PVG Shanghai Pu Dong to SHA Shanghai Hongqiao - 13 Hours Between - American Citizen

I am flying from the US to Hong Kong. My layover requires me to change airports in Shanghai. I have a little over 13 hours between flights. Is a visa needed for this? Do I need to apply once I get to the airport? What is the fee? I simply want to change airports...no visitng in the city.

Thank you!