It also looks like these machines could harvest lithium, too.

One problem with renewably-produced hydrogen is that it uses fresh water – and with a quarter of the world's population already facing severe water scarcity at least one month of every year, freshwater is an ever more finite and precious resource. So technologies that can electrolyze hydrogen out of the abundant seawater that blankets most of the planet are a vital area of enquiry.

You can desalinate seawater and then split it, but it's not a great solution; most of your input energy is lost in the desal process, and that drives up the price of the hydrogen you're making. There are also plenty of direct seawater electrolysis machines, but most die too quickly to be useful in a commercial sense; choride ions in the complex ocean brew turn into highly corrosive chlorine gas at the anode, and it eats away the electrodes and degrades the catalysts until the machine stops working.

Researchers at China's Nanjing Tech University believe they've found a way around this problem. In a study published in Nature last month, the Nanjing team demonstrated a direct seawater electrolysis machine that ran for more than 3,200 hours (133 days) without failing. They say it's efficient, scalable and operates much like a freshwater splitter "without a notable increase in operation cost."

The team's electrolyzer keeps the seawater completely separate from the concentrated potassium hydroxide electrolyte and the electrodes using cheap, waterproof, breathable, anti-biofouling, PTFE-based membranes. These membranes stop liquid water from getting through, but they do let water vapor through. The difference in water vapor pressure between the seawater side and the electrolyte side "provides a driving force for spontaneous seawater gasification (evaporation) at the seawater side."