## 1 Introduction  
Bioelectrochemical Systems (BESs) are classified as one of the most attractive renewable technology for energy conversion [1, 2]. Among the various BESs, Microbial Fuel Cells (MFCs) allow simultaneous electrical energy harvesting and wastewater treatment [1, 3, 4, 5, 6, 7] by the catalytic action of microorganisms, which oxidize the organic matter in the waste at the anode side of the cell to produce carbon dioxide, protons and electrons. Protons and electrons migrate through an external circuit and recombine with oxygen at the cathode side, producing water [1, 4]. However, MFC technology is still in a pioneer stag, due to various critical issues to overcome. One of these issues is the slow kinetics of oxygen reduction reaction (ORR) at the cathode side and the need for a highly efficient catalyst for a fast reduction of oxygen to water involving a four-electron pathway [4, 8, 9, 10, 11]. Hence, the development of effective and low-cost electrocatalysts is of crucial importance to develop highly efficient and durable MFC systems. In this context, many studies have been addressed to develop alternative catalysts to noble metals (i.e., platinum), which are expensive, rare and sensitive to poisoning [3, 8]. Platinum-group-metal-free (PGM-free) catalysts represent a very promising category of new catalysts due to their tuneable composition based on transition metals (Fe, Ni, Co, Mn, Cu) supported on carbon substrates (graphene, graphene oxide, carbon nanotubes, black pearls, carbon black and biochar), which are also doped with heteroatoms (N, P, S, O) [12, 13, 14, 15, 16, 17, 18, 19, 20]Among PGM-free catalysts, metal-nitrogen-carbon (M-N-C) materials have been widely investigated toward ORR in acidic and alkaline pH, whereas the study of ORR in neutral media still accounts for few reports [6, 8, 12, 21, 22]. So far, attention has been paid to the development of Fe-N-C catalysts, and the efficiency of active sites in Fe-N-C composites has been ascribed to the coordination of iron to nitrogen heteroatoms in FeNx structure, which cause a beneficial effect on the direct conversion of oxygen to water via a four-electron mechanism [1, 8, 10, 18]. In this context, the activation of carbon substrates via N-doping is crucial for stabilizing the coordination of transition metal, besides helping to maintain a high density of FeNx active sites for ORR and avoid the aggregation phenomena of the catalyst [3, 23, 24]. Among the various iron sources for FeN-C catalysts, Iron (II) phthalocyanine (FePc) has attracted a great interest due to its low-cost, tuneable electronic property, facile methods of synthesis, and low overpotential for oxygen reduction [1, 3, 4, 6, 9, 12, 25, 26, 27, 28, 29, 30, 31]. [PERSON] and coworkers have shown that the poor electron conductivity and stability of phthalocyanine complexes increase when FeN\({}_{4}\) macrocycles are incorporated on nitrogen-functionalized carbon supports and further submitted to pyrolysis treatment [32]. [PERSON] et al. verified that carbon-supported FePc greatly enhances ORR activity, owing to the interaction of the macrocycle with the support, which modulates electronic properties through a delocalized \(\pi\)-electron cloud [33]. By tuning the surface chemistry and morphology of the carbon support, metal stabilization through \(\pi\)-\(\pi\) interaction result in a good catalytic activity and durability in neutral media [34, 35, 36]. Surface area and porosity are also of paramount importance to increase catalytic activity towards ORR [37]. Two-dimensional (2D) FeN\({}_{4}\) catalysts with high surface area and porous structure have indeed demonstrated good performance in terms of oxygen reduction activity and long-term stability due to a synergistic effect of the high density of active sites and porosity, which favours high-mass transfer [24]. In addition, thermal treatments are crucial for Fe-N coordination and catalytic stability [38].