I just found this article that partially answer to your question.

https://phys.org/news/2013-01-nanosilicon-rapidly-electricity.html

In pure water, 10 nm nanosilicon generates 14 % of its own mass in hydrogen. So about 140 g of hydrogen per kg of nanosilicon. 

For 100 nm silicon, it's about 70 g per kg of nanosilicon.

And for bulk silicon, it's about 50 g per kg. 

The other advantage of 10 nm nanosilicon is that it generates hydrogen 1000 times faster than bulk silicon.

"This technology would require a large-scale, energy-efficient method of silicon nanoparticle production, but could have some advantages compared to other hydrogen generation techniques. "The key advantage of silicon oxidation for hydrogen generation is its simplicity," Swihart said. "With this approach, hydrogen is produced rapidly, at room temperature, and without the need for any external energy source. The energy needed for hydrogen generation is effectively stored in the silicon. All of the energy input required for producing the silicon can be provided at a central location, and the silicon can then be used in portable applications."

I think HPQ can answer to the large scale energy efficient method of silicon nanoparticle production.