Reversible Hydride Ion-Mediated Electrochemistry in Sodium Aluminum Hydride
Ren Zou1,2, Jirong Cui2, Qiyao Zou2
1Department of Chemical Physics, University of Science and Technology of China (USTC), Hefei 230026, P. R. China.
Abstract:
Electrochemical devices using hydride ions (H-) as charge carriers offer significant potential for hydrogen-based energy storage and conversion. However, only very few H- based electrochemical devices have been demonstrated, lacking details regarding the hydride ion-mediated reaction processes. In this work, we find that the NaAlH4 electrode can utilize at least 5.6 wt % H via an H--mediated reaction under ambient conditions. Further, the differences between H--mediated electrochemical reactions and traditional thermochemical processes are discussed from the perspectives of driving force, mass migration, and reaction kinetics. The thermally driven process is controlled by the enthalpy-entropy balance and the long-range mass transport. In contrast, the electrochemical pathway is driven by an electrochemical potential gradient and dominated by fast H- migration. Analyses of the interface and phase spatial distribution show that the electrode/electrolyte interfaces exhibit good compatibility at mild reaction conditions and suppression of detrimental phase separation. These findings highlight the unique advantages of H--mediated electrochemistry and provide a foundation for developing next-generation hydride-based energy storage and conversion technologies.
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