A simple and efficient method was developed to prepare a copper−carbon (Cu−C) catalyst with high oxygen reduction reaction (ORR) activity via direct pyrolysis of a mixture of metal salts (Cu(NO 3 ) 2 •3H 2 O and Zn(CH 3 COO) 2 ) and 1,3,5-benzenetricarbocylic acid at 1010 °C under a N 2 stream. It is found that the Cu−C catalyst exhibits superior catalytic activity toward ORR with a half-wave potential of 0.81 V and a four-electron transfer pathway in 0.1 M KOH electrolyte. Generally, it is known that N plays an important role for the high ORR catalytic activities of nonprecious metaldoped carbon materials. Herein, we demonstrate that N is not required for the superior catalytic activity of Cu−C materials. Both the Cu particles and the embedded Cu atoms in the carbon substrate are suggested to provide the ORR active sites. In addition, despite the fact that the Zn is removed during the pyrolysis, the adding of Zn salt in the precursor is important for the enhanced catalytic activity. The evaporation of Zn during the pyrolysis results in the large surface area of the catalyst, which is beneficial to the mass transfer during the catalytic process. Moreover, a large number of carbon defects can be created via the removal of Zn atoms that facilitated the ORR.

Transition metal-nitrogen-carbon (MÀ NÀ C) materials have received extensive attention as promising catalysts for oxygen reduction reaction (ORR). The surface morphology and the pore structure of the carbon supports have important effects on the ORR activity. Herein, metal-organic complexes were prepared via a simple NaOH-mediated method by the organometallic reaction of Fe 3 + /Co 2 + ions and benzimidazole in the presence of polyvinylpyrrolidone. Metal-organic complexes with either cuboid or cylindrical morphologies were obtained by modulating the initial ratio of Fe 3 + /Co 2 +. FeCo containing N-doped carbon catalysts (Fe x Co y À NÀ C) decorated with Fe x Co y nano-particles were then fabricated by a direct carbonization of the metal-organic complexes. Fe x Co y À NÀ C catalysts have hierarchical micro-/mesoporous structure and retain the morphologies of microcuboids and microcylinders of the metal-organic complexes precursors. The Fe 1 Co 7 À NÀ C exhibits promising catalytic activity with an onset potential of 0.967 V, a half-wave potential of 0.816 V, and a limiting current density of 4.86 mA cm À 2 in 0.1 M KOH. The ORR catalytic activity should be attributed to the FeCoÀ N x active sites and the encapsulated FeCo alloy nanoparticles activating the surrounding N-doped carbon layers.

It remains a challenge to develop an efficient and facile method to synthesize nonprecious metal electrocatalysts with controlled structure and desired properties. This study reports a two-step pyrolysis method plus acid leaching between the two pyrolysis stages to synthesize Fe-, S-, and N-doped carbon nanotubes (CNTs) with a controlled size as efficient electrocatalysts for the oxygen reduction reaction (ORR). The synthesis involves a first-step pyrolysis at 700 °C to form small-diameter CNTs, a subsequent acid-etching to remove the majority of the metal nanoparticles, and a second-step pyrolysis at 900 °C to improve the crystallinity but retain the small diameter of the CNTs. The method is proved to be effective in achieving a large specific surface area and stabilizing the S species of the catalyst. Owing to the synergistic effect between the S functionalities and Fe–N x sites, the high specific surface area, and the 3D interconnect network of small-diameter CNTs, the catalyst exhibits superior activity toward the ORR with a half-wave potential of 0.854 V and a limiting current density of 5.62 mA cm–2 in alkaline medium, better than those prepared by one-step pyrolysis and the commercial Pt/C. The present simple synthetic strategy for small-diameter CNTs may have potentials for diverse applications.

Transition metal and nitrogen co-doped carbon materials have been widely investigated as promising electrocatalysts for oxygen reduction reaction (ORR). Incorporating two different metals in N-doped carbon may synergistically improve the catalytic activity. Herein, Ni/Cu incorporated N-doped porous carbon materials (Ni 1-x Cu x -NÀ C) with different Ni/Cu ratios were prepared by a direct carbonization of the metal-organic complexes which were obtained via a NaOH-mediated organometallic reaction of metal ions and benzimidazole. It is found that the Ni/Cu ratio significantly alters the Ni 1-x Cu x particle sizes, the surface morphology, the specific surface area, and the pore structure of the catalysts, eventually affecting the ORR activities. Ni 0.7 Cu 0.3 -NÀ C exhibits the best ORR activity among the studied Ni 1-x Cu x -NÀ C catalysts with a half-wave potential of 0.783 V and a limiting current density of 4.85 mA cm À 2 in alkaline medium. Density functional theory calculations confirm that the synergistic effect of bimetallic Ni/Cu can optimize the adsorption/desorption features and promote the ORR catalytic activities.