Q:

What is an electron reservoir?

I always meet the word "reservoir", such as electron reservoir.
I was wondering what exactly the reservoir is. Is it means a metal that provides electrons?

A:

Electron reservoirs as you say can store electrons, but they can accept and release electrons in a reversible fashion too.

Electron reservoirs and molecular wires are basic motifs of single-electron devices. Both can accept and release electrons in a reversible fashion, but the former can also store electrons. 

https://pubs.acs.org/doi/pdf/10.1021/om060364l

