Heteroatoms co-Doping (N, F) to the Porous Carbon Derived from Spent Coffee Grounds as an Effective Catalyst for Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cells

Abstract

Toward development of alternative metal-free oxygen reduction reaction catalyst, engineering heteroatoms and tuning defects, pore geometry in porous carbon is explored in this study. Simultaneous co-doping of nitrogen and fluorine heteroatoms to porous carbon matrix derived from spent coffee grounds is synthesized and studied for their structural and electrochemical properties. Microscopic analysis of N-F co-doped coffee carbon (N-F/CC) undergoes morphological evolution in its textural properties includes geometrical surface area, pore structure and defects associated with them, features responsible for creating active sites toward ORR activity. N-F/CC catalyst exhibits excellent ORR catalytic activity, methanol and carbon monoxide tolerance in both acidic and alkaline media which makes it highly potential as metal-free oxygen reduction reaction catalyst for polymer electrolyte fuel cell. The developed catalyst is subjected to 10,000 repeated potential cycles in both media and is stable with no degradation in ORR activity. XPS analysis of N-F/CC catalyst revealed the presence of N in the forms of pyridinic-N, pyrrolic-N, graphitic-N, active species and F in the forms of C-F ionic and C-F semi-ionic active forms. Co-existence of all these active species induces the maximum C-C bond polarization, charge re-distribution and high spin densities in the carbon matrices and synergistically ORR activity.