Boron‐Doped Carbon Nanotubes as Metal‐Free Electrocatalysts for the Oxygen Reduction Reaction

Abstract

Fuel cells are clean, sustainable energy conversion devices for power generation, and they most commonly use platinum as the electrocatalyst. [1] However, Pt-based catalysts suffer from very limited reserves, high cost, and inactivation by CO poisoning; these are major obstacles that fuel cells have to overcome for commercialization. [1][2][3][4][5][6] Thus, exploring nonprecious metal or even metal-free catalysts to rival platinum in activity and durability is absolutely crucial, with a potentially revolutionary impact on fuel-cell technologies. Very recently, metal-free PEDOT [6] and nitrogen-doped carbon nanotubes (NCNTs) [7,8] have shown a striking electrocatalytic performance for the oxygen reduction reaction (ORR). These breakthroughs have activated an exciting field for exploring the advanced metal-free electrocatalysts and understanding the related mechanism.As one of the most important carbon nanostructures, carbon-based nanotubes have been widely studied as the support of electrocatalysts for fuel cells in recent years. [9][10][11][12] Recent progress involving doping carbon nanotubes (CNTs) with electron-rich nitrogen to transform CNTs into superb metal-free electrocatalysts for the ORR [7,8] has motivated our curiosity to examine the corresponding performance of its counterpart by doping CNTs with electron-deficient boron. Intuitively, the adsorption of O 2 on boron dopant should be quite easy owing to the large difference of electronegativity between boron and oxygen, which is the precondition for the subsequent O 2 dissociation. In this study, BCNTs with tunable boron content of 0-2.24 atom % were synthesized. The ORR onset and peak potentials shift positively and the current density increases noticeably with increasing boron content, indicating a strong dependence of the ORR performance on boron content. Moreover, the origin of the electrocatalytic activity of BCNTs including the role of the boron dopant has been revealed by density functional theory (DFT) calculations. The experimental and theoretical results provide a new strategy to explore carbon-based metal-free electrocatalysts that are significant to the development of fuel cells.Using chemical vapor deposition (CVD) with benzene, triphenylborane (TPB), and ferrocene as precursors and catalyst, BCNTs were synthesized with tunable boron content of 0-2.24 at % by using different TPB concentrations. BCNTs with boron content of 0.86, 1.33, and 2.24 at %, as determined by X-ray photoelectron spectroscopy (XPS), were denoted as B 1 CNTs, B 2 CNTs, and B 3 CNTs, respectively (Supporting Information, S1.

Carbon catalysts for electrochemical hydrogen peroxide production in acidic media

“…Among the important factors that influence the selectivity of carbon-based catalysts are the transition metal content [29] and the presence of surface functionalities (primarily N- [30,31], B [32], P [33] and S-containing [34,35] surface groups). Surface "defects" [36], particularly the edges [37,38] been reported to play a significant role.…”

Boron-doped graphene as active electrocatalyst for oxygen reduction reaction at a fuel-cell cathode

“…The existence of this end-on adsorbed O 2 species is crucial to trigger the associative ORR path which we consider to be the reason for the excellent performance of B-doped graphene as an electrocatalyst for this reaction [10,11,12].…”

Communication: Towards catalytic nitric oxide reduction via oligomerization on boron doped graphene

“…The importance of the latter O 2 desorption channel is because it is spin conserving as the peroxo intermediate also represents a singlet state. This channel would dominate on pristine graphene, however, the boron doping is understood to offer spin catalysis 25,26 rendering access to the 3 O 2 ground state upon dissociation. Interestingly, it is the high entropy of the irreversible N 2 O evolution channel which promotes the formation of graphene oxide, while it is the enthalpic instability of this graphene oxide which renders the direct N 2 + O 2 evolution channel, via the cis six member ring, competitive.…”