Catalytic Activities of Various Niobium Oxides for Hydrogen Absorption/Desorption Reactions of Magnesium

Keita Shinzato; Hiroyuki Gi; Toru Murayama; Masahiro Sadakane; Yongming Wang; Shigehito Isobe; Takayuki Ichikawa; Hiroki Miyaoka

doi:10.1021/acsomega.1c03687

Catalytic Activities of Various Niobium Oxides for Hydrogen Absorption/Desorption Reactions of Magnesium

ACS Omega. 2021 Sep 3;6(36):23564-23569. doi: 10.1021/acsomega.1c03687. eCollection 2021 Sep 14.

Authors

Keita Shinzato¹, Hiroyuki Gi², Toru Murayama^{3

4}, Masahiro Sadakane², Yongming Wang⁵, Shigehito Isobe⁶, Takayuki Ichikawa^{1

2}, Hiroki Miyaoka^{1

2}

Affiliations

¹ Natural Science Center for Basic Research and Development, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530, Japan.
² Graduate School of Advanced Science and Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan.
³ Research Center for Hydrogen Energy-based Society, Tokyo Metropolitan University, Tokyo 192-0397, Japan.
⁴ Yantai Key Laboratory of Gold Catalysis and Engineering, Shandong Applied Research Center of Gold Nanotechnology (Au-SDARC), School of Chemistry & Chemical Engineering, Yantai University, Yantai 264005, China.
⁵ Creative Research Institution, Hokkaido University, N-21, W-10, Sapporo 001-0021, Japan.
⁶ Graduate School of Engineering, Hokkaido University, N-13, W-8, Sapporo 060-8628, Japan.

Abstract

Five types of niobium(V) oxides (Nb₂O₅) were synthesized by hydrothermal and heat treatment processes, and their structural properties and catalytic activities for the hydrogen absorption/desorption reactions of magnesium were characterized. The synthesized Nb oxides were dispersed on magnesium hydride (MgH₂), a typical hydrogen storage material, using the ball-milling method. All the synthesized Nb oxides improved the reaction kinetics of the hydrogen desorption/absorption reactions. The catalytic activities for the hydrogen desorption were comparable, while the hydrogen absorption rates were significantly different for each synthesized Nb oxide. This difference can be explained by the structural stability of Nb₂O₅, which is related to the formation of a catalytically active state by the reduction of Nb₂O₅ during the ball-milling process. Notably, the highest catalytic effect was observed for Nb₂O₅ with a highly crystalline pyrochlore structure and a low specific surface area, suggesting that pyrochlore Nb₂O₅ is a metastable phase. However, only the amorphous Nb oxide was out of order, even though there is a report on the high catalytic activity of amorphous Nb oxide. This is attributed to the initial condensed state of amorphous Nb oxide, because particle size affects the dispersion state on the MgH₂ surface, which is also important for obtaining high catalytic activity. Thus, it is concluded that Nb₂O₅ with lower stability of the crystal structure and smaller particle size shows better catalysis for both hydrogen desorption and absorption reactions.