Borohydride (BH4 –) is rapidly attracting attention as an alternative fuel molecule for fuel cells due to its high gravimetric and volumetric energy densities, high power density, and avoidance of the carbon monoxide (CO) poisoning seen in hydrogen (H2) and methanol (MeOH) fuel cells. Here we describe an as-yet unreported poisoning process that occurs during BH4 – oxidation at Pt and Au anodes at low potentials (high fuel cell voltages). Though such poisoning can compromise the long-term performance of BH4 – fuel cells, we also demonstrate an in situ cleaning procedure for a BH4 – fuel cell using a Pt anode.