Studies On Cobalt Doped Indole Derivatives Modified Carbon- Supported Catalysts For Oxygen Reduction Reaction

Fuel cells have attracted much attention due to their high efficiency and environmental friendliness. Oxygen reduction reaction (ORR) in cathode is an important factor that hinders the development of fuel cell. The traditional catalyst of ORR is carbon supported platinum (Pt/C). Pt has excellent catalytic activity. However, the scarcity of Pt in nature is a big problem for its commercial applications. So development of non-precious metal catalysts has become one of the most heated researches in fuel cells. This work has studied the use of indole and indole carboxylic acid modified carbon supported non-precious metal composites as the oxygen reduction reaction catalysts. The study discussed the catalytic mechanism in acidic and alkaline medium,and also test their electrochemical properties and validated their stability in fuel cells.Cobalt coordination compounds with indole and indole carboxylic acid were synthesized using the hydrothermal method. The catalytic cluster formation process during pyrolysis was first investigated through the in-situ transmission electron microscope (TEM) and high resolution TEM observations. Using Fourier infrared spectrum (FT IR), X-ray powder diffraction (XRD), nuclear magnetic resonance spectroscopy (NMR), inductively coupled plasma emission spectrum (ICP) analysis method to analyze material characterization. The catalysts electrochemical properties were tested by cyclic voltammetry (CV) and rotating disk method (RDE), and the key factor that influences the catalytic activity in different medium was also disscussed.Studies had shown that both indole modified carbon supported cobalt catalyst (Co-indole/ BP) and indole carboxylic acid (indole-3-carboxylic acid:ICA, indole-3-acetic acid:IAA, indolyl-3-propionic acid:IPA,3-Indolybutyric acid:IBA) modified carbon supported cobalt catalyst, had good ORR catalytic activity. The Co-IAA/BP exhibited higher oxygen reduction reaction (ORR) current in alkaline electrolyte and more positive ORR potential in acidic electrolyte than the carbon supported Co-indole/BP. Co3O4 crystals were created on the carbon support after pyrolysis of the Co-indole/BP and Co-IAA/BP at 900℃ under Argon atmosphere. The pyrolyzed Co-indole/BP and Co-IAA/BP presented higher ORR current and potential in both acidic and alkaline electrolytes than their origins. Moreover, the ORR on-set potential, kinetic current and electron transfer number of the pyrolyzed Co-IAA/BP were higher than the values of the pyrolyzed Co-indole/BP.Co-IAA/BP and pyrolyzed Co-indole/BP and Co-IAA/BP catalyst in acidic medium had good ORR catalytic activity, because Oxygen in the Co-IAA and Co3O4 draws protons to enhance the ORR occurring in the acidic electrolyte. The formation of the catalytic site composed of electrophilic center coupled with nucleophilic center is the key to develop the ORR catalyst with high electrocatalytic activity in the acidic electrolyte.Based on the study above, a series of fuel cell test had been performed using the synthesized composites as cathode materials. And the results revealed that, pyrolyzed Co-IAA/BP showed worse ORR performance than 10% Pt/C in direct methanol fuel cell (DMFC), But it has better performance compared to 10% Pt/C catalyst in direct sodium borohydride fuel cell(DBFC). Means that the catalyst used for direct sodium borohydride fuel cell can be a replace of 10% Pt/C. The cathode life test showed that the pyrolyzed Co-indole/BP and Co-IAA/BP has good stability.