**5. Conclusions**

A set of Al-Ga-In3Sn-Zn alloys was prepared. Through experiments and discussions, the hypothesis that Zn will change the hydrogen production performance of the alloy by entering the GB phase was verified, and it was found that the reaction mechanism cannot only be explained by the eutectic reaction of the GB phase and Al. We can draw the following conclusions:

(1) Zn-doped alloys mainly contain Al (Ga) solid solution, the intermetallic compound In3Sn, with a high probability of Al (Zn) solid solution. In addition, particles with high Zn content will appear in high-Zn alloys.

(2) In addition to grain size and segregation, the composition of the hydrogen-producing alloy also a ffects the change in activation energy.

(3) As Zn doping amount increases, the maximum hydrogen production rate always increases first and then decreases. At the same temperature, the reaction time of alloys with high Zn content is longer. At a moderate temperature, Al-Ga-In3Sn-(3 wt.%)-Zn not only has good hydrogen production performance, but also has high activation energy, which is conducive to its long-term storage and transportation.

(4) The present work indicates that the alloy hydrolysis reaction is promoted by the GB phase and the Al–Zn micro-galvanic cells.

**Author Contributions:** Writing—original draft, D.L.; writing—review and editing, Q.G.; formal analysis, D.L.; conceptualization, Q.G.; data curation, Q.A., H.W. and D.L.; investigation, D.L.; resources, J.W.; project administration, C.W. and Q.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** Financial support for this work was provided by the Industrial Innovation Special Fund Project of Jilin Province (2017C052-1, 2017C045-1).

**Acknowledgments:** Authors are grateful to editor and referees.

**Conflicts of Interest:** The authors declare no conflict of interest.
