Diffusion is a form of passive transport, which implies that it does not require the use of energy.
Diffusion is defined as the movement of particles from an area of higher concentration to an area of lower concentration. In other words, particles experiencing diffusion move “down their concentration gradient." This movement is the result of the random kinetic motion of the particles within a substance. Kinetic energy is the energy of motion. All particles are in constant, random motion. It is this motion that results in the diffusion of particles from an area of high to low concentration until a state of equilibrium has been reached.
On the other hand, energy is required in the form of ATP (adenosine triphosphate) when particles move from areas of low centration to areas of high concentration. This form of transport is known as active transport. When occurring in a cell, active transport utilizes a protein carrier that is embedded within the cell membrane.