Straightforward Synthesis Methodology for Obtaining Excellent ORR Electrocatalysts From Biomass Residues Through a One Pot‐High Temperature Treatment Approach

Abstract Materials prepared from biomass residues are potential candidates to substitute the Pt‐based commercial electrocatalysts in oxygen reduction reaction (ORR). Although some investigations have reported activity and durability comparable to Pt/C using biomass‐derived catalysts based on Fe─N─C sites, it remains a challenge to decrease the environmental impact of the production of these materials. A straightforward procedure is developed to obtain excellentORR electrocatalysts from biomass residues which requires a single high‐temperature treatment. The final washing step is avoided by optimizing the initial amount of Fe precursor (FeC₂O₄). Besides the formation of iron oxide nanoparticles, a highly dispersed Fe phase is detected by High Angle Annular Dark Field Scanning Transmission Electron Microscopy and Energy Dispersive X‐Ray Spectroscopy (HAADF‐STEM‐XEDS) analysis as well as graphitic carbon structures. The best performance for almond shell‐based electrocatalysts is achieved for the sample containing 4.6 wt. % of Fe. The procedure developed is also applied to oceanic posidonia and eucalyptus residues, also showing excellent ORR behavior. The best sample is studied in a primary Zn‐air battery (ZAB) obtaining a maximum power density of 59 mW cm⁻² and 755 mAh gZn⁻¹ capacity.