Abstract

A composite aerogel with superhydrophobic external surface has been synthesized from reduced graphene oxide and polytetrafluoroethylene taken in a weight ratio of 1 : 1. The porous structure of the aerogel has been studied by the standard contact porosimetry method (SCPM). The porosimetric curves measured with respect to octane and water intersect in the region of small pores, thereby leading to the fact that the specific surface area of the aerogel in water is much larger than that in octane, although octane is known to wet any material almost ideally. This phenomenon, which is referred to as “superhydrophilicity,” is explained by the fact that, in the region of mesopores, a sample swells in water due to the hydration of surface –CO and –COH groups, which have been identified with the help of IR and Raman spectroscopies. Thus, the outside surface of the aerogel granules is superhydrophobic, while their interior is superhydrophilic in the region of small pores. As follows from the SCPM data, the total porosity and specific surface area of the aerogel are substantially larger than those of Vulcan XC-72 carbon black, which is a standard carrier for Pt catalysts used in fuel cells based on proton-exchange membranes. Oxygen electroreduction at the aerogel, containing Pt deposited in an amount of 28 µg/cm², has been studied by the method of rotating disk electrode (RDE) in an aqueous 0.5 M H₂SO₄ solution, and the results obtained have been compared with the data on standard commercial Pt (20%)/Vulcan XC-72 catalyst. It has been shown that the limiting diffusion RDE currents for Pt supported on the hydrophobic–hydrophilic aerogel are markedly higher than those for the standard catalyst because of the easier access of oxygen to the reaction zone as compared with hydrophilic Vulcan XC-72 carbon black carrier.

中文翻译：

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具有超亲水和超疏水特性的石墨烯基气凝胶及其在分子氧电还原中的应用

摘要

由还原氧化石墨烯和聚四氟乙烯以 1:1 的重量比合成具有超疏水外表面的复合气凝胶。通过标准接触孔隙率法 (SCPM) 研究了气凝胶的多孔结构。相对于辛烷和水测量的孔隙率曲线在小孔区域相交，从而导致水中气凝胶的比表面积远大于辛烷中的比表面积，尽管已知辛烷几乎可以润湿任何材料理想情况下。这种被称为“超亲水性”的现象的解释是，在中孔区域，由于表面 -CO 和 -COH 基团的水合作用，样品在水中溶胀，这已在帮助下鉴定IR 和拉曼光谱。因此，气凝胶颗粒的外表面是超疏水的，而它们的内部在小孔区域是超亲水的。从 SCPM 数据可以看出，气凝胶的总孔隙率和比表面积明显大于 Vu​​lcan XC-72 炭黑，Vulcan XC-72 炭黑是基于质子交换膜的燃料电池中使用的 Pt 催化剂的标准载体。气凝胶上的氧电还原，含有 28 µg/cm2 沉积量的 Pt²，已经通过在0.5 MH ₂ SO ₄水溶液中旋转圆盘电极（RDE）的方法研究，并且获得的结果已经与标准商业Pt（20%）/Vulcan XC-72催化剂的数据进行比较。研究表明，与亲水性 Vulcan XC-72 炭黑载体相比，疏水-亲水气凝胶上负载的 Pt 的极限扩散 RDE 电流明显高于标准催化剂，因为氧气更容易进入反应区.