Shungite as a Catalyst Support for Highly Active Bifunctional Oxygen Electrocatalyst

Abstract

Metal-air batteries (MABs) and regenerative fuel cells (RFCs) are based on oxygen evolu-tion reaction (OER) and oxygen reduction reaction (ORR). Creating efficient bifunctional oxygen electrocatalysts to promote both OER and ORR simultaneously is highly desirable but full of great challenges. The major limitation is that active ORR catalysts are often not efficient for OER, and vice versa. Therefore, the development of novel bifunctional oxygen electrocatalyst should ensure the exhibition of high activity for both reactions. In this work, electrochemically active and stable bifunctional catalyst materials were prepared from natu-rally occurred shungite-derived carbon material doped with nitrogen, iron, and cobalt. Prior doping, the purification of raw shungite powder was optimized and the surface morphology, structure and porosity of all samples were extensively investigated by SEM, HRTEM, XRD, Raman spectroscopy, and the BET method. Bifunctional electrocatalytic activity and stabil-ity of shungite-based materials were examined toward ORR and OER in 0.1 M KOH solution by the rotation disk electrode (RDE) method. Shungite-based catalyst doped with iron and cobalt had much lower OER overpotentials compared to commercial RuO2 benchmark and the overall oxygen electroactivity parameter (ΔE) was close to that obtained for noble metal-based commercial electrocatalysts (Pt/C + RuO2). Electrochemical stability of bimetallic shungite-based catalysts examined by the chronoamperometry technique was superior to that obtained with commercial electrocatalysts. In estonian: Metall-õhk akudes (MAB) ja regeneratiivsetes kütuseelementides (RFC) on olulised hapniku eraldumisreaktsioon (OER) ja hapniku redutseerumisreaktsioon (ORR). Tõhusate bifunktsionaalsete ORR/OER katalüsaatorite loomine on suur väljakutse. Peamine piirang on see, et aktiivsed ORR-katalüsaatorid ei ole OER-i jaoks sageli efektiivsed ja vastupidi. Seetõttu peaks uudsete bifunktsionaalsete hapniku elektrokatalüsaatorite väljatöötamine ta-gama kõrge aktiivsuse mõlemale reaktsioonile. Selles bakalaureusetöös valmistati elektro-keemiliselt aktiivsed ja stabiilsed katalüsaatorid kasutades looduslikult esinevast šungiidist saadud süsinikmaterjali dopeerimist lämmastiku, raua ja koobaltiga. Eelnevalt optimeeriti šungiidipulbri puhastamisprotseduuri ning seejärel uuriti materjalide pinna morfoloogiat, struktuuri ja poorsust kasutades SEM, HRTEM, XRD, Ramani spektroskoopia ja BET mee-todit. Šungiidipõhiste materjalide bifunktsionaalset elektrokatalüütilist aktiivsust ja stabiil-sust uuriti pöörleva ketaselektroodi (RDE) meetodil ORR ja OER suhtes 0,1 M KOH lahu-ses. Raua ja koobaltiga dopeeritud šungiidipõhistel katalüsaatoritel oli OER-i ülepinge palju madalam kui kommertsiaalsel RuO2 katalüsaatoril ja hapniku elektroaktiivsuse parameeter (ΔE) oli lähedane väärismetallidel põhinevate kommertsiaalsete elektrokatalüsaatorite (Pt/C + RuO2) omale. Kronoamperomeetria meetodil uuritud bimetalsete šungiidil põhinevate ka-talüsaatorite elektrokeemiline stabiilsus oli parem võrreldes kommertsiaalsete elektrokata-lüsaatorite stabiilsusega.