Surface area enhancement of nickel foam by low-temperature chemical alloying/dealloying and its application for sodium borohydride hydrolysis

Structured nickel catalysts for sodium borohydride hydrolysis (SBH) were synthesized by surface modification of nickel foam. The fabrication process consisted of i) nickel aluminization, ii) post-annealing, and iii) selective aluminum leaching. Through low-temperature chemical alloying, nickel was aluminized at 400 °C, and a 0.5 μm-thick NiAl₃ alloy outer-layer was formed. While discontinuing the influx of the aluminum source, post-annealing was conducted to transform the NiAl₃ outer-layer into different Ni–Al alloys, such as NiAl₃ on Ni₂Al₃, Ni₂Al₃ on NiAl, and NiAl on Ni₃Al at 400, 500, and 600 °C, respectively. After the selective aluminum leaching, the surface treatment increased the surface area by factors of 2.2–77.1, leading to a significant enhancement of activity in SBH hydrolysis. Additionally, the catalyst undergoing post-annealing at 400 °C achieved superior performance in both initial activity and durability, due to the adhesion layer of Ni₂Al₃ formed between the outermost catalytic layer and the nickel substrate. Finally, continuous SBH-based hydrogen generation using the catalyst with post-annealing at 400 °C was achieved and the as-developed nickel catalyst produced hydrogen at a rate of up to 400 ± 27 sccm/g_catalyst while exhibiting excellent durability for 3 h.