Effect of axial ligand on the performance of hemin based catalysts and their use for fuel cells.

• A new cascade type CNT/PEI/IPA-Hemin/GOx catalyst is introduced. • Onset potential for HRR is positively shifted due to adoption of axial ligands. • Axial ligand forms the coordination bonds with Fe core ions within hemin. • MPD of membraneless EBC using a new cathodic catalyst is 66.0 μWcm⁻². • CNT/PEI/IPA-Hemin/GOx plays its role well as cathodic catalyst. A new cascade type cathodic catalyst containing hemin and glucose oxidase (GOx) is suggested for enhancing the performances of enzymatic biofuel cells (EBCs). In the cathodic catalyst, the upper GOx layer generates hydrogen peroxide (H 2 O 2) by glucose oxidation reaction (GOR), and then actual cathodic current is determined by H 2 O 2 reduction reaction (HRR) catalyzed by hemin, using the pre-produced H 2 O 2. The reaction potential of hemin is positively shifted by the formation of coordinate bond between its core ions and amine groups, meaning that that of HRR deciding reduction onset potential of the catalyst is positively shifted. As materials providing the ligand containing amine groups, polyethyleneimine (PEI) and imidazole propionic acid (IPA) are considered. According to evaluations, the reaction potential for HRR is favorably moved as the amounts of available ligand and coordinate bond increase. When IPA is applied, the reduction onset potential for HRR is shifted from 0.4 to 0.51 V and reduction reaction rate also increases from 55 to 86 μAcm⁻². Based on that, the EBC using catalyst containing IPA shows superior performances, such as maximum power density of 66 μWcm⁻² and open circuit voltage of 0.65 V. [ABSTRACT FROM AUTHOR]