Hydride ions, which consist of 2 electrons and 1 proton, are promising negative charge carriers for next-generation electrochemical devices because of their low mass and high reduction/oxidation potential.
"As a negative charge carrier, the hydride ion (H) is more energetic, polarizable and reactive than cations [positively charged ions]," write the authors of a new study published in Nature this week.
"An H-mediated electrochemical process is fundamentally different from existing systems and enables the development of innovative electrochemical devices, such as rechargeable batteries, fuel cells, electrolysis cells and gas separation membranes.
"Using hydrogen as charge carriers can avoid the formation of detrimental metal dendrites, in principle, which creates new research avenues for clean energy storage and conversion."
However, the practical applications of this technology have been hindered by a lack of suitable electrolytes which can conduct hydride ions quickly, but not electrons, while displaying high thermal stability and compatibility with electrodes.
The authors have developed a new 'core-shell hydride ion electrolyte' which ticks all the boxes. The researchers used it to make the first prototype of a completely solid-state rechargeable hydride ion battery.
The electrolyte is composed of a thin shell of barium hydride (BaH) which encapsulates a core of cerium trihydride (CeH). The structure - 3CeH@BaH - allows hydride ions to be conducted quickly at room temperature.
The battery's positive electrode, or cathode, was made of sodium aluminium hydride (NaAlH), a classical hydrogen storage material. The negative electrode, or anode, was made of CeH.
"At the cathode side, electron flows in from the external circuit and H moves out to the electrolyte," the authors explained in the study.
"At the anode side, H injects into the ... lattice and electron moves out to the external circuit."
This generates an electric current.
"We further constructed a multi-layer stacked battery to increase the battery voltage to 1.9 V, which successfully lit a yellow LED light, demonstrating that a hydride ion battery can be used to power electrical devices," they write.