[maxerickson]

They work by controlling a reversible chemical reaction. This control is done by keeping various things separated. To some approximation, they wear out because the stuff doesn't stay separated, it starts to mix, and starts to break down into other chemicals or whatever (and thus isn't available for the intended reversible reaction).

[lazide]

Some neat details , including some cool pictures.

[https://faraday.ac.uk/wp-content/uploads/2021/04/Faraday_Ins...]