Recent developments of graphene electrodes in bioelectrochemical systems

Sustainable societies require development of cost-effective methods for harnessing energy from wastes and wastewater, and alternatively capturing this energy to make other useful chemicals with simultaneous wastes and wastewater treatment. Recently developed bioelectrochemical systems (BESs) that use microorganisms to catalyze different electrochemical reactions are promising for capturing the energy in wastes and wastewater for diverse purposes. A BES is called a microbial fuel cell (MFC) if electricity is generated and the Gibbs free energy change of the corresponding reaction is negative. Conversely, when the Gibbs free energy change of the overall reaction is positive, power needs to be supplied to drive this non-spontaneous reaction, and this BES is regarded as a microbial electrolysis cell (MEC). The electrode character is considered to be a key factor for triggering the applicable BESs. Graphene has been recently used as the electrode and investigated in BESs because of its unique structure and excellent properties. Here, an up-to-date review is provided on the recent research and development in BES-based graphene, particularly in MFC-based graphene. The recent pristine graphene, doped graphene, and supported graphene research in MFCs is described in detail. The potential applications of graphene in MECs and the scientific and technical challenges are also discussed.