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.
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