Graphene enriched with pyrrolic coordination of the doped nitrogen as an efficient metal-free electrocatalyst for oxygen reduction

Abstract

We report an efficient template-free synthetic route for the preparation of mesoporous nitrogen-doped graphene (NGE) containing a high weight percentage of pyrrolic nitrogen, good specific surface area and comparable electrochemical oxygen reduction activity as that of the state-of-the-art 40 wt% Pt/C catalyst. The desired coordination of nitrogen in the carbon framework of graphene has been conceived by a mutually assisted redox reaction between graphene oxide (GO) and pyrrole, followed by thermal treatment at elevated temperatures. NGE exhibits a high surface area of 528 m 2 g À1 and a pore diameter of $3 to 7 nm. The heat treatment temperature plays a pivotal role in establishing the desired pyrrolic coordination of nitrogen in graphene for the electrochemical oxygen reduction reaction. The NGE sample obtained after heat treatment at 1000 C (NGE-1000) has 53% pyrrolic nitrogen content compared to the similar samples prepared by treating at low temperatures. Most importantly, NGE-1000 has displayed a significantly low overpotential for oxygen reduction with the onset potential very closely matching that of the commercial 40 wt% Pt/C. It is noteworthy that the reaction involves the desired 4 electron transfer as observed in the case of the Pt based electrocatalysts, leading to a significantly high kinetic current density of 6 mA cm À2 at À0.2 V. Moreover, the fuel tolerance and durability under the electrochemical environment of the NGE catalyst is found to be superior to the Pt/ C catalyst.

Near-edge x-ray absorption fine structure spectroscopy study of nitrogen incorporation in chemically reduced graphene oxide

“…This is further rationalized when considering literature assignments of pyridinic and pyrrolic nitrogen atoms, which have been observed in the range between $398.2-398.6 eV and 399.5-400.0 eV, respectively, in molecular compounds as well as nitrogen-doped carbons. 23,40,41,46 The RGO samples prepared by hydrazine reduction of GO show strikingly similar features to the standards with two prominent peaks centered at 398.6-399.4 eV and 400.2-400.7 eV. The lack of planarity that can be introduced at graphene edges due to the presence of adjacent functional groups can potentially strain the C-N bonds and alter their electronic coupling with the conjugated p system, slightly altering the XPS chemical shift values.…”

Urea-treated carbon nanofibers as efficient catalytic materials for oxygen reduction reaction

“…Although carbon nanofibers (CNFs) with certain content of nitrogen could be obtained simply by the carbonization of electrospun polyacrylonitrile (PAN) nanofibers, the resulting CNFs show poor catalytic activity toward ORR. In fact, the nitrogen types in the carbons played an important role on the catalytic ability [14]. Qiu et al carbonized the electrospun PAN nanofibers in NH 3 leading to the high content of pyrrolic-N and superior electrocatalytic activity toward ORR [15].…”

Highly efficient cathode catalyst layer based on nitrogen-doped carbon nanotubes for the alkaline direct methanol fuel cell

“…graphene [10,[23][24][25][26][27][28][29][30][31][32][33], carbon nanotubes [11,20,21,[34][35][36][37][38][39][40][41][42][43], carbon nanofibers [12,[44][45][46][47], mesoporous carbon [15,22], graphitic carbon [48,49], carbon spheres [19,[50][51][52][53], carbon nanocages 4 [54], flower-like carbon [55], carbon aerogel [56,57], vesicular carbon [58], nanodiamonds [59]) relatively few have been tested in actual fuel cell conditions [58,[60][61][62]…”