Carbon-nanotube-caged microbial electrodes for bioelectrocatalysis

Fundamental insight into redox enzyme-based bioelectrocatalysis

Redox enzymes can work as efficient electrocatalysts. The coupling of redox enzymatic reactions with electrode reactions is called enzymatic bioelectrocatalysis, which imparts high reaction specificity to electrode reactions with nonspecific characteristics. The key factors required for bioelectrocatalysis are hydride ion/electron transfer characteristics and low specificity for either substrate in redox enzymes. Several theoretical features of steady-state responses are introduced to understand bioelectrocatalysis and to extend the performance of bioelectrocatalytic systems. Applications of the coupling concept to bioelectrochemical devices are also summarized with emphasis on the achievements recorded in the research group of the author.

Shewanella putrefaciens powered microfluidic microbial fuel cell with printed circuit board electrodes and soft-lithographic microchannel

Microfluidic microbial fuel cells (μ-MFCs) have received considerable attention due to their ability to generate green and qualitative self-sustainable energy. Several electrodes and device fabrication methodologies, and various electrochemically active bacteria (EABs), along with their effect on MFC performance with various operating parameters, have been well reported. However, shorter life, lower throughput, and high operating and maintenance overheads are major impediments to their development towards commercialization. In this context, simple and cost-effective bioelectrodes using printed circuit board (PCB) and a polymer based microchannel have been fabricated using modern photolithography and soft-lithography techniques respectively. Furthermore, the etched PCB electrodes were patterned with multi-walled carbon nanotubes (MWCNT). Subsequently, these bioelectrodes were assembled over a Y-shaped microchannel and tested under a co-laminar microfluidic flow environment powered by Shewanella putrefaciens. Various volumetric bacterial experiments and flow rate studies have also been conducted to find the most appropriate optimum bacterial volume and power efficiency. Subsequently, extensive potentiometric electrochemical studies, such as Open Circuit Potential (OCP) and polarization analysis, were accomplished using electrochemical workstation. This well-developed handheld μ-MFCs yields a maximum open circuit potential 395 mV with maximum power density of 239.2 μW/cm² (3.271 mA/cm²) at optimized parameters.