Biodegradation and proton exchange using natural rubber in microbial fuel cells

Microbial fuel cells (MFCs) generate electricity from waste but to date the technology's development and scale-up has been held-up by the need to incorporate expensive materials. A costly but vital component is the ion exchange membrane (IEM) which conducts protons between the anode and cathode electrodes. The current study compares natural rubber as an alternative material to two commercially available IEMs. Initially, the material proved impermeable to protons, but gradually a working voltage was generated that improved with time. After 6 months, MFCs with natural rubber membrane outperformed those with anion exchange membrane (AEM) but cation exchange membrane (CEM) produced 109 % higher power and 16 % higher current. After 11 months, polarisation experiments showed a decline in performance for both commercially available membranes while natural rubber continued to improve and generated 12 % higher power and 54 % higher current than CEM MFC. Scanning electron microscope images revealed distinct structural changes and the formation of micropores in natural latex samples that had been employed as IEM for 9 months. It is proposed that the channels and micropores formed as a result of biodegradation were providing pathways for proton transfer, reflected by the steady increase in power generation over time. These improvements may also be aided by the establishment of biofilms that, in contrast, caused declining performance in the CEM. The research demonstrates for the first time that the biodegradation of a ubiquitous waste material operating as IEM can benefit MFC performance while also improving the reactor's lifetime compared to commercially available membranes.