Oxygen reduction reaction platinum group metal-free electrocatalysts derived from spent coffee grounds
Giovanni Zuccante, M. Acciarri, Carmelo Lo Vecchio, Irene Gatto, Vincenzo Baglio, Nicolò Pianta, Riccardo Ruffο, Luciano Navarini, Carlo Santoro
Abstract
The annual generation of coffee waste has overtaken 6 million metric tons, becoming a serious environmental problem. Herein, we report the fabrication of bimetallic electrocatalysts synthesized by 1) pyrolyzing spent coffee grounds (SCGs) at 400, 600, 800 and 1000°C, 2) activating the as-obtained char with KOH and 3) functionalizing the activated carbon with iron(II) and manganese(II) phthalocyanine. The final electrocatalysts showed a high degree of amorphousness, defectivity (increasing with temperature) and high specific surface area (up to 1820 m2 g−1). In half-cell compartment (0.1M KOH electrolyte), the top-notch material in terms of oxygen reduction reaction (ORR) activity and selectivity was CFeMn_600, which showed the same half-wave potential (E1/2) compared to Pt/C standard along with a lower peroxide production. These outstanding results could be attributed to a high surface area, a Fe-Mn synergy, and an abundance of C-N defects. The performance of CFeMn_600 as a cathode material in alkaline exchange membrane fuel cells (AEMFC) showed an open circuit voltage (OCV) of 0.890 V and power density of 30 mW cm−2. Notwithstanding, this research is one of few cases where a waste-derived electrocatalyst is tested in a real AEMFC, thus becoming a pioneer in the fuel cell study of waste-derived electrode materials.