Does Air China have cell phone charge bays on the plane in economy class?

Carolyn, according to what I know, business and first class seats usually have sockets. You can use them to charge your phone. However, the pins might be different. Passengers should bring their adaptors. But I am afraid that there is no socket for economy class seats. And it usually depends on the plane model. I think you'd better confirm this with your airline.

Yes, you can bring power bank on the plane as it is required. However, you are not allowed to use it to charge your phone, according to aviation regulation.

It is actually not a problem. There are charging stations inside the airport. You can charge your phone before boarding the airplane.