Do I need a visa?

Hello,

My spouse and I both hold UK passports.

We are flying from London to Shanghai Pudong. We want to stay in China for 1.5 days before connecting onto Tokyo.

On my return from Japan to London, we will also fly through Shanghai but only for a few hours.

For my 1.5 day intended visit in Shanghai, firstly can I apply for the 72 transit visa? And also, how do I apply? Is it sufficient for me to just go to the airport on the day of the flight, inform the airline and then complete the dept/arrival cards as mentioned?