The electrochemistry of platinum is studied in the protic ionic liquids dimethylethylammonium trifluoromethanesulfonate, diethylmethylammonium trifluoromethanesulfonate and diethylmethylammonium bis(trifluoromethanesulfonyl)imide. Oxide layers form on platinum due to trace water oxidation in the ionic liquids at potentials of about 1.0 V and the oxide growth kinetics change as the potential increases Above 60 °C, multilayers of oxide form in each ionic liquid at high potentials. The hydrazine oxidation reaction was used as a probe of the reactivity of the oxide layers and significant differences in the behaviour of the [TfO]−-based ionic liquids and [dema][Tf2N] are observed during hydrazine oxidation. Specifically, significant “activation” of the Pt electrode towards hydrazine oxidation is observed in the [TfO]−-based liquids whereas the electrode appears to be poisoned rapidly in [dema][Tf2N]. The electrochemically formed oxide layers are sensitive to the presence of hydrazine dissolved in dimethylethylammonium trifluoromethanesulfonate and immersion of the “activated” oxide-coated Pt in a hydrazine/ionic liquid solution for extended periods of time results in deactivation of the platinum surface.