In-situ structure and catalytic mechanism of NiFe and CoFe layered double hydroxides during oxygen evolution

Abstract

NiFe and CoFe (MFe) layered double hydroxides (LDHs) are among the most active electrocatalysts for the alkaline oxygen evolution reaction (OER). Herein, we combine electrochemical measurements, operando X-ray scattering and absorption spectroscopy, and density functional theory (DFT) calculations to elucidate the catalytically active phase, reaction center and the OER mechanism. We provide the first direct atomic-scale evidence that, under applied anodic potentials, MFe LDHs oxidize from as-prepared α-phases to activated γphases. The OER-active γ-phases are characterized by about 8% contraction of the lattice spacing and switching of the intercalated ions. DFT calculations reveal that the OER proceeds via a Mars van Krevelen mechanism. The flexible electronic structure of the surface Fe sites, and their synergy with nearest-neighbor M sites through formation of O-bridged Fe-M reaction centers, stabilize OER intermediates that are unfavorable on pure MM centers and single Fe sites, fundamentally accounting for the high catalytic activity of MFe LDHs.

Design and operando/in situ characterization of precious‐metal‐free electrocatalysts for alkaline water splitting

“…32,153 It is established that Fe incorporation plays a critical role for boosting the OER activity, especially in Ni-and Co-based electrocatalysts, because of the enhanced the density of active sites and rapid OH − adsorption and O 2 desorption during the OER process. [153][154][155] For example, Fe-doped NiSe/NF, Ni 3 S 2 /NF, and LaNiO 3 displayed higher OER activity in comparison with pristine materials. 151,156,157 Similarly, introducing Ni and Co cations into the host materials is also beneficial for improving the catalytic performance owing to the preferable reaction kinetics.…”

Engineering 2D Materials: A Viable Pathway for Improved Electrochemical Energy Storage

“…For example, Wang et al prepared graphene-like C 3 N 4 materials with high surface area (various edge and wrinkled structures) for a Zn-air battery, and reported a peak density up to 100 mW cm −2 . [174] By taking advantage of the ORR and OER of various 2D materials (e.g., LDHs and MOF materials), [175][176][177][178][179][180] along with the above discussed geometric point defects and edge-like structures, design of high-performance energy storage devices based on the promising catalysis can be highly expectable.…”

“…Although the structures and chemical compositions of many LDHs are complex, recent investigations on several LDHs by Strasser et al confirmed the critical role of chemical doping in regulating the catalysis. [175][176][177] It was found that additions of Fe species into Co and Ni based LDHs enhanced the OER activity significantly. [176,177] More recently, Strasser et al further investigated the relationship between the structure and catalytic mechanism of NiFe and CoFe LDHs (both have high activity on OER) at the atomic level.…”

“…[176,177] More recently, Strasser et al further investigated the relationship between the structure and catalytic mechanism of NiFe and CoFe LDHs (both have high activity on OER) at the atomic level. [175] It was revealed that Fe sites in NiFe and CoFe LDHs (high activity on OER) led to the formation of O bridged Fe-M reaction centers which stabilized OER intermediates (therefore improved the catalysis), which was unlikely the case on pure M-M (M: metal) centers and single Fe sites, suggesting the critical effect of the chemical doping in activating and promoting the catalysis. These results could guide the design and fabrication of LDH based catalysts for efficient Zn-air batteries, although significant efforts may still need to be made for additional engineering issues.…”

Genuine Active Species Generated from Fe3N Nanotube by Synergistic CoNi Doping for Boosted Oxygen Evolution Catalysis

“…Unlike those amorphous (oxyhyr)oxides, crystalline CoNi-FeOOH is evidenced in the post-OER CoNi-Fe 3 N, which confirms that CoNi co-incorporation is favorable for the orderly rearrangement of Fe atoms in Fe 3 N toward FeOOH. More importantly, compared with the common Fe/Co/Ni layered double hydroxides (LDH) [51] and oxides, [52] which can also undergo reconstruction during OER, the metallic CoNi-Fe 3 N can ensure the electronic conductivity for generated CoNi-FeOOH, which is highly important for efficient electrocatalysis.…”