The Role of Aluminum in Promoting Ni–Fe–OOH Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Nickel–iron oxyhydroxide (Ni–Fe–OOH) catalysts have been widely studied for their high activity for the oxygen evolution reaction (OER). Here we demonstrate improved OER activity through incorporation of a third cation, aluminum. Atomic layer deposition (ALD) was used to deposit thin films of nickel oxide (Ni–O) and nickel–aluminum oxide (Ni–Al–O) to measure activity for the OER. Electrochemical preconditioning of the oxide films led to the formation of the OER-active oxyhydroxide catalysts. For Ni–Al–O films, electrochemical preconditioning resulted in aluminum dissolution until a stable composition at a Ni:Al ratio of 9:1 was reached. Because iron can be incorporated into the films from the solution, compositional effects of iron were studied by controlling the iron impurity level in the electrolyte. Turnover frequencies (TOFs) were determined for each catalyst, and it was found that the highest performing electrocatalysts were the films containing nickel, aluminum, and iron, confirming that aluminum exerts a promotion effect on nickel oxyhydroxide catalysts. Studies showed that unlike the Ni–Fe–OOH films, for which the TOF had very little thickness dependence, the activity of Ni–Al–Fe–OOH catalysts was dependent on thickness. This effect may arise from morphological changes in the catalyst film that modulate the density of the active site with thickness. For the thinnest films, aluminum doping improved the TOF of Ni–Fe–OOH catalysts by over 3-fold.

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

“…The lack of these atomic-scale details has, in turn, made it highly challenging to choose appropriate models for DFT-based mechanistic studies 4,38,41 . Hence, a variety of structures have been employed in the modeling, including those that resemble as-synthesized precursor phases 37 , NiO 38 , twodimensional single layer (oxy)hydroxides 35,39 , β-MOOH analogs 4,[10][11][12]42 , and γ-NiOOH analogs 33,40,[43][44][45] with or without Fe dopants. Although significant efforts have been made to explain the high activity of MFe LDHs, the diversity of studies suggests that large uncertainties exist concerning the relationship between the active site structure and the catalytic mechanism.…”

Origin of Enhanced Water Oxidation Activity in an Iridium Single Atom Catalyst

“…1A). For NiFe, we used a widely adopted -NiFeOOH bulk model with interlaced and solvated K + cations and protons, since 1 M KOH was used as electrolyte in the experiment (See SI for Computational Details) (18,30,31). Out of a large number of tested cases, only two possibilities had significant negative free energy of Ir doping (Fig.…”

“…To complete our analysis of Ir0.1/Ni9Fe SAC system, we evaluated theoretical OER overpotentials (see Computational Details in SI) of the obtained stable systems utilizing Ir at edge-sites, subsurface and as single-atom near Fe-sites (adapted from Au single-atom study (37)) in the (100) surface of NiFe labelled as NiFeIr, and octahedral NiFeIr SAC anchored at the NiFe basal planes [(001) facet]. These are compared to (110) surface of rutile IrO2 and to Fe-site in NiFe (100) surface obtained previously (31). First, we show that the calculated GOOH to GOH scaling (Fig.…”

Well‐Monodispersed Iron‐Doped InOOH Nanoparticles with Enhanced Activity for Oxygen Evolution

“…[10][11][12] Transition metal-based oxyhydroxides are attractive electrocatalyst candidates due to their water oxidation activity in alkaline medium and low cost, such as FeOOH, CoOOH, NiOOH, VOOH, CrOOH and so on. [13][14][15] However, InOOH, a typical oxyhydroxide, which has been reported the photocatalytic activities in the organic contaminants degradation and water splitting, nevertheless, has received no attention among electrocatalysts towards OER. [16,17] Generally, because of the disadvantage of limited electronic configuration, the catalytic efficiency of monometallic oxyhydroxide is still below expectation.…”

“…The design and synthesis of OER catalysts based of non‐precious metals has become a research focus in the field of energy storage and conversion . Transition metal‐based oxyhydroxides are attractive electrocatalyst candidates due to their water oxidation activity in alkaline medium and low cost, such as FeOOH, CoOOH, NiOOH, VOOH, CrOOH and so on . However, InOOH, a typical oxyhydroxide, which has been reported the photocatalytic activities in the organic contaminants degradation and water splitting, nevertheless, has received no attention among electrocatalysts towards OER .…”