Core/Shell NiFe Nanoalloy with a Discrete N‐doped Graphitic Carbon Cover for Enhanced Water Oxidation

Abstract

Developing highly efficient and earth‐abundant electrocatalysts for the oxygen evolution reaction (OER) is critical in overall water splitting technology. Among all transition‐metal‐based materials, NiFe‐based electrocatalysts have been regarded as the most promising substitute to commercial noble metals in alkaline conditions. To overcome their leaching problem and improve intrinsic stability without compromising activity, we report a NiFe alloy covered with a discrete N‐doped graphitic shell for the OER. The alloy core@discrete graphitic shell structure exhibits enhanced OER activity and stability with a low onset potential of 1.48 V, reduced overpotential of 320 mV@10 mA cm−1, and small Tafel slope value of 41 mV dec−1, which is superior to Ir/C. It is believed that the nitrogen doping, a discrete graphitic shell, and a mesoporous structure work in harmony to enhance the OER performance.

One‐Step Synthesis of NiFe Layered Double Hydroxide Nanosheet Array/N‐Doped Graphite Foam Electrodes for Oxygen Evolution Reactions

“…When coated by NiFe LDH, NiFe LDH/NGF-4 shows a much reduced onset overpotential of 0.233 V, indicating the better OER catalytic activity which is superior to IrO 2 /NGF electrode (0.240 V) and the reported NiFe based OER catalysts (Table S1). [23,32,47,[56][57][58][59] Tafel slopes of NiFe LDH/NGF-4, NGF and IrO 2 /NGF electrodes were calculated to be 59.4, 127.5, and 62.5 mV dec À 1 , respectively, confirming the better catalytic activity of NiFe LDH/NGF-4.…”

“…has been widely explored . Moreover, the introduction of nitrogen dopants in these nanocarbons has been demonstrated as an efficient mean to further improve the dispersion of LDHs and the charge transfer because of the created anchoring sites and enhanced electron‐donor property, respectively …”

“…[28][29][30][31] Moreover, the introduction of nitro-gen dopants in these nanocarbons has been demonstrated as an efficient mean to further improve the dispersion of LDHs and the charge transfer because of the created anchoring sites and enhanced electron-donor property, respectively. [32][33][34][35] The mass transport and diffusion issue during OER should also be considered since it occurs at the triple-phase boundary regions. [36][37][38] To enhance the diffusion of liquid reactants and gas products, directly fabricating the active species with three dimensional (3D) architecture on free-standing conductive substrates as integrated electrodes has been explored.…”

Recent Progress on NiFe‐Based Electrocatalysts for Alkaline Oxygen Evolution

“…At the same time, the OER performance can be efficiently excited by the changed electronic structure and the optimal adsorption strength of reaction intermediates. [ 43,44 ] For example, Wang’s group formulated a route to synthesize core/shell NiFe nanoalloy containing N‐doped graphite shell (Figure 2c), [ 45 ] which required an overpotential of 320 mV to reach 10 mA cm −2 in 1.0 m KOH. The synthetic discrete graphite shells play a role in limiting the NiFe alloy core and generating more active sites.…”

“…Reproduced with permission. [ 45 ] Copyright 2018, Wiley‐VCH. d) HRTEM images of FeNi@Gr‐900 and corresponding Schematic illustration.…”