Uniformly Dispersed Cobalt Catalyst on the Coffee Waste-Derived Carbon Support for Hydrogen Evolution Reaction

Abstract

The research interests in transition metal catalysts on carbon support have increased last decade for expensive noble metal catalyst replacement. Because those catalysts have a large surface area, good chemical stability, and are cheap and earth-abundant. Mainly structured with Co-N-C catalysts such as Cobalt (Co) nanoparticle embedded N-doped carbon, Co single-atom catalyst on carbon, etc., are highly efficient for hydrogen evolution reaction (HER) in acidic and alkaline electrolytes.Here, we report the uniformly dispersed cobalt catalysts (Co-SCC-N) on nitrogen (N)-doped spent coffee grounds (SCG) derived carbon support, which was further utilized as HER electrocatalyst. In the first step, SCG-derived carbon is synthesized by simple pyrolysis with ZnCl2. Then, the cobalt catalyst is prepared by adsorption of the complex Co ion with 1,10-phenanthroline on the SCG-derived carbon support, followed by pyrolysis at 800°C under a nitrogen atmosphere. Uniform and high dispersions of cobalt on the carbon substrate have been confirmed by scanning transmission electron microscopy (STEM) and energy dispersive X-ray (EDX) elemental mapping analysis. X-ray photoelectron spectroscopy (XPS) determined that the catalyst contained Co2+ ions and had nitrogen-doped. Also, X-ray diffraction (XRD) and Raman spectroscopy revealed carbon materials disorders, crystallinity, and no metal-related peaks that validated no metal clusters on the carbon. Electrochemical tests were examined by linear sweep voltammetry, Tafel, electrochemical impedance spectroscopy, and chronopotentiometry (CP) in alkaline and acidic electrolytes. Co-SCC-N exhibited excellent HER performance in an alkaline medium, which needed 0.246 V to reach 10 mA cm-2. And the CP test confirmed better stability at 10 mA cm-2 for 12 hours. The result recommends a simple synthesis method for uniformly dispersed metal catalysts on biomass-derived carbon support by a simple pyrolysis technique.