Atmospheric-Pressure Plasma Jet-Induced Ultrafast Construction of an Ultrathin Nonstoichiometric Nickel Oxide Layer with Mixed Ni³⁺/Ni²⁺ Ions and Rich Oxygen Defects as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Abstract

An approach, i.e., atmospheric-pressure nonequilibrium oxygen plasma jet technology, has been reported for the first time to in situ prepare ultrathin nonstoichiometric nickel oxide layers with mixed Ni 3+ /Ni 2+ ions and rich oxygen defects on the surface of three-dimensional (3D) nickel foams (APPJ-Ni x O y /NFs). It depends on the bombardment of the highly reactive energetic species (including O, OH • , O 2 + , and e) with the NF to form the oxide layer in an ultrafast way. The specific feature of the plasma technology gives rise to the simultaneous formation of mixed Ni 3+ /Ni 2+ ions and rich oxygen defects in the APPJ-Ni x O y /NFs. Specifically, for the APPJ-Ni x O y /NFs formed in a short time of 5 min, they show remarkably high catalytic activities and excellent stability for the oxygen evolution reaction (OER). They only need an onset potential of 1.490 V and an overpotential of 355 mV to drive a current density of 10 mA cm −2 . They also exhibit faster reaction kinetics and a lower Tafel slope (88 mV dec −1 ). The presence of mixed Ni 3+ /Ni 2+ ions and rich oxygen defects plays an important role in the high catalytic activities of the APPJ-Ni x O y / NFs. Density functional theory (DFT) calculations indicate that the heterojunction between the Ni x O y layer and the NF greatly reduces the U L (OER) value, which also contributes to the high catalytic activities of the APPJ-Ni x O y /NFs. The work reported here provides a potential approach to fabricating transition metal oxide layers with enhanced catalytic activities for overall water splitting.

Cold Plasma Synthesis and Testing of NiOX-Based Thin-Film Catalysts for CO2 Methanation

“…However, the latter case is unlikely because no other diffraction peaks for the Ni fcc structure can be seen here [40,41]. Meanwhile, at the 44.2 • position, a diffraction peak for NiO is also predicted [42]. The presence of NiO in the film is confirmed by weak reflection at 37.3 • [43].…”

“…If we regenerate the spent catalyst film, as it was done with the air-NiO X film (Figure 4b), the original molecular structure of the film is practically reconstructed, which is accompanied by a return to the initial catalytic activity in the methanation process. These interesting findings require further study to determine the role of Ni 3+ in the catalytic mechanism, which can be quite complex, for example, through the interaction of Ni 3+ with Ni 2+ [42], as well as to search for the possibility of ensuring the stability of the catalyst, for example by adding appropriate promoters [53,54].…”

Plasma modified and tailored defective electrocatalysts for water electrolysis and hydrogen fuel cells

“…This plasma‐based method can synthesize bimetallic hydroxide‐oxide nano‐interfaced materials. Zhang et al have proposed a method using nonequilibrium O 2 plasma jets at atmospheric pressure to synthesize thin nonstoichiometric nickel oxide layers with Ni 2+ /Ni 3+ and abundant oxygen defects supported by Ni foams 115 . Rapid formation of the oxide layer arises from bombardment by energetic species including O, •OH, O 2 + , and e − in the oxygen plasma.…”

“…Zhang et al have proposed a method using nonequilibrium O 2 plasma jets at atmospheric pressure to synthesize thin nonstoichiometric nickel oxide layers with Ni 2+ /Ni 3+ and abundant oxygen defects supported by Ni foams. 115…”

Hybrid transition metal (V, Fe, and Co) oxide/sulfide catalysts for highly efficient overall water splitting

“…This made the process of forming M–OH easier to occur, thus reducing the Gibbs free energy of the OER. 12 In the XPS spectrum of Fe 2p (Fig. 2c), for Fe oxide and sulfide, the peaks at 711.4 and 723.4 eV represented the characteristic Fe 2p 1/2 and 2p 3/2 of Fe 3+ , and the peaks at 707.4 and 715.3 eV indicated that Fe 2+ also existed.…”