (0.62↑) N.O. Symbol used: → : increase to; ↓: less intense; ↑: more intense; N.O.: not observed -
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