BCN Graphene as Efficient Metal‐Free Electrocatalyst for the Oxygen Reduction Reaction

Abstract

The cathodic oxygen reduction reaction (ORR) is an important process in fuel cells and metal-air batteries. [1][2][3] Although Pt-based electrocatalysts have been commonly used in commercial fuel cells owing to their relatively low overpotential and high current density, they still suffer from serious intermediate tolerance, anode crossover, sluggish kinetics, and poor stability in an electrochemical environment. This, together with the high cost of Pt and its limited nature reserves, has prompted the extensive search for alternative low-cost and high-performance ORR electrocatalysts. In this context, carbon-based metal-free ORR electrocatalysts have generated a great deal of interest owing to their low-cost, high electrocatalytic activity and selectivity, and excellent durability. [4][5][6][7][8][9] Of particular interest, we have previously prepared vertically aligned nitrogendoped carbon nanotubes (VA-NCNTs) as ORR electrocatalysts, which are free from anode crossover and CO poisoning and show a threefold higher catalytic activity and better durability than the commercial Pt/C catalyst. [4] Quantum mechanics calculations [4] indicate that the enhanced catalytic activity of VA-NCNTs toward ORR can be attributed to the electron-accepting ability of the nitrogen species, which creates net positive charges on the CNT surface to enhance oxygen adsorption and to readily attract electrons from the anode for facilitating the ORR. Uncovering this new ORR mechanism in nitrogen-doped carbon nanotube electrodes is significant as the same principle could be applied to the development of various other metal-free efficient ORR catalysts for fuel-cell applications and even beyond fuel cells. Indeed, recent intensive research efforts in developing metal-free ORR electrocatalysts have led to a large variety of carbon-based metal-free ORR electrocatalysts, including heteroatom (N, B, or P)-doped carbon nanotubes, graphene, and graphite. [4][5][6][7][8][9][10][11][12][13][14] More recently, we have successfully synthesized vertically aligned carbon nanotubes co-doped with N and B (VA-BCN) and demonstrated a significantly improved electrocatalytic activity toward the ORR, with respect to CNTs doped with either N or B, only due to a synergetic effect arising from the N and B co-doping. [15] However, most of the reported carbon-based ORR electrocatalysts (particularly, heteroatom-doped nanotubes and graphene) were produced by chemical vapor-deposition (CVD) processes involving vacuum-based elaborate and careful fabrication, which are often too tedious and too expensive for mass production. As demonstrated in this study, therefore, it is of great importance to develop a facile approach to BCN graphene as low-cost and efficient ORR electrocatalysts. The recent availability of solution-exfoliated graphite oxide (GO) [16] allows the mass production of graphene and derivatives by conventional physicochemical treatments of GO.Herein, we have developed a facile approach to metalfree BCN graphene of tunable B/N co-doping levels as efficient...

Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

“…This is thus considered as one crucial factor for ORR activity enhancement by B-N-codoping. 93 In a similar approach, with varied N-and B-sources during thermal treatment of graphene oxide, Woo et al have presented a work supporting the previous results discussed here. Also their B-N-codoped graphene has proven itself as a good ORR catalyst, even under acidic conditions.…”

Templated synthesis of nitrogen-doped graphene-like carbon materials using spent montmorillonite

“…The higher-order peak appeared at 2700 cm À1 and a small broad peak at 2910 cm À1 were also observed, which can be assigned to a combination of D + D and D + G bands, respectively. 30 Both the intensity and shape of the two peaks were quite similar for the obtained carbon composites.…”

Boron Nitride Nanosheets for Metal Protection

“…Carbon and oxygen impurities are often present in BN crystals [16,37] and carbon doping can form boron carbide nitride which has been found to be efficient in oxygen reduction. [38,39] Nevertheless, the lower anodic current from the BN+Cu foil in aerated solution and the excellent anti-oxidation performance in air suggests that the oxygen reduction by the BN nanosheet does not enhance the formation of Cu 2 O on the underlying Cu surface. …”