PEFCs are penalized by their cost and complexity, due in part to needed cooling and humidification systems. Evaporative cooling concepts achieve simultaneous cooling and humidification by evaporating liquid water in the PEFC itself, thus allowing the removal of the costly external humidifiers and the use of much less water for cooling than a classical convective cooling system. However they have their own challenges, such as distributing the liquid water where it is most needed or avoiding flooding the cell.