synthesis-performance-characterizations-transition-metal-single-atom

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO<sub>2</sub> Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

Harvard University

Identification of active sites for catalytic processes has both fundamental and technological implications for rational design of future catalysts. Herein, we study the active surfaces of layered lithium cobalt oxide (LCO) for the oxygen evolution reaction (OER) using the enhancement effect of electrochemical delithiation (De-LCO). Our theoretical results indicate that the most stable (0001) surface has a very large overpotential for OER independent of lithium content. In contrast, edge sites such as the nonpolar (112̅0) and polar (011̅2) surfaces are predicted to be highly active and dependent on (de)lithiation. The effect of lithium extraction from LCO on the surfaces and their OER activities can be understood by the increase of Cosites relative to Coand by the shift of active oxygen 2p states. Experimentally, it is demonstrated that LCO nanosheets, which dominantly expose the (0001) surface show negligible OER enhancement upon delithiation. However, a noticeable increase in OER activity (∼0.1 V in overpotential shift at 10 mA cm) is observed for the LCO nanoparticles, where the basal plane is greatly diminished to expose the edge sites, consistent with the theoretical simulations. Additionally, we find that the OER activity of De-LCO nanosheets can be improved if we adopt an acid etching method on LCO to create more active edge sites, which in turn provides a strong evidence for the theoretical indication.

Identifying the Active Surfaces of Electrochemically Tuned LiCoOfor Oxygen Evolution Reaction.

Engineering active grain boundaries (GBs) in oxide-derived (OD) electrocatalysts is critical to improve the selectivity in COreduction reaction (CORR), which is becoming an increasingly important pathway for renewable energy storage and usage. Different from traditional in situ electrochemical reduction under CORR conditions, where some metal oxides are converted into active metallic phases but with decreased GB densities, here we introduce the Li electrochemical tuning (LiET) method to controllably reduce the oxide precursors into interconnected ultrasmall metal nanoparticles with enriched GBs. By using ZnO as a case study, we demonstrate that the LiET-Zn with freshly exposed GBs exhibits a CO-to-CO partial current of ∼23 mA cmat an overpotential of -948 mV, representing a 5-fold improvement from the OD-Zn with GBs eliminated during the in situ electro-reduction process. A maximal CO Faradaic efficiency of ∼91.1% is obtained by LiET-Zn on glassy carbon substrate. The CO-to-CO mechanism and interfacial chemistry are further probed at the molecular level by advanced in situ spectroelectrochemical technique, where the reaction intermediate of carboxyl species adsorbed on LiET-Zn surface is revealed.

Article	Year
Identifying the Active Surfaces of Electrochemically Tuned LiCoOfor Oxygen Evolution Reaction. Journal of the American Chemical Society\| PubMed ID: 28418250	2017
Li Electrochemical Tuning of Metal Oxide for Highly Selective COReduction. ACS nano\| PubMed ID: 28558186	2017

Haotian Wang

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