Platinum group metal-free (PGM-free) ORR catalysts from the Fe-N-C family were synthesized using sacrificial support method (SSM) technique. Six experimental steps were used during the synthesis: 1) mixing the precursor, the metal salt, and the silica template; 2) first pyrolysis in hydrogen rich atmosphere; 3) ball milling; 4) etching the silica template using harsh acids environment; 5) the second pyrolysis in ammonia rich atmosphere; 6) final ball milling. Three independent batches were fabricated following the same procedure. The effect of each synthetic parameters on the surface chemistry and the electrocatalytic performance in neutral media was studied. Rotating ring disk electrode (RRDE) experiment showed an increase in half wave potential and limiting current after the pyrolysis steps. The additional improvement was observed after etching and performing the second pyrolysis. A similar trend was seen in microbial fuel cells (MFCs), in which the power output increased from 167 ± 2 μW cm−2 to 214 ± 5 μW cm−2. X-ray Photoelectron Spectroscopy (XPS) was used to evaluate surface chemistry of catalysts obtained after each synthetic step. The changes in chemical composition were directly correlated with the improvements in performance. We report outstanding reproducibility in both composition and performance among the three different batches.

The effects of the synthesis steps of a platinum group metal-free (PGM-free) catalyst on the surface chemistry, morphology, and electrochemical activity in acidic and alkaline media toward the oxygen reduction reaction (ORR) were studied. Each step exhibits a positive impact on catalyst activity. In acid media, etching of the silica template is the major contributor to the enhancement of the half-wave potential, as the ORR active sites formed during the first pyrolysis become more accessible. Further processing steps result even in higher accessibility and utilization of the 4e − transfer sites. In alkaline media, the second pyrolysis is a critical step that favors the complete reduction of oxygen to water, as the peroxide production is significantly diminished. The large heterogeneity in the porosity at each synthesis step indicates that this parameter needs to be further studied to attain better control of the morphology of the PGM-free catalyst, as it is an important factor that contributes to the active site utilization. The acid etching and second pyrolysis increase the meso-and macroporosity. Understanding the effects of each of the synthesis steps on the chemical composition, morphology and ORR activity of the PGM-free catalyst provides the necessary feedback for the design of synthetic schemes that increase the catalysts' performance.