Rather than emit greenhouse gases into the atmosphere the way gasoline does, fuel cells running on hydrogen release water. Until now, the clean way to produce hydrogen required the use of prohibitively expensive precious metals. Now, researchers have developed a water-splitting device that runs on ordinary, store-bought batteries. The work was published in Nature Materials this week.
By combining stored hydrogen gas with oxygen from the air, hydrogen fuel cells produce electricity to power cars. But some so-called zero-emissions vehicles run on hydrogen made from natural gas, which is still a fossil fuel.
For a truly emissions-free way to produce hydrogen, scientists use electric currents to split the hydrogen and oxygen atoms in water -- a process called electrolysis. Stick two electrodes into pure water, pass electricity through them, and then hydrogen appears at the negatively-charged cathode while oxygen appears at the positively-charged anode, Science explains. The problem is, those electrodes require precious metal catalysts. The expensive metals conduct electricity well without decaying in water too easily.
For a cheaper water splitter, a team led by Hongjie Dai from Stanford turned to inexpensive, abundant nickel and iron for their electrocatalysts. These were enough to split water at room temperature with a single 1.5-volt battery (pictured above). Notice how the gases are bubbling up to the surface. (You can see it clearer in this video.)
“This is the first time anyone has used non-precious metal catalysts to split water at a voltage that low,” Dai explains in a news release. “It's quite remarkable, because normally you need expensive metals, like platinum or iridium, to achieve that voltage."
And as it turns out, a nickel/nickel-oxide structure was more active than pure nickel metal or pure nickel oxide alone. "This novel structure favors hydrogen electrocatalysis,” Dai says, “but we still don't fully understand the science behind it."
Because their inexpensive electrocatalyst lowers the voltage required to split water, the technology could save hydrogen producers billions in electricity costs if it makes it into large-scale production. But for the near future, the team is focusing on improving durability. Their electrodes decay slowly over time, and the current device runs for only days at a time. Their goal is to have it run for months.