Rechargeable Zn-H 2 O hydrolysis battery for hydrogen storage and production.

Reactive metals hydrolysis offers significant advantages for hydrogen storage and production. However, the regeneration of common reactive metals (e.g., Mg, Al, etc.) is energy-intensive and produces unwanted byproducts such as CO 2 and Cl 2 . Herein, we employ Zn as a reactive mediator that can be easily regenerated by electrolysis of ZnO in an alkaline solution with a Faradaic efficiency of >99.9 %. H 2 is produced in the same electrolyte by constructing a Zn-H 2 O hydrolysis battery consisting of a Zn anode and a Raney-Ni cathode to unlock the Zn-H 2 O reaction. The entire two-step water splitting reaction with a net energy efficiency of 70.4 % at 80 °C and 50 mA cm -2 . Additionally, the Zn-H 2 O system can be charged using renewable energy to produce H 2 on demand and runs for 600 cycles only sacrificing 3.76 % energy efficiency. DFT calculations reveal that the desorption of H* on Raney-Ni (-0.30 eV) is closer to zero compared with that on Zn (-0.87 eV), indicating a faster desorption of H* at low overpotential. Further, a 24 Ah electrolyzer is demonstrated to produce H 2 with a net energy efficiency of 65.5 %, which holds promise for its real application.