In a PEM fuel cell, there are catalyst particles dispersed in the catalyst layer (CL) to increase the electrochemically active area. You model this as jo=jo sigma, where sigma is the catalyst layer thickness. As you increase the CL thickness, the activation losses will therefore decrease, but the concentration losses will increase. Using this simple model, and considering only activation and concentration losses, find an expression for the optimum CL thickness to minimize voltage losses. Your answer should depend on current and other relevant factors.