High surface area carbon xerogels – Microwave vs. conventional activation with KOH
Resorcinol-formaldehyde xerogels were chemically activated using potassium hydroxide under different activation conditions of time, temperature and heating mechanism. A study of the activation time showed that carbon xerogels with a well-developed porosity (SBET around 2200 m2 g-1) can be produced in the range of 6-30 minutes. It was found that by means of short exposures to microwaves it is possible to partially preserve the original mesoporosity of the precursor and to achieve a higher volume of narrower micropores. However, under conventional heating the mesoporosity created during the synthesis of the organic precursor was destroyed.
In recent years, carbon gels have attracted a great deal of attention for energy applications due to certain useful features that include: a unique three-dimensional nanonetwork, a tailored pore texture according to the synthesis protocol used, a high electrical conductivity and the possibility of using them without the need for binding substances (1, 2). The main drawback of these kind of carbonaceous materials lies in the synthesis process because, by means of conventional methods, at least 24 hours are required to produce xerogels with a significant textural development (3). This limitation has recently been solved through the use of microwave technology, as evidenced by the work of Calvo et al., and Juárez-Pérez et al. (2, 4). Such works demonstrate that it is possible to prepare xerogels analogous to those that are conventionally synthesized, but with a very considerable saving of time (about 5 hours as opposed to several days in conventional processes).
Once the problem of the large and tedious synthesis methodology has been solved, another factor that needs to be improved is the development of their pore texture. The specifi ...