Indole‐based novel organic anode catalyst for glucose electrooxidation

Abstract

The development of organic-based metal-free catalysts is vital for the commercialization of fuel cells. At present, novel indole derivatives (2-((5-(5-[1-Methyl-2-phenyl-1H-indol-3-yl] thiophen-2-yl)furan-2-yl) methylene) malononitrile ITFM and 2-((5′-(1-Methyl-2-phenyl-1H-indol-3-yl)-(2,2′-bithiophen)-5-yl)methylene) malononitrile ITTM were designed, synthesized, and their electrochemical properties were investigated. First, one-pot two-step cyclization reactions were applied for the synthesis of intermediate 1-methyl-2-phenyl-3-(thiophen-2-yl)-1H-indole (5). Then, halogenation reaction and Suzuki-Miyaura coupling reactions were used for the formation of intermediate 5-(5-[1-methyl-2-phenyl-1H-indol-3-yl] thiophen-2-yl) furan-2-carbaldehyde (8) and 5′-(1-methyl-2-phenyl-1H-indol-3-yl)-[2,2′-bithiophene]-5-carbaldehyde (12). Finally, ITFM and ITTM were isolated in 76% and 60% yields via condensation reactions. Then, glucose electrooxidation performance of these indole derivatives were examined by using Cyclic Voltammetry (CV), Chronoamperometry (CA), and Electrochemical Impedance Spectroscopy (EIS) in 0.5 M glucose alkaline solution. ITTM exhibited the best glucose electrooxidation activity because the specific activity of ITFM was found as 0.46 mA/cm2, and ITTM gave the 0.52 mA/cm2. CA results revealed that the specific activity and stability of ITTM were greater than ITFM catalysts. EIS results were also in agreement with CV and CA results that the charge transfer resistance (Rct) of ITFM was greater than ITTM displaying that ITTM improved charge-transfer kinetics. As a result, an indole derivative-based catalyst is a new generation of environmentally friendly and alternative catalyst for direct glucose fuel cells.