"Turner's design held the record for the highest solar-to-hydrogen conversion efficiency until 2015. But the acidic solution to which the cell was exposed while in use quickly broke it down, making the hydrogen it produced too expensive.
For the new design, researchers led by chemist Jing Gu of San Diego State University added coatings to the semiconductor layers to prevent acid corrosion. These protective coatings significantly extended the life of Turner's high-efficiency design and produced a PEC device that retains 80 percent of its capabilities in durability tests."
It doesn't say how long the life was extended with the added coatings. And it doesn't say what the efficiency is, just that 80% of its capabilities remain.