Fabrication of layered double hydroxide microcapsules mediated by cerium doping in metal–organic frameworks for boosting water splitting

Author(s): Huajie Xu ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Changfu Shan ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Xiaoxia Wu ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Mingzi Sun ⁶ ^, ⁷ ^, ⁸ ^, ⁹ , Bolong Huang ⁶ ^, ⁷ ^, ⁸ ^, ⁹ , Yu Tang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Chun-Hua Yan ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2020

Journal: Energy & Environmental Science

Publisher: Royal Society of Chemistry (RSC)

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Abstract

A one-step synthesis has been developed to fabricate layered double hydroxide microcapsules via a Ce-doping strategy in metal–organic frameworks.

Abstract

Assembly of micro-/nanocapsules holds great potential for catalysis, storage, and drug delivery due to their modifiable shell, high exposed surface area, and large accommodation space. Here, an ingenious one-step reaction strategy is presented to fabricate layered double hydroxide (LDH) microcapsules, which benefit from the oxyphilic and synergistic coordination of Ce species to stabilize the initial morphology of metal–organic frameworks (MOFs). Taking advantage of this unique superstructure, the as-prepared Ni–Fe–Ce-LDH microcapsules demonstrate excellent oxygen evolution reaction (OER) activity with an overpotential of 242 mV at 10 mA cm ⁻² and long-term durability of at least 24 h. Density functional theory (DFT) results further confirm the electronic modulation induced by the Ce doping for both subtle 3D LDH architectures and superior OER performances. This work not only provides insight into the rare-earth (RE) doping mediated crystal growth and transformation process of MOFs but also represents a facile way to fabricate the desired microcapsule superstructure by virtue of the Lewis acid property and synergistic coordination of RE-ions.

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Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: the role of intentional and incidental iron incorporation.

Lena Trotochaud, Samantha L Young, James K Ranney … (2014)

Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni(1-x)Fe(x)(OH)2/Ni(1-x)Fe(x)OOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)2 to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)2/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that β-NiOOH is less active for OER than the disordered γ-NiOOH starting material and that previous reports of increased activity for β-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through-film in situ conductivity measurements show a >30-fold increase in film conductivity with Fe addition, but this change in conductivity is not sufficient to explain the observed changes in activity. Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces. These results have significant implications for the design and study of Ni(1-x)Fe(x)OOH OER electrocatalysts, which are the fastest measured OER catalysts under basic conditions.

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Identification of highly active Fe sites in (Ni,Fe)OOH for electrocatalytic water splitting.

Daniel Friebel, Mary W Louie, Michal Bajdich … (2015)

Highly active catalysts for the oxygen evolution reaction (OER) are required for the development of photoelectrochemical devices that generate hydrogen efficiently from water using solar energy. Here, we identify the origin of a 500-fold OER activity enhancement that can be achieved with mixed (Ni,Fe)oxyhydroxides (Ni(1-x)Fe(x)OOH) over their pure Ni and Fe parent compounds, resulting in one of the most active currently known OER catalysts in alkaline electrolyte. Operando X-ray absorption spectroscopy (XAS) using high energy resolution fluorescence detection (HERFD) reveals that Fe(3+) in Ni(1-x)Fe(x)OOH occupies octahedral sites with unusually short Fe-O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra. Using computational methods, we establish that this structural motif results in near optimal adsorption energies of OER intermediates and low overpotentials at Fe sites. By contrast, Ni sites in Ni(1-x)Fe(x)OOH are not active sites for the oxidation of water.