Polymer electrolyte membrane fuel cells (PEMFCs) are one of the solutions for the transition towards an emission-free way of producing energy. PEMFCs in fact, are electrochemical devices which transform chemical energy into electrical energy without harmful emissions, if hydrogen is used as a fuel. However, the cathodic reaction, namely the oxygen reduction reaction (ORR), is sluggish. The best activities so far are yet assured by platinum-based electrocatalysts, which suffer of stability problems. Moreover, Pt is scarce and expensive, its price being linked to the stock exchange [1].
Non-noble transition metals such us Fe and Co, with nitrogen and carbon, in the shape of M-N-C, are the most promising alternative to Pt-based electrocatalysts. Transition metal is the heart of the electrocatalytic site for ORR, while nitrogen coordinates the transition metal atoms linking them to the carbon-based structure. Carbon has the purpose of conducting electrons and providing high specific surface area and porous structure [2]. The porous structure, in particular the microporous surface, is believed to provide a role in the formation of active sites for ORR [3], while the mesoporous structure plays a fundamental role in the working functioning on a PEMFC, favouring the transport of oxygen (reactant) and water (reaction product) [4]. In fact, the microporosity of the carbon material has a great impact on flooding of the cathodic catalytic layer, limiting the performance of the PEMFC. If water is not properly removed, its accumulation into the pores leads to a decreasing fuel cell performance due to pore clogging and subsequent oxygen deficiency.