Solar-assisted microbial fuel cells for bioelectricity and chemical fuel generation

Microbial fuel cell (MFC) is an electrochemical device that uses electrogenic bacteria as biocatalysts to decompose organic matter while simultaneously generating bioelectricity. Besides electricity, the bio-electrons generated in the microbial electrogenesis process at the anode can also be used to produce chemical fuels, such as hydrogen gas. However, microbial electrohydrogenesis process does not occur spontaneously due to the thermodynamic barrier for the conversion from protons to hydrogen gas, and therefore an electrical bias has to be supplied to supplement the energy required for the proton reduction. The requirement of external bias adds to the complexity and cost for hydrogen production, making microbial electrohydrogenesis less attractive as a cost-effective energy solution. Alternatively, the energy required to overcome the barrier can be provided by a renewable energy source such as solar light, which is a promising approach that could fundamentally address this issue. Recently, a number of solar-assisted microbial fuel cells have been demonstrated by coupling the conventional MFC with photosynthetic bacteria, semiconductor photoelectrodes, solar cell or photoelectrochemical cell. In these devices, solar energy was utilized to facilitate bioelectricity or hydrogen generation. The demonstration of these new solar-assisted MFC devices opens up new opportunities in the recovery of chemical energy in wastewater for chemical fuel production. This article highlights the recent accomplishments in the solar-assisted MFC technology and discusses the current challenges and future opportunities in the field.