Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are electrochemical devices useful for power generation and as sensors. PEMFC based power sources are candidates to replace internal combustion engines in automotive applications and batteries in portable electronics. The advantage of PEMFCs over internal combustion is higher energy conversion efficiency and thus fuel economy. In portable electronics, PEMFC power sources do not require replacement (primary batteries) nor recharging (secondary batteries) but will convert chemical energy to electric energy as long as suitable fuel (usually H₂) and oxidant (usually O₂ from air) are available. Despite these advantages, significant technological challenges must be overcome before PEMFC power sources become economically viable.

The most important limiting factor to widespread PEMFC use may be the fuel. While hydrogen fuel has been championed in the popular press as the energy carrier of the future, significant impediments remain that include cost and safety associated with the delivery and storage of a highly volatile, flammable gas. One potential solution is to convert hydrogen rich liquid fuels like gasoline and renewable fuels like ethanol and methanol into hydrogen gas by a process known as reformation. The resulting reformate, a gaseous mixture of H₂, CO₂, and CO, is delivered as needed to PEMFC power supplies provided PEMFCs employed are tolerant to CO.

Polymer coated magnetite (Fe₃O₄) microparticles have been shown to significantly increase (PEMFC) tolerance to CO when incorporated into PEMFC catalyst layer(s). The intrinsic magnetism of the particles and the nature of the particle polymer sheaths (e.g., hydrophilicity) are critical aspects that affect the CO tolerance displayed by resulting PEMFCs.

PEMFCs are often employed as sensors in portable instruments for detection and quantification of ethanol in human breath samples. Here, PEMFCs are used to sense ethanol, by-products from cigarette smoke, and acetone in human breath samples. Improved data analysis allows discrimination between cigarette smoke and ethanol in mixed samples. More robust field measurements are realized because ethanol is quantified in the presence of cigarette smoke. Acetone levels in breath have been shown to correlate with metabolic states in human subjects. PEMFC based portable acetone sensors could soon aid management of diabetes.