Nickel Site Modification by High-Valence Doping: Effect of Tantalum Impurities on the Alkaline Water Electro-Oxidation by NiO Probed by Operando Raman Spectroscopy

Abstract

In an effort to support the large-scale implementation of clean hydrogen in industry and society, the electrolytic decomposition of water is considered a realistically enticing prospect, provided the guarantee of affordable and durable material components. Within alkaline systems, earth-abundant electrocatalysts could provide both these requirements. However, a continued exploration of the reactivity and the causes behind different behaviors in performance are necessary to guide optimization and design. In this paper, Ta-doped NiO thin films are prepared via DC magnetron sputtering (1–2–4 at % Ta) to demonstrate the effect of surface electronic modulation by non-3d elements on the catalysis of the oxygen evolution reaction (OER). Material properties of the catalysts are analyzed via Rutherford backscattering spectrometry, X-ray diffractometry, photoelectron spectroscopy, and Raman spectroscopy. Ta impurities are shown to be directly responsible for increasing the valence state of Ni sites and enhancing reaction kinetics, resulting in performance improvements of up to 64 mV at 10 mA cm –2 relative to pristine NiO. Particularly, we show that by applying operando Raman spectroscopy, Ta enhances the ability to create high-valence Ni in γ-NiOOH at a lower overpotential compared to the undoped sample. The lowered overpotentials of the OER can thus be attributed to the energetically less hindered advent of the creation of γ-NiOOH species on the pre-catalyst surface: a phenomenon otherwise unresolved through simple voltammetry.

Designing Ag@NiO as Air Electrode Catalysts with Synergistic Interface and Doping Engineering Strategies for High-Performance Lithium–Oxygen Batteries

“…It should be noted that the peak at 43.32° is slightly distracted toward lower angles after Ag-ion introduction, which shows that some Ag-ions have successfully adulterated into the NiO lattice in order to improve the lattice constant without changing the crystal structure of NiO . As shown in Figure b, the Raman peak at ∼500 cm –1 corresponds to the first-order phonon (1P) LO mode of NiO, and the next two peaks at ∼712 and ∼1060 cm –1 are due to the second-order phonon (2P) 2TO and 2LO vibration mode, respectively. − As we can see, the 1P peak is visibly broadened compared with the original NiO in the purple region, demonstrating that the introduction of the Ag heteroatom causes the decrease of the NiO crystallinity. It means that interface defects and high activation groups are produced, which is conducive to enhancing the catalytic activity of NiO .…”

Facilitating Reconstruction of the Heterointerface Electronic Structure by the Enriched Oxygen Vacancy for the Oxygen Evolution Reaction

“…As shown in Figure 4h,i, when ramped electrical bias potentials increased from 1.1 to 1.8 V (vs RHE), the intensity of the pairs of peaks stretching at 474 and 551 cm −1 , which belong to the Ni III −O bending and stretching vibrations of NiOOH, gradually appeared and was enhanced upon the electrode being immersed in an alkaline medium. 41 Additionally, a new vibrational mode is visible at ∼1400 cm −1 represented by the magnon mode (2 M), which originated from the antiferromagnetic super-exchange interactions between Ni cations when the electrolytic potential is above 1.3 V. 42 Furthermore, the apparent peaks at ∼1570 cm −1 starting from 1.1 V are inputs to the stretching mode of dissolved O 2 , highlighting the fleet kinetics of the transformation of oxygen intermediates into oxygen gas. 43 This fact illustrates that the OH − should be the first to approach the electrode surface and faster give rise to oxygen intermediates such as *OH and *O as the electrolytic potential ascent progressively rises under alkaline conditions.…”

Effects of Capping Agents on Shape, Stability, and Oxygen Evolution Reaction Activity of Copper Nanoparticles

“…Additionally computed for both capped and uncapped reaction media were the usual crystallite sizes of the nano-sized copper products. 1 The decreased crystallite size of copper nanoparticles in the reaction media including capping agents is probably caused by two main causes. As reported, 23 capping agents have been demonstrated to reduce Cu 2+ to Cu + , which may encourage the development of copper nanoparticle nuclei.…”

“…OER is consequently believed to be the bottleneck in water electrolyzers. [1][2][3] Additionally, metal-air batteries, regenerated fuel cells, and carbon dioxide electrolyzers utilize the oxygen evolution process in anodes. 4 Therefore, for these electrochemical energy devices, the development of efficient OER electro-catalysts is essential.…”