Heat‐Treated Transition Metal‐N x C y Electrocatalysts for the O ₂ Reduction Reaction in Acid PEM Fuel Cells

Substitution of platinum or platinum group metals in low-temperature acidic fuel cells with catalysts based on cheaper and more abundant elements is much hoped for, not only for cost reason but also for the long-term sustainability of this technology. This chapter gives a comprehensive view on the current state of the knowledge in Metal/N/C catalysts for the oxygen reduction reaction in acidic PEM fuel cells, where the most promising metals are usually Fe or Co. While a short review of the historic milestones that have paved the way of this research field is introduced, a particular attention is given to the research results of the last decade. The main synthesis approaches investigated to date are described in detail, including their intrinsic (dis)advantages and state-of-the-art results. The multiparametric aspect of such catalysts is then reviewed in a section discussing the main parameters controlling the activity of such catalysts, namely the pyrolysis temperature, nature and content of the metal, nature and content of the nitrogen functionalities and morphology of the carbonaceous material host. Further zooming into the microscopic features of such catalysts, characterization of their active sites by advanced spectroscopic techniques is reviewed. Finally, aspects of the oxygen-reduction-reaction mechanism on such active sites are concluded with.