Tuning Coordination Geometry of Nickel Ketoiminates and Its Influence on Thermal Characteristics for Chemical Vapor Deposition of Nanostructured NiO Electrocatalysts

Abstract

Nickel-based nanostructured materials have gained widespread attention, particularly for energy-related applications. Employing chemical vapor deposition (CVD) for NiO necessitates suitable nickel precursors that are volatile and stable. Herein, we report the synthesis and characterization of a series of new nickel β-ketoiminato complexes with different aliphatic and etheric side chain substitutions, namely, bis­(4-(isopropylamino)-pent-3-en-2-onato)­nickel­(II) ([Ni­(ipki)2], 1), bis­(4-(2-methoxyethylamino)­pent-3-en-2-onato)­nickel­(II) ([Ni­(meki)2], 2), bis­(4-(2-ethoxyethylamino)­pent-3-en-2-onato)­nickel­(II) ([Ni­(eeki)2], 3), bis­(4-(3-methoxy-propylamino)-pent-3-en-2-onato)­nickel­(II) ([Ni­(mpki)2], 4), and bis­(4-(3-ethoxypropylamino)­pent-3-en-2-onato)­nickel­(II) ([Ni­(epki)2], 5). These compounds have been thoroughly characterized with regard to their purity and identity by means of nuclear magnetic resonance spectroscopy (NMR) and electron impact mass spectrometry (EI-MS). Contrary to other transition metal β-ketoiminates, the imino side chain strongly influences the structural geometry of the complexes, which was ascertained via single-crystal X-ray diffraction (XRD). As a result, the magnetic momenta of the molecules also differ significantly as evidenced by the magnetic susceptibility measurements employing Evan’s NMR method in solution. Thermal analysis revealed the suitability of these compounds as new class of precursors for CVD of Ni containing materials. As a representative precursor, compound 2 was evaluated for the CVD of NiO thin films on Si(100) and conductive glass substrates. The as-deposited nanostructured layers were stoichiometric and phase pure NiO as confirmed by XRD, Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA). X-ray photoelectron spectroscopy (XPS) indicated the formation of slightly oxygen-rich surfaces. The assessment of NiO films in electrocatalysis revealed promising activity for the oxygen evolution reactions (OER). The current densities of 10 mA cm–2 achieved at overpotentials ranging between 0.48 and 0.52 V highlight the suitability of the new Ni complexes in CVD processes for the fabrication of thin film electrocatalysts.

Chemical Vapor Deposition of Cobalt and Nickel Ferrite Thin Films: Investigation of Structure and Pseudocapacitive Properties

“…Additional benefits of this precursor class, compared to more conventional precursors are the high reactivity, easy handling and straight forward synthesis. [ 25–27 ] The thermal properties of the most promising compounds 1 , 2, and 3 , depicted in Scheme 1, can be found in Table 1 .…”

“…The individual MOCVD processes for the binary materials have been developed on the basis of their existing published analogs. [ 25–27 ] As known from the literature, the iron and nickel precursors (compounds 2 and 3 ) form the desired Fe(III) and Ni(II) oxides at a deposition pressure of 100 Pa, a deposition temperature of 600 °C, 50 sccm N 2 flow and 50 sccm O 2 flow, [ 26,27 ] however, the Co precursor 3 afforded the spinel‐type Co(II)/(III) oxide. [ 25 ] Hence the Co(II) precursor is partially oxidized to Co(III), which is not desired for the deposition of cobalt ferrite.…”

“…This behavior is similar to the CVD processes for binary material in literature, which exhibit decreased growth rates at temperatures below 500 °C to 450 °C. [ 25–27 ] This can most likely be attributed to diffusion limitation at temperatures higher than 400 °C, while at 400 °C surface reaction kinetics appear to be the rate‐determining step. The observation that in the presumably kinetically controlled regime the CFO growth rates are considerably lower than the NFO growth rates may be an effect of the lower oxygen partial pressure in the CFO process.…”

“…Bis(4‐(methoxyethylamino)pent‐3‐en‐2‐onato)cobalt(II) ([Co(meki) 2 ], 1 ), bis(4‐(isopropylamino)pent‐3‐en‐2‐onato)iron(II) ([Fe( i pki) 2 ], 2 ) and bis(4‐(ethoxyethylamino)pent‐3‐en‐2‐onato)nickel(II) ([Ni(eeki) 2 ], 3 ) were synthesized according to literature. [ 25–27 ] Thermogravimetric metric measurements were carried out on a Seiko TG/DTA 6200/SII at ambient pressure with an applied heating ramp of 5 K min −1 from 30 °C to 550 °C under a constant nitrogen flow of 300 mL min −1 . The sample load amounted to approximately 10 mg. For the derivation of 1 Torr vapor pressure temperatures and molar evaporation rates stepped isothermal measurements were conducted.…”

“…In this study, metal organic chemical vapor deposition (MOCVD) processes known for the binary oxides of Fe, Co, and Ni, with chemically similar ketoiminate precursors, namely [Co(meki) 2 ] ( 1 ), [Fe( i pki) 2 ] ( 2 ), and [Ni(eeki) 2 ] ( 3 ), [ 25–27 ] were combined to fabricate CoFe 2 O 4 and NiFe 2 O 4 films respectively, as depicted in Scheme . The precursors were evaluated via thermogravimetric (TG) analyses in order to determine their compatibility.…”