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Ceria/cobalt borate hybrids as efficient electrocatalysts for water oxidation under neutral conditions.

ABSTRACT: Oxygen evolution reaction (OER) catalysts are of importance for electrochemical water splitting and fuel generation. Despite enormous efforts, the design and development of OER catalysts with high catalytic activities under neutral conditions are highly desired but still remain a great challenge. Herein, we report a room temperature chemical route to prepare xceria/cobalt borate (xCeO₂/Co-Bi) hybrids as efficient OER catalysts by tuning the molar ratio of Ce/Co (x represents the amount of CeO₂). The optimised catalyst (20CeO₂/Co-Bi hybrid) was found to exhibit remarkable OER catalytic activity with an overpotential of 453 mV at a current density of 10 mA cm^-2, Tafel slope of 120 mV dec^-1 and long-term stability in neutral medium due to its good conductivity, mass transportation and strong synergetic coupling effects, showing the potential of Co-based electrochemical materials for practical application in energy storage devices.

SUBMITTER: Zhou X

PROVIDER: S-EPMC9417256 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Ceria/cobalt borate hybrids as efficient electrocatalysts for water oxidation under neutral conditions.

Zhou Xuemei X Guo Sijia S Cai Qiran Q Huang Shaoming S

Nanoscale advances 20190719 9

Oxygen evolution reaction (OER) catalysts are of importance for electrochemical water splitting and fuel generation. Despite enormous efforts, the design and development of OER catalysts with high catalytic activities under neutral conditions are highly desired but still remain a great challenge. Herein, we report a room temperature chemical route to prepare xceria/cobalt borate (xCeO2/Co-Bi) hybrids as efficient OER catalysts by tuning the molar ratio of Ce/Co (x ...[more]

PMID: 36133558

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Project description:The development of efficient and stable earth-abundant water oxidation catalysts is vital for economically feasible water-splitting systems. Cobalt phosphate (CoPi)-based catalysts belong to the relevant class of nonprecious electrocatalysts studied for the oxygen evolution reaction (OER). In this work, an in-depth investigation of the electrochemical activation of CoPi-based electrocatalysts by cyclic voltammetry (CV) is presented. Atomic layer deposition (ALD) is adopted because it enables the synthesis of CoPi films with cobalt-to-phosphorous ratios between 1.4 and 1.9. It is shown that the pristine chemical composition of the CoPi film strongly influences its OER activity in the early stages of the activation process as well as after prolonged exposure to the electrolyte. The best performing CoPi catalyst, displaying a current density of 3.9 mA cm-2 at 1.8 V versus reversible hydrogen electrode and a Tafel slope of 155 mV/dec at pH 8.0, is selected for an in-depth study of the evolution of its electrochemical properties, chemical composition, and electrochemical active surface area (ECSA) during the activation process. Upon the increase of the number of CV cycles, the OER performance increases, in parallel with the development of a noncatalytic wave in the CV scan, which points out to the reversible oxidation of Co2+ species to Co3+ species. X-ray photoelectron spectroscopy and Rutherford backscattering measurements indicate that phosphorous progressively leaches out the CoPi film bulk upon prolonged exposure to the electrolyte. In parallel, the ECSA of the films increases by up to a factor of 40, depending on the initial stoichiometry. The ECSA of the activated CoPi films shows a universal linear correlation with the OER activity for the whole range of CoPi chemical composition. It can be concluded that the adoption of ALD in CoPi-based electrocatalysis enables, next to the well-established control over film growth and properties, to disclose the mechanisms behind the CoPi electrocatalyst activation.

Project description:A barrier to understanding the factors driving catalysis in the oxygen evolution reaction (OER) is understanding multiple overlapping redox transitions in the OER catalysts. The complexity of these transitions obscure the relationship between the coverage of adsorbates and OER kinetics, leading to an experimental challenge in measuring activity descriptors, such as binding energies, as well as adsorbate interactions, which may destabilize intermediates and modulate their binding energies. Herein, we utilize a newly designed optical spectroelectrochemistry system to measure these phenomena in order to contrast the behavior of two electrocatalysts, cobalt oxyhydroxide (CoOOH) and cobalt-iron hexacyanoferrate (cobalt-iron Prussian blue, CoFe-PB). Three distinct optical spectra are observed in each catalyst, corresponding to three separate redox transitions, the last of which we show to be active for the OER using time-resolved spectroscopy and electrochemical mass spectroscopy. By combining predictions from density functional theory with parameters obtained from electroadsorption isotherms, we demonstrate that a destabilization of catalytic intermediates occurs with increasing coverage. In CoOOH, a strong (∼0.34 eV/monolayer) destabilization of a strongly bound catalytic intermediate is observed, leading to a potential offset between the accumulation of the intermediate and measurable O2 evolution. We contrast these data to CoFe-PB, where catalytic intermediate generation and O2 evolution onset coincide due to weaker binding and destabilization (∼0.19 eV/monolayer). By considering a correlation between activation energy and binding strength, we suggest that such adsorbate driven destabilization may account for a significant fraction of the observed OER catalytic activity in both materials. Finally, we disentangle the effects of adsorbate interactions on state coverages and kinetics to show how adsorbate interactions determine the observed Tafel slopes. Crucially, the case of CoFe-PB shows that, even where interactions are weaker, adsorption remains non-Nernstian, which strongly influences the observed Tafel slope.

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Ceria/cobalt borate hybrids as efficient electrocatalysts for water oxidation under neutral conditions.

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Ceria/cobalt borate hybrids as efficient electrocatalysts for water oxidation under neutral conditions.

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