Creating Highly Active Atomic Layer Deposited NiO Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Atomic layer deposition (ALD) provides a promising route for depositing uniform thin coatings of electrocatalysts useful in many technologies, including the splitting of water. For materials such as NiO x that readily form hydrous oxides, however, the smooth, compact films deposited by ALD may result in higher overpotentials due to low catalyst surface area compared to other deposition methods. Here, the use of ALD–NiO thin films as oxygen evolution reaction (OER) electrocatalysts is explored. Thin films of crystalline ALD­–NiO are deposited and OER activity is tested using cyclic voltammetry (CV). Fe incorporated from the electrolyte can increase the activity of NiO, and it is shown that the turnover frequency (TOF) increases tenfold by going from an Fe‐poor to Fe‐rich KOH electrolyte. Applying a potential exfoliates the NiO, increasing the number of electrochemically accessible Ni sites. Interestingly, by X‐ray photoelectron spectroscopy (XPS) and CV, it is found that an Fe‐rich electrolyte reduces the amount of restructuring and oxidation is found. It is shown that a high surface area, high TOF catalyst may be created by using a two‐step process in which the sample is sequentially conditioned in Fe‐poor then Fe‐rich KOH. This work highlights the importance of pretreatment on catalytic activity for compact NiO films deposited by ALD.

Transition Metal-Modified Zirconium Phosphate Electrocatalysts for the Oxygen Evolution Reaction

“…On the other hand, the Fe(III)-intercalated sample, Figure 5A shows the Fe 2p3/2 peak at 711.6 eV, which is more consistent with previously-reported values expected for Fe(III) oxides, which generally exhibit the Fe 2p3/2 peak between 710.6 and 711.2 eV [47]. Deconvolution of the XPS spectra for Co(II) and Ni(II) is challenging due to the small shifts in the binding energy for the (II) and (III) metal oxidation states and the broad satellite peaks [49,50]. For the Co(II) sample, Figure 6A shows a Co 2p XPS spectrum with 2p3/2 and 2p1/2 peaks with characteristic satellite peaks, similar to those seen in other cobalt-based zirconium phosphate catalysts, but at higher binding energies, suggesting a partial oxidation of the Co species, containing both Co(II) and Co(III) characteristics [51].…”

“…For the Ni(II)-ZrP, Figure 6A shows a Ni 2p XPS spectrum with 2p3/2 and 2p1/2 peaks with satellite peaks, as well. The positions of the 2p3/2 and 2p1/2 peaks lie in between that of nickel oxide and nickel phosphate potentially elucidating that Ni cations are strongly interacting with both oxygen and phosphorus atoms in the ZrP [50,52]. Figure 6B shows the Zr 3d5/2 and 3d3/2 peaks and the P 2s peak for both intercalated and adsorbed samples, for the 10:1 Fe(II)-ZrP sample.…”

“…The presence of this polarization on the Zr and P atoms is more pronounced on the metal-adsorbed ZrP samples because the metal concentration on the surface of ZrP is higher than the metal-intercalated ZrP and, hence, the surface sensitivity of XPS can detect this binding energy shift. Deconvolution of the XPS spectra for Co(II) and Ni(II) is challenging due to the small shifts in the binding energy for the (II) and (III) metal oxidation states and the broad satellite peaks [49,50]. For the Co(II) sample, Figure 6A shows a Co 2p XPS spectrum with 2p 3/2 and 2p 1/2 peaks with characteristic satellite peaks, similar to those seen in other cobalt-based zirconium phosphate catalysts, but at higher binding energies, suggesting a partial oxidation of the Co species, containing both Co(II) and Co(III) characteristics [51].…”

All‐In‐One Perovskite Catalyst: Smart Controls of Architecture and Composition toward Enhanced Oxygen/Hydrogen Evolution Reactions

“…[5][6][7][8][9][10] In terms of achieving the best performances, the HER is usually carried out in an acidic environment while the OER in an alkaline condition. [5][6][7][8][9][10] In terms of achieving the best performances, the HER is usually carried out in an acidic environment while the OER in an alkaline condition.…”

“…[5][6][7][8][9][10] In terms of achieving the best performances, the HER is usually carried out in an acidic environment while the OER in an alkaline condition. [5][6][7][8][9][10][14][15][16][17][18] As a result, perovskites are being spotlighted as promising candidates due to their favorable compositional flexibility and good stability in a wide range of electrochemical window, thus enabling easy modification of their catalytic properties. In this context, a bifunctional electrocatalyst with high activities for both the OER and HER in an identical condition is desired.…”