Based off of the concept of motional emf, it seems as if metallic objects revolving around the earth must develop a potential difference across them.
Wouldn't it be possible to exploit this potential difference? It seems as if it would be an infinite energy source? How is energy conserved here?
It is possible to exploit this. It has been done. See the Physics LibreTexts chapter on Motional Emf.
Just producing a potential difference in a moving conductor does not produce energy. It is a like the fact that a battery has a potential difference across its terminals does not mean the battery is producing energy. The energy comes if the circuit is completed and a current flows.
Think about the force on a conductor moving in a magnetic field. Think about the work from that force. That should tell you how energy is conserved and where it comes from.
