Here's a simplified version: energy generation in the mitochondria is based on the energy differential between the intermembrane space and the inner mitochondri

Here's a simplified version: energy generation in the mitochondria is based on the energy differential between the intermembrane space and the inner mitochondrial membrane (I may have confused those membranes). Most uncouplers act to reduce that differential, thus causing inefficiency in the system, which is lost as heat. tl;dr uncouplers mess with H+ ions.