Cobalt Spinels and Delafossites as Catalysts for the Oxygen Evolution Reaction in Acidic Media

Le résumé fourni par la source

The oxygen evolution reaction (OER) is a common anodic couple in electrochemical systems given the ubiquity of employing aqueous electrolytes. In basic conditions, the OER is typically catalyzed via platinum-group-metal-free (PGM-free) electrodes, like Ni mesh and, increasingly, NiFe oxyhydroxides. In acidic conditions, however, iridium oxide is the only industrially utilized catalyst due to its combination of high activity and stability. Given the scarcity of iridium, 1 this work builds on prior efforts by the authors 2,3 in exploring the activity and stability of PGM-free Co-based oxides for catalyzing the OER in acidic conditions. This study is guided by the following questions: is the electronegativity of dopant metals correlated with the activity and stability of Co oxides in acidic and near neutral aqueous electrolyte at potentials relevant to the OER? If so, what is the mechanism behind this, particularly from an electronic structure perspective? We approach the problem from the perspective of relative contributions of ionic and covalent bonding between the metals and oxygen in the oxide lattice. 4 If the dopant metal, M, has a lower electronegativity than Co, and thus a higher difference in electronegativity with O, its bonds with O should therefore be of a more ionic nature than those of Co with O. If this assumption is true, we hypothesize that the Co–O bond should correspondingly experience an increase in covalent bonding, a phenomenon that has been discussed by Barr in other inorganic solids. 5 This increase in covalency could induce the formation of more electrophilic oxygen sites and promote activity towards the OER. 6 Herein, we begin with the sequential doping of Co 3 O 4 (spinel) and HCoO 2 (delafossite) with Mn and examine the corresponding evolution in the cyclic voltammograms (CVs) with Mn concentration. As shown in Figure 1 , the redox couples of Co shift to more positive potentials with increasing Mn concentration across both lattices. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy experiments will be performed to check that the electronic structure corroborates the hypothesis of differences in the electronic structure of Co and O. We then compare the OER activity and catalyst stability as a function of Mn concentration with the hope of determining whether the effects of Mn doping are general between the two lattices. Stability measurements will be supported with ex-situ inductively coupled plasma mass spectrometry experiments to track Co and Mn dissolution. Figure 1 . Evolution of CVs of A) Co 3 O 4 and B) HCoO 2 with increasing Mn content in 0.1 M HClO 4 on a polycrystalline Au rotating disk electrode substrate [mol% is with regards to total moles of metal, i.e., mol Mn/(mol Mn + mol Co)]. Working electrode potentials were corrected on the fly at 85% compensation followed by a 15% manual compensation afterwards. References (1) Clapp, M.; Zalitis, C. M.; Ryan, M. Perspectives on Current and Future Iridium Demand and Iridium Oxide Catalysts for PEM Water Electrolysis. Catal. Today 2023 , 420 . https://doi.org/10.1016/j.cattod.2023.114140. (2) Liu, C. P.; Vang, E. H.; Priamushko, T.; Roiron, C.; Cherevko, S.; Atanassov, P. Acidic Oxygen Evolution Reaction Activity, Stability, and Durability of Copper and/or Manganese Cobalt Oxide Spinels. ACS Catal. 2025 , 7956–7965. https://doi.org/10.1021/acscatal.5c00523. (3) Liu, C. P.; Huynh, H. D.; Atanassov, P. Stabilizing Cobalt in the Delafossite Lattice for the Acidic Oxygen Evolution Reaction. Under peer review. (4) Pauling, L. The Nature of the Chemical Bond , 3rd ed.; Cornell University Press: Ithica, 1960. (5) Barr, T. L. Modern ECSA: The Principles and Practice of X-Ray Photoelectron Spectroscopy ; CRC Press, Inc.: Boca Raton, 1994. (6) Massué, C.; Pfeifer, V.; van Gastel, M.; Noack, J.; Algara‐Siller, G.; Cap, S.; Schlögl, R. Reactive Electrophilic O I− Species Evidenced in High‐Performance Iridium Oxohydroxide Water Oxidation Electrocatalysts. ChemSusChem 2017 , 10 (23), 4786–4798. https://doi.org/10.1002/cssc.201701291. Figure 1

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.