Carbon-Supported, Size-Tunable Ni Nanoparticles by Atomic Layer Deposition

Uniform Nickel Nanoparticles (Ni NPs) on carbon black were synthesized by fluidized-bed reactor atomic layer deposition (FBR-ALD). ALD behavior was first established on SiO2 using Ni(dmamb)2 and NH3, yielding pure Ni films with a saturated growth rate as precursor and reactant pulse times increased and exhibiting linear thickness depending on ALD cycle. Based on this, a Ni catalyst was synthesized and its NPs size was controlled by varying ALD cycles from 5 to 30. Thermogravimetric analysis (TGA) demonstrated that Ni loading on carbon increased linearly with the ALD cycle. Transmission electron microscopy (TEM) showed uniformly dispersed Ni NPs with size from 2.08 to 3.95 nm, and a decrease in areal density from about 2000 to about 1400 counts/µm2 as cycles increased, without severe agglomeration. X-ray photoelectron spectroscopy (XPS) indicated a size-dependent balance between metallic Ni and surface oxide. Small NPs were readily oxidized, and larger NPs displayed a stronger metallic binding state due to the lower surface-to-volume ratio. In 1 M KOH, hydrogen evolution reaction (HER) tests were conducted, indicating that the 20 cycle Ni/C catalyst showed the best performance, with an overpotential of 0.051 V at 10 mA/cm2 and a Tafel slope of 114 mV/dec. This ALD route enables uniform Ni NPs with tunable size and surface chemistry and can be extended to Ni based alloy catalyst NPs and atom level control of Ni to produce more efficient hydrogen catalysts.