Hydrogen fuel cells present a low-emission means of powering vehicles. Proton-exchange membrane fuel cells (PEMFCs) are a relatively mature technology, already powering commercially available cars. An alternative to the PEMFC is the hydroxide-exchange membrane fuel cell (HEMFC), which is at an earlier stage of development and operates in an alkaline — rather than acidic — environment. The conditions in a HEMFC are less corrosive than in a PEMFC, allowing the use of non-precious metal electrocatalysts alongside cheaper materials for other components, including the bipolar plates and the ionomers found in the electrodes and membranes. While HEMFCs may present some savings, how they translate into overall system costs is still unclear. Now, Reza Abbasi, Brian Setzler and Yushan Yan at the University of Delaware analyse the cost of HEMFC systems for use in light-duty vehicles and identify developments needed for them to meet the US Department of Energy’s targets.
The researchers find that — despite the high cost of precious metals — it is better to use precious metal catalysts, rather than those free of them, at the electrodes. This is because state-of-the-art precious metal catalysts have superior intrinsic activity, enabling higher stack power density and therefore smaller stack areas, lowering costs. Moreover, while the team find that HEMFC stacks are cheaper than PEMFC stacks, the overall system is actually more expensive. This is largely down to the need for an additional device that scrubs CO2 from the air feed in HEMFCs and higher humidification management costs — both of which arise from the specific chemistry of the HEMFC environment.
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