Mechanisms of the Oxygen Evolution Reaction on NiFe₂O₄ and CoFe₂O₄ Inverse-Spinel Oxides

Abstract

Spinel ferrites, especially Nickel ferrite, NiFe 2 O 4 , and Cobalt ferrite, CoFe 2 O 4 , are efficient and promising anode catalyst materials in the field of electrochemical water splitting. Using density functional theory, we extensively investigate and quantitatively model the mechanism and energetics of the oxygen evolution reaction (OER) on the (001) facets of their inverse-spinel structure, thought as the most abundant orientations under reaction conditions. We catalogue a wide set of intermediates and mechanistic pathways, including the lattice oxygen mechanism (LOM) and adsorbate evolution mechanism (AEM), along with critical (rate-determining) O–O bond formation barriers and transition-state structures. In the case of NiFe 2 O 4 , we predict a Fe-site-assisted LOM pathway as the preferred OER mechanism, with a barrier (Δ G ⧧ ) of 0.84 eV at U = 1.63 V versus SHE and a turnover frequency (TOF) of 0.26 s –1 at 0.40 V overpotential. In the case of CoFe 2 O 4 , we find that a Fe-site-assisted LOM pathway (Δ G ⧧ = 0.79 eV at U = 1.63 V vs SHE, TOF = 1.81 s –1 at 0.40 V overpotential) and a Co-site-assisted AEM pathway (Δ G ⧧ = 0.79 eV at bias > U = 1.34 V vs SHE, TOF = 1.81 s –1 at bias >1.34 V) could both play a role, suggesting a coexistence of active sites, in keeping with experimental observations. The computationally predicted turnover frequencies exhibit a fair agreement with experimentally reported data and suggest CoFe 2 O 4 as a more promising OER catalyst than NiFe 2 O 4 in the pristine case, especially for the Co-site-assisted OER pathway, and may offer a basis for further progress and optimization.

Improving the Oxygen Evolution Reaction on Fe3O4(001) with Single-Atom Catalysts

“… 38 , 68 In the case of Co-doped systems, the overpotential values for the incorporated in or deposited on species (0.36 and 0.35 V, respectively) are very close to the value of 0.38 V that was computed for the CoFe 2 O 4 (001) surface. 68 These new results prove that the same performance toward OER can be obtained by introducing a limited quantity of Co or Ni on the Fe 3 O 4 surface rather than by using Co/Fe or Ni/Fe mixed oxides and, thus, provide experimentalists a clear and practical way to cut the catalyst cost.…”

“…As an approximate description of the presence of the solvent, one dissociated water molecule was adsorbed on the slabs: ,, the OH fragment was adsorbed on an exposed fivefold coordinated Fe Oct III (in the case of clean DBT, Ti in @DBT, and Co in @DBT, left panels in Figure b) or on an adatom (in the case of Co ad @SCV, Ni ad @SCV, and Cu ad @SCV, right panels in Figure b), whereas the H fragment was adsorbed on an exposed surface oxygen nearby. The adsorption energy ( E Ads ) for the dissociated water molecule was calculated as follows E Ads = E total − ( E surface + E H 2 O ) where E total is the total energy of the whole system (surface and adsorbed water), E surface is the energy of the isolated Fe 3 O 4 (001) surface, and E H 2 O is the energy of one isolated water molecule.…”

Adjacent Fe Site boosts electrocatalytic oxygen evolution at Co site in single-atom-catalyst through a dual-metal-site design

“…16 Thus, decoupling the scaling relation of the intermediate species through the surface structure design on the catalyst is considered to be the best strategy for the OER. [17][18][19] However, the development of OER catalysts remains a challenge due to the high overpotentials required to drive the multi-electron and multi-proton redox reaction, which also accelerate the destruction of the highly active surface structures. It has been reported that the surface coverage of the intermediate species strongly affects the reaction kinetics at a low overpotential.…”

“…16 Thus, decoupling the scaling relation of the intermediate species through the surface structure design on the catalyst is considered to be the best strategy for the OER. 17–19…”

Insights into the Electrocatalytic Oxygen Evolution Reaction and Photocatalytic Methylene Blue Degradation of Mixed Spinel NixCu1–xFe2O4 Nanocomposites Anchored at Sulfur-Doped g-C3N4

“…In the 21st century, energy and environmental crises are prominently noticeable and rectifiable due to the acceleration of industrialization and urbanization in and around the world. − In particular, researchers are focused on developing electrocatalytic and/or photocatalytic active nanomaterials for water splitting as well as for photodegradation of organic pollutants, which are challenging but demanding research topics in this scenario. − Thereby, the oxygen evolution process has drawn a lot of interest since it can produce incredibly clean hydrogen through water electrolysis, which can aid in resolving the existing issues. , The multistep four-electron transfer mechanism, however, which results in hysteretic reaction conditions, is the main bottleneck for oxygen evolution reaction (OER). To enhance the reaction kinetics, high-performance electrocatalysts such as RuO 2 and IrO 2 have been utilized.…”