Materials basics for fuel cells

Humidification, steam delivery

Humidification of the hydrogen fuel is essential in low temperature PEMFC systems. This adds complexity and costs to the system, and significant efforts are in progress to minimise the need for humidification. Membrane humidification systems are commonly used in fuel humidification. Water purity is critical and is cleaned using deionising filters. Water is recovered from the exit gas to avoid the need for an external water circuit. High temperature PEM systems and PAFC systems have no humidification requirements.

Steam addition to the fuel stream is necessary for the reforming process of hydrocarbon fuels to hydrogen and for prevention of carbon deposition. The steam generator becomes a critical component in the BOP of hydrocarbon fuelled (natural gas, LPG, diesel, alcohol), and high temperature fuel cells. Water purity and constant flow steam generation (no pulsing) are challenging issues. Water can be supplied from external sources (water cleaning system needs to cope with the widely varying water quality at installation sites – identified as a common failure mode) or by condensing the fuel cell exhaust stream. However, even in the latter case a deionising filter may be essential to prevent depositions and clogging in the steam generator. For lowering the load on the steam generator part of the steam could be supplied by direct anode exhaust gas recycle [60].