By adding cobalt and phosphates to water and passing a mild current through the solution with a glass electrode, Matthew Kanan and Daniel Nocera of the Massachusetts Institute of Technology (MIT) were able to break water apart and force oxygen to bubble to the surface.

ECONOMIST: Looking to leaves for a way to store solar power after sunset

This reduced current is detected by the sensor via the gold electrode.

ECONOMIST: Medical diagnostics

The resin within the carbon layers is laced with lithium ions, so that each layer acts like an electrode, causing the positively charged lithium ions to collect in one layer when a voltage is applied, and a current to flow when the sandwich is placed in a circuit.

ECONOMIST: Carbon-composite batteries