This PhD thesis presents work on developing freestanding carbon electrodes for the oxygen reduction reaction application cost-effectively and sustainably. Within different alternatives to the high-cost Pt catalysts, heteroatoms and transitional metals modified carbon electrocatalysts have shown great promise to reduce the use of Pt. Meanwhile, synthesising freestanding catalysts has drawn interest due to the advantages of being binder-free, fewer manufacturing steps, and high recyclability. The first part of this thesis focuses on synthesising a freestanding carbon electrode with a hierarchical porosity and abundant nitrogen-doped sites. The carbon electrodes were synthesised through hydrothermal carbonization, followed by a pelleting process and further carbonization. Uniformly dispersed nitrogen sites and high specific surface area were obtained for the carbon electrodes. The electrochemical activity showed high stability in the freestanding configuration, and I found only the surface of electrode was reducing oxygen. The second part focuses on improving the carbon electrode's catalytic performance via post functionalization of the as-obtained nitrogen-doped carbon electrodes. Functionalization was carried out by immersing the carbon electrode into Fe solutions and followed by carbonization. The Fe was found to exist mainly as single sites. The electrochemical performance showed doubled current density compared to without Fe, and 100,000 s (27.77 h) stability was observed at 0.5 V. Through ex-situ X-ray absorption spectroscopy and electron paramagnetic resonance studies, Fe sites were found responsible for reducing oxygen. The third part focuses on the scalable synthesis of a low-cost iron, nitrogen co-doped carbon. Powdered iron, nitrogen co-doped carbon catalysts was prepared by hydrothermal carbonization and high-temperature post carbonization. FeN4 was found to be the main iron existing form in the obtained catalysts. Two different precursors containing Fe2+ and Fe3+ are compared. Both chemical and structural differences have been observed in catalysts starting from Fe2+ and Fe3+ precursors. Furthermore, this catalyst is studied in an anion exchange membrane fuel cell.