O₂ Reduction on Graphite and Nitrogen-Doped Graphite:  Experiment and Theory

Abstract

An experimental and theoretical study of electroreduction of oxygen to hydrogen peroxide is presented. The experimental measurements of nitrided Ketjenblack indicated an onset potential for reduction of approximately 0.5 V (SHE) compared to the onset potential of 0.2 V observed for untreated carbon. Quantum calculations on cluster models of nitrided and un-nitrided graphite sheets show that carbon radical sites formed adjacent to substitutional N in graphite are active for O 2 electroreduction to H 2 O 2 via and adsorbed OOH intermediate. The weak catalytic effect of untreated carbon is attributed to weaker bonding of OOH to the H atom-terminated graphite edges. Substitutional N atoms that are far from graphite sheet edges will be active, and those that are close to the edges will be less active. Interference from electrochemical reduction of H atoms on the reactive sites is considered, and it is shown that in the potential range of H 2 O 2 formation the reactive sites are not blocked by adsorbed H atoms.

Hierarchically porous carbons with optimized nitrogen doping as highly active electrocatalysts for oxygen reduction

“…It is normally believed that pyridinic N doped at the edge of the graphitic layers is effective for ORR as such N-doping can reduce the energy barrier for oxygen adsorption on adjacent carbon atoms, and accelerate the rate-limiting firstelectron transfer during the ORR 20 . Quantum theory calculation and previous experimental results also suggested that doping of quaternary N into graphene planes could induce a non-uniform electron distribution and short C-N bonds, comparable to O-O bonds, which would facilitate O 2 adsorption and subsequent disassociation/weakening of O ¼ O bonds 19,21 .…”

“…This can be explained by the reactions between NH 3 and oxygen functionalities located on the carbon surface, possibly resulting in new nitrogen-containing active sites 12,29 . Surprisingly, the final nitrogen content of meso/micro-PoPD (3.15 at%) obtained with NH 3 activation was significantly lower than that of meso-PoPD (9.5 at%), although NH 3 was generally recognized as a nitrogen precursor for preparing N-doped carbon catalysts [10][11][12]18,19 . We reason that, besides the surface reaction with oxygen species, NH 3 molecules can also react with the carbon matrix under high temperature, preferably with disordered carbon phases [30][31][32] .…”

“…Nitrogen-doped nanostructured carbon materials represent important candidates as metal-free electrocatalysts for ORR because of their unique electronic properties and structural features [18][19][20] . In spite of some significant achievements attained by the careful selection of suitable precursors and the optimization of nanostructuring process 18,[21][22][23][24][25][26][27][28] , the ORR performance of the reported metal-free catalysts is still inferior to the state-of-the-art Pt/C catalyst in terms of half-wave potential and does not yet warrant implementation in real energy conversion/storage devices.…”

Design of Iron(II) Phthalocyanine‐Derived Oxygen Reduction Electrocatalysts for High‐Power‐Density Microbial Fuel Cells

“…The performance is effected dramatically by the MFC design,1 operating temperature,74 altitude above sea level, electrolyte utilized (different solution conductivity),43 bacteria utilized (e.g., single or mixed culture),1 organic compounds utilized (e.g., lactate, acetate, fumarate, etc. ),3, 75 organics concentration,74 and the presence or absence of membranes 66. Several other studies demonstrated the utilization of Fe‐based catalysts with excellent performances and superiority over platinum‐based cathodes22, 23 or AC‐based cathodes 43…”

“…Nitrogen has been identified to have a positive effect on the ORR owing to its ability to improve the electronic properties 64, 65, 66. However, excess nitrogen concentrations may be harmful to the overall performance, as it decreases the conductivity of the material.…”