Hydrogen makes metals brittle.

水素で金属はもろくなる---ジェイテクトが耐水素環境用軸受を開発、FCVの安全性向上に貢献 | レスポンス（Response.jp）

Background to the development of bearings for hydrogen circulation pumps: There was a need for bearings that were resistant to hydrogen and water vapor.
Features of JTEKT's developed product: Durability and corrosion resistance have been improved by more than 10 times using new materials and heat treatment.
Effects of JTEKT's developed product: In addition to increasing the safety and reliability of FCVs, it has become possible to use them in applications that are not limited by hydrogen embrittlement.