The pH of the solution would need to be low (acidic) to create a high H+ concentration on the outer portion of the membrane while there is a lower H+ concentration within the matrix of the mitochondria. This creates a concentration gradient that can lead to the production of ATP by ATP synthetase.
Work Step by Step
The mitochondrial cristae can pass electrons along the electron transport chain as well as move H+ into the intermembrane resulting in an electrochemical gradient. H+ moves down that gradient and the energy generated results in production of ATP.