Energy is not really made by the brain but transformed from one state into another. All the cells (including neurons) in our bodies use sugar (glucose) for energy. In the case of neurons this glucose is converted into electrical energy that is passed between neurons. When we die the body stops converting sugar and no more energy is transformed in the brain.
I’m not certain, but I guess any remaining electrical energy will discharge away from the body. All the energy in our cells will eventually transform into different things as we decompose – not a pleasant thought I know.
Ooh, this is a really interesting question – it’s actually not something I’ve ever thought about before!
As your body has died, the energy creating reactions in your cells will no longer be occurring, so there will be no more energy being created. I assume that the energy currently in the cells will simply be used up as you die, and it’s the lack of energy that finally causes the body and brain to stop functioning and for you to die. But I’m not sure that is right, it may be that there’s a bit of energy left in your brain when you die, and somehow it passes out of your body.
But I’m afraid this is all me theorising, I don’t know. It’s a very interesting question though – do you have a theory about what may happen?