But new work out of the University of California, Los Angeles (UCLA) could help lower the barrier to entry for consumers, with a device that uses sunlight to produce both hydrogen and electricity.

The UCLA device is a hybrid unit that combines a supercapacitor with a hydrogen fuel cell, and runs the whole shebang on solar power. Along with the usual positive and negative electrodes, the device has a third electrode that can either store energy electrically or use it to split water into its constituent hydrogen and oxygen atoms – a process called water electrolysis.

To make the electrodes as efficient as possible, the team maximized the amount of surface area that comes into contact with water, right down to the nanoscale. That increases the amount of hydrogen the system can produce, as well as how much energy the supercapacitor can store.