Scheduling hydrogen release from water: Photosynthesis splits water to provide protons and electrons for plant growth; oxygen is a by-product. When chemists split water, they're also more interested in making fuel, and the simplest product is hydrogen (a combination of protons and electrons). One challenge is keeping the reactive hydrogen and oxygen product streams separate. Rausch et al. present a scheme that captures the protons and electrons in a molecular cluster of silico-tungstic acid. Later, they expose the cluster to platinum, coaxing the acid into releasing hydrogen. Eliminating the mixing risk increases the potential for household use. Science , this issue p. 1326

Electrolytic water splitting to generate hydrogen and oxygen is one of the most promising ways in which to harness intermittent renewable power sources and store the energy these provide as a clean‐burning and sustainable fuel. In recent years, this has led to an explosion in reports on electrochemical water splitting, most of them focused on improving the efficiency of the electrochemical reactions themselves. However, efficient generation of hydrogen and oxygen is of little use if these products cannot be kept separate and the community is now coming to realize that there are considerable challenges associated with maintaining adequate separation between H₂ and O₂ during electrolysis driven by intermittent renewable sources. Decoupled electrolysis (whereby oxygen production occurs with reduction of a suitable mediator and hydrogen production is then paired with the reoxidation of this mediator) offers a solution to many of these challenges by allowing O₂ and H₂ to be produced at different times, at different rates, and even in completely different electrochemical cells. In this review, an overview of recent progress in the field of decoupled electrolysis for water splitting is given and the potential that this approach has for enabling a range of other sustainable chemical processes is explored.