High pressure synthesis and stability of cobalt hydrides - Mengnan Wang

APRIL 18, 2018

The synthesis and properties of hydrogen-bearing compounds is an intensively studied area of physics and chemistry, mainly driven by hydrogen-storage applications. High pressure and high temperature have been an effective route to synthesis hydrides with extremely high hydrogen content. A new study by RTH lab, reports the discovery of new cobalt compounds, CoH and CoH2, with high hydrogen content of 3.3 wt% and a volumetric hydrogen density of 214g/L. This study is published in J. Chem. Phys.

By compressing pure cobalt and hydrogen at 300K, the authors observed the formation of CoH and a new dihydride, CoH2, through x-ray diffraction. The formation of CoH is observed at pressures of 4 GPa and persists to 45 GPa. At this pressure, and with time, the authors observe the slow transformation of CoH to CoH2. This reaction can also be expedited at lower pressures (36 GPa) through laser heating.

As a first-row transition metal, cobalt has relatively lower mass than other transition metals, and as a result CoH2 has a high hydrogen density compared to analogous transition metal hydrides.

The first author of the study is Mengnan Wang, a Masters student of Dr. Ross Howie at HPSTAR. The work also involved Jack Binns, Mary-Ellen Donnelly and Philip Dalladay-Simpson of HPSTAR and was in collaboration with Dr Miriam Peña-Alvarez of the University of Edinburgh.

Caption: Crystal structures of cobalt hydride (CoH) and cobalt dihydride (CoH2). The cobalt atoms form an fcc lattice with hydrogen atom (white) occupying the octahedral sites in CoH. With increasing pressure hydrogen atoms occupy the tetrahedral sites, sharply increasing the unit-cell volume in CoH2.

金属氢化物一直是物理和化学研究领域的热门课题。北京高压科学研究中心RTH 课题组一直致力于氢以及氢化合物的研究。该团队利用原位高温高压X射线衍射等研究手段合成了Co的多氢化合物CoH和 CoH₂，并对新化合物的稳定性进行了研究。Co作为首周期过渡金属，相对原子质量远小于同族其余原子，这使得CoH2具有更高的氢含量（3.3wt%）和密度（214g/L）。本项研究为新型过渡金属多氢化合物的合成提供了新思路，也为储氢材料的开发和应用提供了新的可能。