Oxygen Evolution on Metal‐oxy‐hydroxides: Beneficial Role of Mixing Fe, Co, Ni Explained via Bifunctional Edge/acceptor Route

Abstract

Oxygen evolution reaction (OER) via mixed metal oxy hydroxides [M(O)(OH)] may take place on a large variety of possible active sites on the actual catalyst. A single site computational description assumes a 4‐step electrochemical mechanism with coupled H+/e− transfers between 4 intermediates (M‐*, M‐OH, M=O, M‐OOH). We also consider bifunctional routes, in which an unstable M‐OOH species converts via a proton shuttling pathway to a thermodynamically more favourable bare M‐* site, O2 and a hydrogenated acceptor site; the acceptor site takes up the proton forming a hydrogenated acceptor site after recombination with an electron from the catalyst material. Here, we combine pure metal γ‐M(O)(OH) edge sites (M=Fe, Co, Ni) with as proton‐acceptor sites different threefold coordinated oxygens on β‐(M,M’)(O)(OH) terraces (M,M’=Fe, Co, Ni). The acceptor sites on these terraces have of a M’2MO motif. Our combinatorial study results in a ranking of the bifunctional OER activity on a 3D‐volcano plot. By studying various bi‐ and tri‐metallic oxy hydroxide combinations, we show that their excellent experimental OER activity results from bifunctionality and provide a roadmap to construct innovative low overpotential OER catalysts.

From absolute potentials to a generalized computational standard hydrogen electrode for aqueous and non-aqueous solvents

“…The prediction of redox potentials using quantum-chemical calculations is central for understanding mechanisms and developing materials for electro-synthesis, 1,2 energy storage [3][4][5][6][7][8] and energy conversion. [9][10][11][12][13][14][15][16] Experimentally, these reactions are typically performed in water but non-aqueous solvents and ionic liquids are also far from uncommon. 1,[17][18][19][20] Owing to the importance of these applications, several computational protocols for the prediction of redox potentials have been developed over the last decades.…”

Key activity descriptors of nickel-iron oxygen evolution electrocatalysts in the presence of alkali metal cations

“…The catalytic site in the Ni-Fe catalysts has been characterized using in situ XAS, where several studies reveal contradicting information regarding the impact of Fe on the redox-activity of the Ni-site [20][21][22][23][24][25][26][27] . According to several DFT studies, the Fe-site plays a significant role as a low overpotential-site in the bimetallic Ni-Fe active site and provides optimal adsorption energies for the OER intermediates [28][29][30][31] , which is also supported by experiments 32 . In addition, Fe at coordinatively unsaturated sites such as edge sites or defect sites are predicted as more reactive [33][34][35] .…”

“…21) 31,[33][34][35]60 . Figure 5 shows the variation in these properties for the Fe-doped version of a γ-Ni(Fe)OOH(100) surface, often employed as a model for the catalytic behavior of Ni-Fe catalysts 28,30 . The maximum value in the surface electrostatic potential, V S,max , at the Ni site gives a measure of the electrostatic contribution to the local Lewis acidity of the metal site, whereas the minimum of the surface local electron attachment energy, E S,min , reflects the charge-transfer capacity of this site.…”

“…Based on our previous knowledge, the cation should not be modifying the catalytic activity of Ni(Fe)OOH significantly, however, below we will more carefully evaluate the catalytic activity using a set of local reactivity properties that correlate with the Lewis basicity/acidity of a metal site. The OER reaction path has recently been shown to pass through a bifunctional mechanism relying on the cooperation between a neighboring Ni–O Lewis acid-base pair 30 . This justifies that improved information of the reactivity of the Ni(Fe)OOH surface can be obtained by estimations of the local Lewis acidity and basicity of Ni, Fe and O lattice sites as a function of the intercalating cation.…”

Theoretical Study on the Structures of Single-Atom M (M=Fe, Co and Ni) Adsorption Outside and Inside the Defect Carbon Nanotubes

“…Moreover, once the defects formed, it is generally di cult to removed, eg., the recovery of the CNTs from the SW defect needs to overcome a very high barrier to ca 6eV [9]. We all know that Fe, Co and Ni nanocrystals have been used for organic pollutant removal due to their low cost and high catalytic activity [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Liu and coworkers report that the defect-rich Pt-M (M = Fe, Co, Ni) ultrathin nanowires can be used as electrode to enhance methanol electrooxidation.Fu et al study that PtM (M = Fe, Co, Ni) bimetallic nanoclusterscan be used as active and methanol-tolerant to enhance catalytic performances for the reactions of oxygen reduction.…”