system
Given the following post, respond as if you're commenting on Reddit:
human
When light strikes a metal, a photon can excite an electron to leave. Does the metal ever run out of electrons?
gpt
No. While releasing more and more electrons, the Fermi level will become lower and lower, because the electrons with largest kientic energy will be ejected. This increases the work function of the metal until the energy of one photon is not sufficient to excite another electron to the vacuum level. At this point you have changed the potential of the metal significantly. So you could call the photoelectric effect self-inhibiting if the metal is not connect to an electron source.



edit: additions due to many questions going in very similar directions:

*Q: Does a solar cell become less efficient due to depletion of electrons?*

A: No. First, a solar cell usually doesn't operate using the photoelectric effect but using an interface between two different doped semiconductors (p-n junction). But that difference is not really relevant. The thing is that after leaving the photoelectric electrode (or the electron donor phase in the semiconductor) they travel towards an electron acceptor electrode. This creates a potential between these electrodes. If both electrodes are floating (i.e. not connected to any mass or ground which can neutralize potential, this potential will then counteract any further charge separation. However, in a solar cell powered circuit, the to electrodes are connected to each other by a load (for example a lamp). The electrons travel through that load, lose their potential energy and travel back to the donor electrode where they replenish the electron reservoir and more electrons can be excited. This is a continuous process and electrons are not "lost" somewhere in between.

*Q: How does solar cells work in a spacecraft when there is no connection to ground?*

A: A circuit as described above can also contain the ground as electrical conductor. This does not change the efficiency of a circuit or lead to changes in potential. The only importance is that the two opposite poles of the load and the two opposite electrodes of the photoelectric element or solar cell are connect to the same potential each. You can do that directly, or can put the ground in between ONE leg. Not both, because then you would short the solar cell and not be able to power the load.

*Q: Does the metal become oxidized when electrons are released or does it degrade chemically?*

A: No. Even though the loss of electrons is formally an oxidation, the metal does not become oxidized because it will regain the electrons on one way or the other before that many electrons are lost so that a chemical process would set in. The removed electrons do not belong to a specific atom within the metal, but are rather shared between all atoms in an electron "sea" where they can freely move (hence the electric conductivity of metals).

But you can make chemical reactions more or less likely by applying a potential (voltage) to the metal. This is what is used in electrolysis or active passivation of metals. In principle you can tune the reactivity by lowering or increasing the energy of the most energetic electrons in the electron "sea", making it harder or easier, respectively, for oxidizing agents (e.g. O2, H^+ ) to remove electrons from the metal.