Search

[Display omitted] • Hybrid of Co 3 W and WN enhances the catalytic activity for HER. • Synergistic effect of Co 3 W and WN enhances electrocatalytic performance for HER. • Hybrid of alloy and metal nitride can be high performance catalyst for HER. • Co 3 W-WN/rGO-1-800 in 0.1 M KOH has smaller overpotential at 60 mA/cm2 than Pt/C. Hydrogen, as the most environment-friendly fuel, is believed as the eventual energy for human beings. The produce, storage and transportation of hydrogen are crucial technologies for the large-scale applications of hydrogen. Electrolysis is one of the most feasible way to produce hydrogen despite the shortage of low-cost and high-performance catalysts. Developing high cost-effective non-precious metal-based electrocatalysts for hydrogen evolution reaction (HER) is crucial for the production of hydrogen. In this paper, reduced graphene oxide (rGO) supported cobalt-doped tungsten nitride (Co-WN/rGO), tungsten-cobalt alloy and tungsten nitride hybrid (Co 3 W-WN/rGO) were prepared by hydrothermal followed with nitridation treatment method. XRD, SEM and XPS tests show that the Co 3 W-WN hybrids are uniformly dispersed on the rGO support. HRTEM clearly proved the coexistence of Co 3 W and WN on rGO. Electrocatalytic performance tests of Co-WN/rGO and Co 3 W-WN/rGO show that the overpotential of Co 3 W-WN/rGO-1-800 catalyzed HER is lower than that of 20 wt% Pt/C in 0.1 M KOH solution at current density of 60 mA/cm2. In addition, in 0.5 M H 2 SO 4 solution, the overpotential of Co 3 W-WN/rGO-1-800 catalyzed HER is only 83 mV higher than that of the Pt/C catalyst at the current density of 300 mA/cm2. The high catalytic performance should be attributed to the synergistic effect between Co 3 W and WN. The results of the paper provide a novel strategy to design high performance transition metal-based catalysts for HER and give a new insight into the catalytic mechanism. [ABSTRACT FROM AUTHOR]

The encapsulated cementite changed the electron distribution state of surface layer CNT, which enhanced the catalytic activity for oxygen reduction reaction. [Display omitted] • N-doped CNT with cementite encapsulated was synthesized as a catalyst for ORR. • Encapsulated cementite changed the electron distribution of surface layer CNT. • The E 0 and E 1/2 of Fe 3 C@CNT catalyzed ORR is 60 mV higher than that of Pt/C. • Equal-potential circle theory is proposed to explain catalytic mechanism for ORR. Nonprecious-metal-based materials show great potential to be highly efficient catalysts for oxygen reduction reaction (ORR). There is still room for improvement in the performances of nonprecious-metal-based catalysts for ORR. In this paper, we investigated the catalytic performances of N-doped carbon nanotubes (CNTs) with encapsulated cementite (Fe 3 C@CNT) for ORR. The encapsulation structure was confirmed by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. The catalytic performances of Fe 3 C@CNT for ORR were investigated by cyclic voltammetry, linear sweep voltammetry, Tafel analysis, rotating disk electrode, and rotating ring-disk electrode tests. The results showed that both the onset potential and half-wave potential of Fe 3 C@CNT-catalyzed ORR were 60 mV higher than those of 20 wt% Pt/C catalyst. Fe 3 C@CNT catalyzed ORR mainly happened through a four-electron pathway. The long-time running stability of the Fe 3 C@CNT was also superior to that of the 20 wt% Pt/C catalyst. The eutectic layers between the CNTs and cementite enhanced the electron transfer from the inner-layer CNT to the surface-layer N-doped CNT. Calculations revealed that the iron and carbon in the cementite were in positive and negative electronic states, respectively. The encapsulated cementite promoted the formation of equipotential circles on the surface-layer CNT, which greatly enhanced the catalytic performance of the Fe 3 C@CNT for ORR. N-doped CNTs with encapsulated cementite show great potential to be high-performance catalysts for ORR. [ABSTRACT FROM AUTHOR]