Coffee‐Waste Templating of Metal Ion‐Substituted Cobalt Oxides for the Oxygen Evolution Reaction

Abstract

A facile and scalable method using coffee waste grounds as a hard template has been developed to fabricate nanostructured Co O for the oxygen evolution reaction (OER). Co O incorporating metals with different valences (M/Co=1:4; M=Cu, Ni, Fe, Cr, and W) were also prepared with similar sheet-like structures comprising nanosized crystallites. After detailed characterization by X-ray diffraction, electron microscopy, and nitrogen sorption, the oxides were employed as OER electrocatalysts. Substitution of octahedral and tetrahedral sites of the spinel structure with divalent and trivalent transition metals (Cu, Ni, Fe, and Cr) increased the activity of Co O for the OER, whereas incorporation of hexavalent W led to formation of a second crystal phase and significantly higher electrocatalytic performance. Furthermore, this method is easily scaled up for mass production of Co O with the same nanostructure, which is highly desirable for large-scale application.

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

“…Activity enhancement due to porosity and enlargement of the surface area has been intensively studied for mesostructured cobalt‐based metal oxides applied as water oxidation catalyst . However, investigations for the ORR of these materials based on nanocasting are rare .…”

“…Other approaches quantify the surface area in‐situ by measuring the double‐layer capacitance in a suitable potential range, which is then compared to the specific capacitance of a flat surface of the same material in the same electrolyte . This strategy is a common approach for studying oxygen evolution catalysts . However, if the catalyst contains an additive like carbon in ORR studies the capacitance of the additive will influence the area assessment without contributing to the catalytically active surface area .…”

“…The cobalt‐based metal oxides are synthesized by a nanocasting procedure, where their composition is varied by the addition of another transition metal (M=Ni, Cu). Therefore, high surface areas and large pore volumes can be achieved, making them highly valuable model systems for various reactions . The resulting spinel structure and surface composition are confirmed by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and X‐ray photoelectron spectroscopy (XPS).…”

“…However, it is more likely that the divalent ions stay in the tetrahedral site and the increased activity is based on additional adsorption sites . Furthermore, incorporation of Ni 2+ and Cu 2+ can increase the charge transfer rate, as shown recently by some of us . This will have a beneficial effect on the ORR activity …”

Laser Fragmentation‐Induced Defect‐Rich Cobalt Oxide Nanoparticles for Electrochemical Oxygen Evolution Reaction

“…Moreover, theoretical calculations have revealed that tuning the electronic state of Co 3 O 4 modulates the adsorption energy of intermediate species to lower the energy barrier . This can be achieved by substitution of a foreign element (e.g., Ni, Cr, Cu), defect formation, and constructing hybrid structures . Despite the massive amount of work on developing cobalt oxide catalysts, there is still a challenge to fabricate cobalt oxide in a scalable system, which delivers nanoscale morphology with modified electrical structure for efficient OER catalysis.…”