Cans + seawater + coffee = fuel

Hydrogen could power engines and fuel cells without generating climate-warming emissions, but carrying the volatile gas around is risky. Old soda cans and seawater could provide an answer.

Aluminum reacts with water to produce hydrogen, but not if it is exposed to air, which creates an oxide barrier on its surface. Douglas Hart, SM ’85, an MIT professor of mechanical engineering, and colleagues had previously shown they could keep the oxide at bay by pretreating the aluminum with gallium indium, but that’s fairly expensive. Now, they’ve shown that running the reaction in a solution of ions helps the alloy precipitate into a form that can be scooped out and reused to generate more hydrogen.

“Lucky for us, seawater is an ionic solution that is very cheap and available,” says Aly Kombargi, a PhD student and lead author of the team’s paper. “I literally went to Revere Beach with a friend and we grabbed our bottles and filled them, and then I just filtered out algae and sand.”

Unfortunately, the reaction happened much more slowly than it had in fresh water. But on a lark, Jonathan Slocum ’14, SM ’15, ScD ’18, tossed in some coffee grounds and was surprised to find that this sped things up. Kombargi ultimately determined that adding a component of caffeine made it possible to generate in five minutes the hydrogen otherwise produced in two hours.

The researchers are developing a small reactor that could run on a marine vessel or underwater vehicle to produce hydrogen on demand.