Atomic Layer Deposition of Ultrathin Nickel Sulfide Films and Preliminary Assessment of Their Performance as Hydrogen Evolution Catalysts

Abstract

Transition metal sulfides show great promise for applications ranging from catalysis to electrocatalysis to photovoltaics due to their high stability and conductivity. Nickel sulfide, particularly known for its ability to electrochemically reduce protons to hydrogen gas nearly as efficiently as expensive noble metals, can be challenging to produce with certain surface site compositions or morphologies, e.g., conformal thin films. To this end, we employed atomic layer deposition (ALD), a preeminent method to fabricate uniform and conformal films, to construct thin films of nickel sulfide (NiS x ) using bis­(N,N′-di-tert-butyl­acetamidinato)­nickel­(II) (Ni­(amd)2) vapor and hydrogen sulfide gas. Effects of experimental conditions such as pulse and purge times and temperature on the growth of NiS x were investigated. These revealed a wide temperature range, 125–225 °C, over which self-limiting NiS x growth can be observed. In situ quartz crystal microbalance (QCM) studies revealed conventional linear growth behavior for NiS x films, with a growth rate of 9.3 ng/cm2 per cycle being obtained. The ALD-synthesized films were characterized using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) methods. To assess the electrocatalyitic activity of NiS x for evolution of molecular hydrogen, films were grown on conductive-glass supports. Overpotentials at a current density of 10 mA/cm2 were recorded in both acidic and pH 7 phosphate buffer aqueous reaction media and found to be 440 and 576 mV, respectively, with very low NiS x loading. These results hint at the promise of ALD-grown NiS x materials as water-compatible electrocatalysts.

Structure‐Tailored Non‐Noble Metal‐based Ternary Chalcogenide Nanocrystals for Pt‐like Electrocatalytic Hydrogen Production

“…Tafel slope analyses on NBS_20, NBS_15, and NBS_12.5 nanoparticles provide Tafel slopes of 58, 83, and 95 mV dec −1 , respectively (Figure 3d), which propose that HER is based on Volmer–Heyrovsky mechanism for all the catalysts. The obtained value of Tafel slope is lower than most of the other non‐Pt‐based electrocatalysts such as Ni‐Pd 17 Se 15 (91.5 mV dec −1 ), [36] Ni 5 P 4 ‐Ni 2 P nanosheets (79.1 mV dec −1 ), [37] Cu 3 P (67 mV dec −1 ), [38] NiS x film (62 mV dec −1 ), [39] and NiCoS (61 mV dec −1 ) [40] . A lower charge‐transfer resistance was obtained with increase of irradiation time indicating better charge‐transfer kinetics and higher activity (Figure 3e).…”

Atomic‐Layer‐Deposition‐Based 2D Transition Metal Chalcogenides: Synthesis, Modulation, and Applications

“…[103] Similar results were reported for silicon and FTO substrates for application as HER catalysts. [104] The surface chemistry during the ALD of NiS x using Ni(amd) 2 and H 2 S was investigated in detail with versatile in situ analysis methods such as XPS, low-energy ion scattering spectroscopy, QCM, and QMS. [105] The formation of a nonvolatile acid-base complex of the acidic sulfhydryl and basic amidine on the surface during the H 2 S half cycle created an unconventional ALD scheme, which reduced the film growth rate.…”

Application of atomic layer deposition in fabricating high-efficiency electrocatalysts

“…The activity enhancement was attributed to the nanoporous structures formed in situ during the OER, which could offer an increased surface area to expose more catalytic active sites [95]. In addition to Ni9S8, Ni3S2, NiS2, and amorphous NiSx could also be synthesized through ALD by varying the precursors and the deposition temperature [96,97]. Generally, a relatively low deposition temperature favors the synthesis of amorphous nickel sulfides, while a relatively high deposition temperature favors the synthesis of crystalline nickel sulfide.…”