Hydrolytic H2 production behavior and mechanism of surface activated AZ91D alloy waste by borohydrides in neutral solution at room temperature

In this study, AZ91D alloy waste is initially activated using borohydrides (LiBH4, NaBH4, and KBH4), with a focus on examining the hydrolysis hydrogen production behavior and underlying mechanism. The results demonstrate that the hydrolysis rate of AZ91D alloy waste can be significantly augmented by various borohydride treatments, and particularly, the kinetic performance and hydrogen production capacity are concurrently improved when treated with KBH4 under neutral conditions at room temperature (298 K). The peak hydrogen production rate from AZ91D alloy waste activated by KBH4 reaches an impressive 223.6 mL·g−1·min−1 at merely 0.83 min, surpassing that of untreated AZ91D alloy waste, which records 40.4 mL·g−1·min−1 at approximately 11 min. Within 5 and 30 min, AZ91D-KBH4 treatment yields as much as 524.5 and 647.8 mL·g−1 H2, corresponding to a respective increase to 141.3 and 626.5 mL·g−1 H2 for the unactivated AZ91D alloy waste. Notably, AZ91D alloy waste activated with KBH4 exhibits efficient hydrogen production capability at room temperature, with its yield escalating from 0.25 to 0.51 within just 5 min. The calculated activation energy for AZ91D-KBH4 system is found to be 22.2 kJ·mol−1, notably lower than the value of 87.8 kJ·mol−1 for the unmodified AZ91D alloy waste. This superior enhancement in hydrolysis kinetics and hydrogen production capacity at room temperature is attributed to the preferential action of KBH4, which facilitates triggered mass transfer channels and synergistically regulates the nucleation and growth process of Mg(OH)2. The findings confirm that surface activation through borohydrides, especially KBH4, represents an efficacious strategy for transforming AZ91D waste alloy into a material capable of achieving high hydrolysis kinetics and producing greener hydrogen at ambient temperatures.