How does electron transfer across a photosynthetic membrane store energy?

Electron transfer across the photosynthetic membrane stores energy by establishing a proton concentration gradient and an electrical charge across the thylakoid lamellae, a process central to the chemiosmotic theory.12

As electrons move through the electron-transport chain, protons are released into the inner thylakoid space through the oxidation of water and the movement of quinone molecules. Because the membrane is impermeable to these protons, they accumulate inside the thylakoid, creating a higher concentration relative to the outside. This gradient, combined with the separation of charge, creates potential energy analogous to a charged battery.134

This stored energy is subsequently used to drive the synthesis of ATP from ADP and inorganic phosphate. An enzyme complex, often called the ATP-ase complex, provides a channel for protons to flow back across the membrane, utilizing the energy of this flow to catalyze the formation of ATP.14