A new biocatalyst employing pyrenecarboxaldehyde as an anodic catalyst for enhancing the performance and stability of an enzymatic biofuel cell

A new enzyme catalyst consisting of pyrenecarboxaldehyde (PCA) and glucose oxidase (GOx) immobilized on polyethyleneimine (PEI) and a carbon nanotube supporter (CNT/PEI/[PCA/GOx]) is suggested, and the performance and stability of an enzymatic biofuel cell (EBC) using the new catalyst are evaluated. Using PCA, the amount of immobilized GOx increases (3.3 U mg−1) and the electron transfer rate constant of the CNT/PEI/[PCA/GOx] is promoted (11.51 s−1). Also, the catalyst induces excellent EBC performance (maximum power density (MPD) of 2.1 mW cm−2), long-lasting stability (maintenance of 93% of the initial MPD after 4 weeks) and superior catalytic activity (flavin adenine dinucleotide redox reaction rate of 0.62 mA cm−2 and Michaelis–Menten constant of 0.99 mM). These characteristics are ascribed to effects of (i) electron collection due to hydrophobic interactions, (ii) electron transfer pathways due to π-conjugated bonds and (iii) enzyme stabilization due to π-hydrogen bonds that are newly induced by the PCA/GOx composite. The existence of such positive interactions is properly verified using X-ray photoelectron spectroscopy and enzyme activity measurements. Fuel cells that power medical implants using body-friendly materials stand to benefit from a new catalyst with extra-tight enzyme grip. Glucose oxidase is protein complex that catalytically oxidizes various substrates, including glucose, glycerol and water, and neutral pH. Prof. Yongchai Kwon from Seoul National University of Science and Technology and co-workers now report that modifying outer perimeter of glucose oxidase with allotropes of carbon with a cylindrical nanostructure improves its use in enzymatic biofuel cells. The additional polycyclic aromatic hydrocarbon consisting of four fused benzene rings, called pyrenecarboxaldehydes, enabled strong immobilization of the protein onto a conductive support containing similarly shaped carbon nanotubes. The team identified three new bonding interactions between the biocatalyst and the support that improved electron flow and boosted enzyme stabilization, factors that enhanced the power output and longevity of prototype biofuel cells. New enzyme catalyst consisting of pyrenecarboxaldehyde (PCA) and glucose oxidase (GOx) immobilized on polyethyleneimine and carbon nanotube (CNT/PEI/[PCA/GOx]) is developed with performance and stability evaluations of enzymatic biofuel cell (EBC) using the new catalyst. By employment of PCA, the amount of immobilized GOx increases and electron transfer of CNT/PEI/[PCA/GOx] is facilitated. With that, superior EBC performance, long-lasting stability and excellent catalytic activities are gained. Such results are attributed to effects of (i) electron collection by hydrophobic interactions, (ii) electron transfer by π-conjugated bonds and (iii) enzyme stabilization by π-hydrogen bonds. Validity of such three positive effects is proved by various measurements.