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.