Nitrogen‐Doped Carbon Activated in Situ by Embedded Nickel through the Mott–Schottky Effect for the Oxygen Reduction Reaction

Abstract

The development of low-cost non-precious-metal electrocatalysts with high activity and stability in the oxygen reduction reaction (ORR) remains a great challenge. Heteroatom-doped carbon materials are receiving increased attention in research as effective catalysts. However, the uncontrolled doping of heteroatoms into a carbon matrix tends to inhibit the activity of a catalyst. Here, the in situ activation of a uniquely structured nitrogen-doped carbon/Ni composite catalyst for the ORR is demonstrated. This well-designed catalyst is composed of a nitrogen-doped carbon shell and embedded metallic nickel. The embedded Ni nanoparticles, dispersed on stable alumina with a high specific surface area for protecting them from agglomeration and in an unambiguous composite structure, are electron-donating and are shielded by the nitrogen-doped carbon from oxidation/dissolution in harsh environments. The electronic structure of the nitrogen-doped carbon shell is modulated by the transfer of electrons at the interface of nitrogen-doped carbon-Ni heterojunctions owing to the Mott-Schottky effect. The electrochemically active surface area result implies that the active sites do not relate to Ni directly and the enhanced catalytic activity mainly arises from the modulation of nitrogen-doped carbon by nickel. XPS and theoretical calculations suggest that the donated electrons are transferred to pyridinic N primarily, which ought to enhance the catalytic activity intrinsically. Benefiting from these transferred electrons, the half-wave potential of the nitrogen-doped carbon/Ni composite catalyst is 94 mV positively shifted compared to the Ni-free sample.

Effect of Additives on the Foam Behavior of Aviation Coolants: Tendency, Stability, and Defoaming

“…The surface tension of GA solution reduces linearly with the glycol volume fraction. 37 The surface tension values of AC-2 and AC-3 are 53.1 and 53.2 mN/m, respectively, which are similar to that of 65% GA solution, indicating that the additives added in AC-2 and AC-3 have little effect on the surface tension. However, the surface tension of AC-1 (36.5 mN/m) and AC-4 (39.4 mN/m) is far below that of 65% GA solution (54.1 mN/m), revealing that the surfactants are added as additive, which can lower the solution surface tension effectively and promote foam formation.…”

Ternary Heterostructural Pt/CNx/Ni as a Supercatalyst for Oxygen Reduction

“…In previous work, we have demonstrated the charge transfer at the interface of CN x /Ni heterojunction because of the different Fermi levels of Ni and CN x matrix (Fu et al., 2014, Chen et al., 2017). The CN x layer is electron-rich after accepting electrons donated from Ni (see Figure S6).…”

Precious Metal-Free Nickel Nitride Catalyst for the Oxygen Reduction Reaction

“…[51][52][53] Nickel nitrogen-doped carbon (Ni-NC) type catalysts have also demonstrated good ORR performance, but they cannot be directly compared with this work due to their high surface area and the contributions of the NC support. 54,55 In alkaline electrolyte, nickel nitride shows similar activity with an onset at 0.68 V vs RHE but has a lower mass transport limited current density of 4 mA/cm 2 , as well as a slower onset with a halfwave potential of 0.42 V vs RHE. This difference in activity is reflected in the Tafel slopes: 89.7 mV/decade in acid compared to 175 mV/decade in alkaline (Fig.…”

“…Second, after discovery of a promising material system, the number of active sites can be increased through nanostructuring and supporting the catalyst on a high surface area material such as N-doped carbon. 54,55…”