Graphene for energy use is emerging as an exciting topic of research, with breakthrough discoveries hitting the headlines every week.
Supercapacitors, the new paradigm for portable energy, are expected to replace traditional batteries in personal devices such as cellphones, laptop computers, tablets, and even electric vehicles. Supercapacitors can recharge and discharge in just seconds, but can hold enough energy to power a handheld device for several weeks. With supercapacitors, even electric cars could be charged at “electric stations” within a few minutes, with enough “gas” to drive around the whole day. Graphene supercapacitors have existed in research labs for only two years, but the progress has been tremendous.
The recently developed process to make graphene supercapacitors, which is economical and industrially scalable, starts from the widely available graphene oxide. Although the aforementioned development is awesome, a most recent one is a serious competitor in the world of graphene supercapacitors. The recent work radically departs from all known supercapacitors, by using technology’s favorite material – silicon – as the active energy-storing material.
Instead of storing energy in chemical reactions the way batteries do, “supercaps” store electricity by assembling ions on the surface of a porous material. The problem with the concept of using silicon as the porous material for supercaps is that silicon tends to react with chemicals which form the electrolyte, a chief component of any modern energy-storing device.
The novel device, developed at Vanderbilt University, takes care of the silicon reactivity problem by coating the silicon with a layer of graphene. The graphene layer, only several nanometers thin, passivates the porous silicon surface, preventing any reaction with the electrolyte. The graphene smoothly follows the structure of the pores in silicon. The silicon-graphene composite acts as the electrode of the supercap, resulting in large improvements in energy density compared to bare silicon. Taking into account the ubiquity of silicon, this new approach provides an exciting platform for grid-scale as well as integrated (portable) energy storage.