Decoupling of Light\nand Dark Reactions in a 2D Niobium\nTungstate for Light-Induced Charge Storage and On-Demand Hydrogen\nEvolution

The direct coupling of light harvesting and charge storage\nin a\nsingle material opens new avenues to light storing devices. Here we\ndemonstrate the decoupling of light and dark reactions in the two-dimensional\nlayered niobium tungstate (TBA)<sup>+</sup>(NbWO<sub>6</sub>)<sup>−</sup> for on-demand hydrogen evolution and solar battery\nenergy storage. Light illumination drives Li<sup>+</sup>/H<sup>+</sup> photointercalation into the (TBA)<sup>+</sup>(NbWO<sub>6</sub>)<sup>−</sup> photoanode, leading to small polaron formation assisted\nby structural distortions on the WO<sub><i>x</i></sub> sublattice,\nalong with a light-induced decrease in material resistance over 2\norders of magnitude compared to the dark. The photogenerated electrons\ncan be extracted on demand to produce solar hydrogen upon the addition\nof a Pt catalyst. Alternatively, they can be stored for over 20 h\nunder oxygen-free conditions after 365 nm UV illumination for only\n10 min, thus featuring a solar battery anode with promising capacity\nand long-term stability. The optoionic effects described herein offer\nnew insights to overcome the intermittency of solar irradiation, while\ninspiring applications at the interface of solar energy conversion\nand energy storage, including solar batteries, “dark”\nphotocatalysis, solar battolyzers, and photomemory devices.