I bought 1 quart of live shrimp and put it in the bucket with the air pump. About 40% of the shrimp was dead after 3hours. whats the best way to keep them alive all night?

Here's the bucket i was using. Its the cool bubbles syrofoam bucket:

When it's a 100 degrees outside and you leave your bucket out in the sun all day, they're going to die. In the summer, I'll put them in one of these buckets and just tie a rope to them and leave them in the water, and I've kept shrimp alive in the middle of summer for 2 days before.
Or if you don't want to buy another bucket, then I'd get a small 12-20oz water bottle and freeze it overnight. The morning when you go fishing wrap that bottle up in a whole bunch of papertowels and put it in your icechest (this prevents it from melting too fast). By around 10am, its already too hot for the shrimp. Put that whole frozen bottle of water inside your bait tank. It'll cool down the water and help.

I've used these (or similar) before and kept shrimp alive for upwards of 3+ days, even on a single set of batteries running constantly. Keep them in the shade/cool. I would dump a handful of ice in there every couple of hours also. To be fair, they were in air conditioning after we went in for the night until the next afternoon/evening when we went back out. Personally I like to cull the dead ones asap. I don't know if it helps keep the oxygen level up, but it seems, like with minnows that more start dying when there are more dead ones in there. YMMV

One more thing, those buckets look awful short, I wouldn't try to put a whole pint in there. I actually got the lid & bubbler, and use it with a 5 gallon instead.

+1 on ice bottle too, you can never have enough frozen 20 oz bottles.

the bucket you have in the pic twin is only best for a pint of shrimp, quart is too much for that bucket. the frozen water bottle trick works except i put the bottle in zip lock bag. i would also get few fresh seaweed and put them in the bucket so the shrimp have somewhere to grab on.

Thanks for the tip guys. I mostly fish at night. So weather is int he 80s. I will put the shrimp in a 5 gallon bucket and add a handful of ice in there.

yea the 5 gallon bucket will help but dont just put in a handful of ice in there one time, only put a few pieces in at a time and do it every few hrs.