[Note: Thread moved to homework forum by mentor] This is one of my homework problems: You are designing a counter flow heat exchanger for cooling a KOH electrolyte pH (11) in an electrolysis unit. The liquid is saturated with hydrogen. One of your team members suggests using copper pipes for good heat transfer. Is this a good idea; explain? Hint the dashed lines represent the hydrogen and oxygen evolution potentials for water as a function of pH. The Pourbaix diagram is here. My Answer: For a solution saturated with hydrogen and in the alkaline region of the Pourbaix diagram, copper is a solid in a region of stability. Therefore, copper pipe is a good idea as there will be no oxidation of the copper pipe to CuO2 and copper ions will not be entering the KOH solution. I don't know if thsi answer is correct though. Some of my classmates said they thought it would corrode to Cu2O, but I thought we were supposed to use the bottom dashed line because it's in equilibrium with hydrogen. Thoughts please?