Synthesis of Ni-Ru alloy nanoparticles and their high catalytic activity in dehydrogenation of ammonia borane

We report the synthesis and characterization of new NixRu1−x (x=0.56–0.74) alloy nanoparticles (NPs) and their catalytic activity for hydrogen release in the ammonia borane hydrolysis process. The alloy NPs were obtained by wet-chemistry method using a rapid lithium triethylborohydride reduction of Ni2+ and Ru3+ precursors in oleylamine. The nature of each alloy sample was fully characterized by TEM, XRD, energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We found that the as-prepared Ni–Ru alloy NPs exhibited exceptional catalytic activity for the ammonia borane hydrolysis reaction for hydrogen release. All Ni–Ru alloy NPs, and in particular the Ni0.74Ru0.26 sample, outperform the activity of similar size monometallic Ni and Ru NPs, and even of Ni@Ru core-shell NPs. The hydrolysis activation energy for the Ni0.74Ru0.26 alloy catalyst was measured to be approximately 37 kJ mol−1. This value is considerably lower than the values measured for monometallic Ni (≈70 kJ mol−1) and Ru NPs (≈49 kJ mol−1), and for Ni@Ru (≈44 kJ mol−1), and is also lower than the values of most noble-metal-containing bimetallic NPs reported in the literature. Thus, a remarkable improvement of catalytic activity of Ru in the dehydrogenation of ammonia borane was obtained by alloying Ru with a Ni, which is a relatively cheap metal.