Surface oxidation/spin state determines oxygen evolution reaction activity of cobalt-based catalysts in acidic environment

Abstract

Co-based catalysts are promising candidates to replace Ir/Ru-based oxides for oxygen evolution reaction (OER) catalysis in an acidic environment. However, both the reaction mechanism and the active species under acidic conditions remain unclear. In this study, by combining surface-sensitive soft X-ray absorption spectroscopy characterization with electrochemical analysis, we discover that the acidic OER activity of Co-based catalysts are determined by their surface oxidation/spin state. Surfaces composed of only high-spin CoII are found to be not active due to their unfavorable water dissociation to form CoIII-OH species. By contrast, the presence of low-spin CoIII is essential, as it promotes surface reconstruction of Co oxides and, hence, OER catalysis. The correlation between OER activity and Co oxidation/spin state signifies a breakthrough in defining the structure-activity relationship of Co-based catalysts for acidic OER, though, interestingly, such a relationship does not hold in alkaline and neutral environments. These findings not only help to design efficient acidic OER catalysts, but also deepen the understanding of the reaction mechanism.

Ultrafine Nanoclusters Unlocked 3d–4f Electronic Ladders for Efficient Electrocatalytic Water Oxidation

“…For the Co(OH) 2 @CeO 2 sample, one electron-filled state of the d z 2 orbital is unchanged, and d yz and d x 2 − y 2 shells have different electronic configurations. Therefore, the p–d–f orbital coupling-induced QSEI results in the changes in electronic structures of the Co sites from the HS ( t 2g 5 e g 2 ) state to the LS ( t 2g 6 e g 1 ) state, which is consistent with the previously reported results. , The LS state of the Co sites in Co(OH) 2 @CeO 2 results in a lower e g occupancy, which facilitates the regulation of the binding energy of the reactants; accordingly, their catalytic efficiency is improved according to the Sabatier principle …”

“…state, which is consistent with the previously reported results. 40,41 The LS state of the Co sites in Co(OH) 2 @CeO 2 results in a lower e g occupancy, which facilitates the regulation of the binding energy of the reactants; accordingly, their catalytic efficiency is improved according to the Sabatier principle. 42 The electronic and local structures of the catalysts were studied by using X-ray absorption spectroscopy (XAS).…”

Hierarchical Porous Carbon Supported Co2P2O7 Nanoparticles for Oxygen Evolution and Oxygen Reduction in a Rechargeable Zn–Air Battery

“…Transition metals anchored on a hierarchical porous carbon matrix have been regarded as highly efficient electrocatalysts due to the merits of their easily tunable electron configuration and highly exposed active sites. − Typically, the d -block metal centers have been widely investigated for updating reduction activity via crystalline regulating, defect engineering, and metal elements tuning, due to their high surface-to-volume ratios and the presence of a multimetal atom structure. , In addition, the structure of the metal active centers can be modulated through heteroatom doping to enhance the catalytic activity and structural stability. − Furthermore, the morphology and nanoscale structure of the catalyst can be adjusted to anchor and expose metal sites at the gas/liquid/solid triphasic interface, − which facilitates the diffusion of gas molecules and the transport of O 2 to the active sites. − However, the intricate local coordination environment and the difficulty in precise structure design present a challenge in establishing effective bifunctional catalysts.…”