Heteroatom Engineering and Co-Doping of N and P to Porous Carbon Derived from Spent Coffee Grounds as an Efficient Electrocatalyst for Oxygen Reduction Reactions in Alkaline Medium

摘要

This paper describes the synthesis of low cost electrocatalyst for oxygen reduction reaction (ORR) from spent coffee grounds (SCGs) through heteroatom engineering and simultaneous codoping of N and P. The co-doping of N and P to coffee carbon (N-P/CC) brings maximum defect sites in the catalyst which are favourable for ORR in relation to the individual heteroatom doped catalyst. Microscopic analysis confirms that N-P codoped coffee carbon (N-P/CC) undergoes slight structural changes by altering its porosity as well as surface area. Electrochemical studies confirm that, N-P/CC has superior catalytic activity with no effect to CO which makes it highly desirable as a metal-free electrocatalyst for ORR. The developed catalyst is subjected to 10,000 repeated potential cycles in alkaline media and is found only ~30 mV loss in its E1/2 potential, while the drop in E_(1/2) is about ~180 mV from its original value even after 1000 potential cycles for the commercial Pt/C catalyst. XPS analysis for NP/CC shows the presence of active pyridinic-N, graphitic-N species and active P-C and P-O bonds. Co-existence of all these species induces maximum polarization of C-C bonds in the carbon matrix and synergistically enhances the ORR behaviour in alkaline medium