Edge‐Selectively Sulfurized Graphene Nanoplatelets as Efficient Metal‐Free Electrocatalysts for Oxygen Reduction Reaction: The Electron Spin Effect

Abstract

To replace precious platinum (Pt)-based electrocatalysts for cathodic oxygen reduction reaction (ORR), edge-selectively sulfurized graphene nanoplatelets (SGnP) are synthesized as efficient metal-free electrocatalysts simply by ball-milling pristine graphite in the presence of sulfur (S8 ). The resultant SGnPs exhibit remarkable electrocatalytic activity toward ORR with better tolerance to methanol crossover/CO poisoning effects and longer-term stability than those of pristine graphite and commercial Pt/C electrocatalysts. Edge-Selectively Sulfurized Graphene Nanoplatelets as Efficient Metal-Free Electrocatalysts for Oxygen Reduction Reaction: The Electron Spin Effect.

Carbon-Based Metal-Free Electrocatalysis for Energy Conversion, Energy Storage, and Environmental Protection

“…Similarly, the high electronegativity of F atoms can induce adjacent C polarization to create active sites. In addition, S (χ = 2.58), possessing similar electronegativity to C and expected to have low effects on charge distribution and thus low ORR activity, [89] actually facilitates high ORR performance because the spin density in S-doped carbon is slightly higher than that in pure carbon. Instead of the substitution of sp 2 carbon atoms, S in carbon lattices is often in the form of a thiophene-like structure because of its larger atomic radius relative to C. Covalently bonded S, especially sulfur oxide, at zigzag or armchair edges of carbon planes can also create polarized zones that serve as active sites for ORR.…”

“…Instead of the substitution of sp 2 carbon atoms, S in carbon lattices is often in the form of a thiophene-like structure because of its larger atomic radius relative to C. Covalently bonded S, especially sulfur oxide, at zigzag or armchair edges of carbon planes can also create polarized zones that serve as active sites for ORR. In general, a large number of chemical species in the form of either substitution or attachment to sp 2 carbon can induce asymmetric spin density and/or atom charge density to promote ORR electrocatalysis [89].…”

Fe@N‐Graphene Nanoplatelet‐Embedded Carbon Nanofibers as Efficient Electrocatalysts for Oxygen Reduction Reaction

“…The pristine graphite (5.0 g, Alfa Aesar, natural graphite, 100 mesh (<150 μm), 99.9995% metals basis, Lot#14735) was placed into a stainless steel ball‐mill capsule (500 mL) containing stainless steel balls (500.0 g, diameter 5 mm). The capsule was sealed and charged with N 2 (8 bar of cylinder pressure) after five charging–discharging cycles and then fixed in the planetary ball‐mill machine and agitated at 500 rpm for 48 h. The final product was freeze‐dried at −120 °C under a reduced pressure (0.05 mmHg) for 48 h The source of iron (Fe) is the stainless steel balls and ball‐mill capsules 12. PAN (Molecular weight = 150–000, Aldrich Chemical Co.) and N,N ‐dimethylformamide (DMF, Alfa Aesar Co.) were used as a carbon source in the CNFs and a solvent, respectively.…”

“…Although Pt and its alloys are considered the most effective electrocatalysts, having high intrinsic catalytic activity toward ORR,6, 7, 8, 9 they suffer from drawbacks of high cost and poor long‐term stability, which hinder the commercial expansion of Pt‐loaded batteries. In this regard, precious metal‐free catalysts such as carbon materials,10, 11, 12, 13 transition metal oxides,14, 15, 16, 17 and perovskite oxides18, 19 have been investigated as alternatives for the air electrode of metal‐air batteries.…”

“…Ozkan and co‐workers13 attributed the high electrochemical performance of heteroatom‐doped carbon to the improved interaction between carbon and heteroatoms, resulting in an enhanced electron‐donor property of the carbon. Baek and co‐workers fabricated heteroatom‐doped graphene nanoplatelets (GnPs) and reported superior electrochemical activity in an alkaline solution 12. Several research groups have also reported that additional additives such as Fe and Co enhanced the ORR activity in a heteroatom‐doped carbon catalyst 13, 23.…”