Iakunkov Artem, Skrypnychuk Vasyl, Nordenström Andreas, Shilayeva Elizaveta A, Korobov Mikhail, Prodana Mariana, Enachescu Marius, Larsson Sylvia H, V Talyzin Alexandr
Department of Physics, Umeå University, Umeå, SE-901 87, Sweden.
Phys Chem Chem Phys. 2019 Aug 15;21(32):17901-17912. doi: 10.1039/c9cp03327k.
Activated reduced graphene oxide (a-rGO) is a material with a rigid 3D porous structure and high specific surface area (SSA). Using variation of activation parameters and post-synthesis mechanical treatment we prepared two sets of materials with a broad range of BET (N2) SSA ∼1000-3000 m2 g-1, and significant differences in pore size distribution and oxygen content. The performance of activated graphene as an electrode in a supercapacitor with KOH electrolyte was correlated with the structural parameters of the materials and water sorption properties. a-rGO is a hydrophobic material as evidenced by the negligibly small BET (H2O) SSA determined using analysis of water vapor sorption isotherms. However, the total pore volume determined using water vapor sorption and sorption of liquid water is almost the same as the one found by analysis of nitrogen sorption isotherms. Ball milling is found to provide an improved bulk density of activated graphene and collapse of all pores except the smallest ones (<2 nm). A decrease in the activation temperature from 850 °C to 550 °C is found to result in materials with a narrow micropore size distribution and increased oxygen content. Elimination of mesopores using ball milling or a lower activation temperature provided materials with better specific capacitance despite a significant decrease (by ∼30%) of the BET (N2) SSA. The best gravimetric and volumetric capacitances in KOH electrolyte were achieved not for samples with the highest value of the BET (N2) SSA but for materials with 80-90% of the total pore volume in micropores and an increased BET (H2O) SSA. Comparing the performance of electrodes prepared using rGO and a-rGO shows that a more hydrophilic surface is favorable for charge storage in supercapacitors with KOH electrolyte.
活化还原氧化石墨烯（a-rGO）是一种具有刚性三维多孔结构和高比表面积（SSA）的材料。通过改变活化参数和合成后机械处理，我们制备了两组材料，其BET（N₂）SSA范围广泛，约为1000 - 3000 m² g⁻¹，且孔径分布和氧含量存在显著差异。活化石墨烯作为超级电容器中使用KOH电解质的电极时，其性能与材料的结构参数和水吸附性能相关。a-rGO是一种疏水材料，通过对水蒸气吸附等温线的分析测定，其BET（H₂O）SSA可忽略不计。然而，通过水蒸气吸附和液态水吸附测定的总孔体积与通过氮吸附等温线分析得到的总孔体积几乎相同。发现球磨可提高活化石墨烯的堆积密度，并使除最小孔（<2 nm）外的所有孔坍塌。发现将活化温度从850℃降至550℃会导致材料具有窄的微孔尺寸分布和增加的氧含量。尽管BET（N₂）SSA显著降低（约30%），但使用球磨或较低活化温度消除中孔后得到的材料具有更好的比电容。在KOH电解质中，最佳的重量和体积电容并非由BET（N₂）SSA最高的样品实现，而是由微孔中总孔体积占80 - 90%且BET（H₂O）SSA增加的材料实现。比较使用rGO和a-rGO制备的电极性能表明，在使用KOH电解质的超级电容器中，更亲水的表面有利于电荷存储。
