Combined Effect of Porosity and Surface Chemistry on the Electrochemical Reduction of Oxygen on Cellular Vitreous Carbon Foam Catalyst
Combined Effect of Porosity and Surface Chemistry on the Electrochemical Reduction of Oxygen on Cellular Vitreous Carbon Foam Catalyst
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DOI：
10.1021/acscatal.7b01977
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发表时间：
2017-11-01
期刊：
影响因子：
12.9
通讯作者：
Bandosz, Teresa J.
中科院分区：
文献类型：
--
作者：
Encalada, Jimmy;Savaram, Keerthi;Bandosz, Teresa J.
提出了一种新的O-2还原机理，该机理遵循的原理不同于一般公认的描述杂原子掺杂碳上ORR还原的原理。它是基于氧在狭窄的疏水孔中强烈吸附的能力。在这方面，合成了多孔玻璃状碳泡沫-氧化石墨烯复合材料。这些材料掺杂有硫和氮和/或在950摄氏度下进行热处理，以改变其表面化学性质。所得样品呈现大孔/微孔性质，并作为ORR催化剂进行测试。为了了解还原过程，从纹理和化学角度对其表面进行了广泛的表征。所施加的处理显著改变了小微孔的体积和表面亲水性/极性特征。结果表明，最佳样品的电子转移数在3.87 ~ 3.96之间，起始电位达到0.879 V。值得注意的是，表现最好的样品具有最高体积的小于0.7nm的孔，而没有杂原子掺杂。疏水性和由这些孔提供的将氧气拉入内部的强吸附力是所观察到的优异性能的可能原因。这些孔的体积的减少导致催化性能的降低。当表面用杂原子改性时，由于诱导的亲水性，性能进一步恶化。
A new mechanism of O-2 reduction, which follows principles different from those generally accepted for describing ORR reduction on heteroatom-doped carbons, is suggested. It is based on the ability of oxygen to strongly adsorb in narrow hydrophobic pores. In this respect, a cellular vitreous carbon foam-graphene oxide composite was synthesized. The materials were doped with sulfur and nitrogen and/or heat-treated at 950 degrees C in order to modify their surface chemistry. The resultant samples presented a macro-/microporous nature and were tested as ORR catalysts. To understand the reduction process, their surfaces were extensively characterized from texture and chemistry points of view. The treatment applied markedly changed the volumes of small micropores and the surface hydrophilicity/polarity character. The results showed that the electron transfer number was between 3.87 and 3.96 and the onset potential reached 0.879 V for the best-performing sample. It is noteworthy that the best-performing sample has the highest volume of pores smaller than 0.7 nm while there was no heteroatom doping. The hydrophobicity and the strong adsorption forces provided by these pores to pull oxygen inside are the possible reasons for the observed excellent performance. A decrease in the volume of these pores resulted in a decrease in the catalytic performance. When the surface was modified with heteroatoms, the performances worsened further because of the induced hydrophilicity.