Highly dispersed CoPx nanoparticles supported on carbon cloth for the enhanced catalytic performance of methanol electro-oxidation
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摘要: 直接甲醇燃料电池(DMFC)是一种有潜力的商用燃料电池技术,目前贵金属阳极材料昂贵的价格阻碍其发展。开发分散均匀粒径分布窄的金属磷化物催化剂仍然是一个挑战。本研究通过原子层沉积法(ALD)在碳布上沉积CoOx,然后经过磷化处理获得CoPx。通过改变ALD臭氧脉冲(ALD-O3)的循环数,调控CoOx(ALD-CoOx)在碳布上的成核生长方式,获得粒径小、分布均匀的CoPx纳米粒子。经过优化后的CoPx纳米催化剂(CoPx/40-CC)在碱性溶液中对甲醇电催化氧化反应表现出优异的活性(153 mA/cm2),高于浸渍法制备的催化剂(Imp-CoPx/CC),尽管CoPx/40-CC的CoPx负载量低于Imp-CoPx/CC。结果表明,甲醇电催化氧化过程中的电子转移和传质动力学得到了提高,这得益于CoPx较小的粒径和均匀的分布。Abstract: Direct methanol fuel cell (DMFC) is a potential commercial fuel cell technology that is presently hindered by the expensive noble metal materials of the anode. Developing a method to obtain a uniformly dispersed metal phosphide catalyst with narrow size distribution is still a challenge. In this work, cobalt oxide was deposited on carbon cloth (CC) through atomic layer deposition (ALD), then cobalt phosphide was obtained after the phosphorization process. By changing the number of ALD-based ozone pulses (ALD-O3) for CC, the nucleation and growth modes of cobalt oxide (ALD-CoOx) on the CC were regulated, and CoPx nanoparticles with small particle size and uniform distribution were obtained. The optimized CoPx-based catalyst with 40 cycles of ALD-O3 treatment (CoPx/40-CC) exhibits excellent activity (153 mA/cm2) toward methanol electrocatalytic oxidation reaction in the alkaline solution, which is higher than the catalyst prepared by impregnation (Imp-CoPx/CC), although the CoPx loading of CoPx/40-CC is lower than that of Imp-CoPx/CC. The results indicate that the enhanced activity benefits from the small particle size and the uniform CoPx distribution, which promote the electron-transfer and mass transport kinetics of the methanol electro-oxidation process.
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Figure 6 (a) CVs, (b) bar graph(@1.7 V vs RHE), and (c) EIS curves of CoPx/n-CC and Imp-CoPx/CC for MOR in 1 mol/L KOH + 1 mol/L methanol, (d) Tafel curves and (g) chronoamperometric (CA) results of CoPx/10-CC, CoPx/40-CC, CoPx/75-CC, and Imp-CoPx/CC, (e) LSV of CoPx/40-CC in 1 mol/L KOH, with and without 1 mol/L methanol, (f) CV curves of CoPx/40-CC in 1 mol/L KOH +1 mol/L CH3OH solution at different scanning rates (10–200 mV/s), where the inset shows the proportionality of current density (@1.7 V vs RHE) vs the square root of the scan rate, (h) CVs and (i) bar graph (@1.7 V vs RHE) of nCoPx/40-CC and Imp-CoPx/CC for MOR in 1 mol/L KOH + 1 mol/L methanol
Table 1 Comparison of the MOR performance of CoPx/40-CC with those of other catalysts reported in the literatures.
Electrocatalyst Electrolyte solution Current density at 1.7 V
vs RHE/(mA·cm−2)Potential at 10 mA/cm2 /V Reference CoPx/40-CC 1 mol/L KOH +
1 mol/L methanol153 1.39 this work CoPx hollow spheres 1 mol/L KOH +
1 mol/L methanol31 1.62 [19] CoP nanoflowers 1 mol/L KOH +
1 mol/L methanol1.59 [34] Hollow CoP OCHs 1 mol/L KOH +
1 mol/L methanol1.37 [35] Porous CoP NSs 1 mol/L KOH +
1 mol/L methanol1.42 [35] Co3(PO4)2 nanosphere 1 mol/L KOH +
1 mol/L methanol146 [36] -
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