This is an idea that seems interesting at first glance, but it's really not. What's important for lift isn't the absolute weight of the gas; it's the ratio of

This is an idea that seems interesting at first glance, but it's really not. What's important for lift isn't the absolute weight of the gas; it's the ratio of the weight of the lifting gas to the surrounding air. What that means is while hydrogen gives you about 1kg/m3 lift a perfect vacuum bottle only gives you about 1.3kg/m3. It probably wouldn't make sense even if we had the necessary exotic materials.