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Electrochemistry and Electric Grid > Electrocatalysis

Electrochemical Tuning of Electronic Structures for Highly Active Electrocatalysts

Start Date: September 2014
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Investigators

Yi Cui, Department of Materials Science and Engineering, and Harold Hwang, Department of Applied Physics, Stanford University

Objective

The goal of this project is to develop catalysts for the storage and production of renewable energy. Catalysts that catalyse the hydrogen and oxygen evolution reactions, and oxygen reduction reactions will be the focus of this research.

Background

To maximize the energy efficiency of electrochemical systems, such as fuel cells, metal air batteries and water-splitters, researchers are exploring highly efficient electrocatalysts for three important chemical reactions: the hydrogen evolution reaction (HER), oxygen evolution recation (OER) and oxygen reduction reaction (ORR).1  Precious metal-based materials are the most efficient electrocatalysts for these reactions, but their scarcity and high cost make application at large scale questionable. Alternative materials based on low-cost elements have been widely investigated, but most nonprecious metal catalysts still underperform their precious metal counterparts.  It is important to develop strategies to improve the electrocatalytic activity and stability of these materials.

Approach

Figure 1

Figure 1: (a) Schematic of the lithiation of catalysts using a battery configuration in organic electrolyte. (b) Schematic of the delithiation process in organic electrolyte. (c) Schematic of electrocatalysis in aqueous solution after the Li electrochemical tuning process. (d) Galvanostatic discharge curve of Li electrochemical intercalation into molybdenum disulphide (MoS2) in organic electrolyte. The well-defined plateau represents the 2H to 1T phase transition.

Earlier work by these researchers has demonstrated that electrochemical tuning of the electronic structures of molybdenum disulfide (MoS2) and lithium transition-metal oxides (LiMO2) leads to enhanced catalytic activities for HER and OER, respectively.  In this project the researchers will tune the electronic structures of existing catalysts over a wide dynamic range of electrochemical potentials allowing exploration of better catalysts. This tuning method involves the electrochemical insertion or extraction of lithium (Li) ions into or out of catalytic materials to control electrochemical potential, crystal structure, surface structure and electronic structure over a wide range (up to a few volts) for HER, OER and ORR.

Figure 2

Figure 2: (a) Electrochemical tuning process of lithium cobalt oxide (LiCoO2). (b) The OER performances of LiCoO2 catalysts before and after electrochemical tuning.

For example, lithium cobalt oxide (LiCoO2) is a typical cathode material used in a rechargeable lithium ion battery, but it is not a good electrocatalyst for OER due to its undesirable electronic structure. Preliminary results have demonstrated that OER activity can be significantly improved by employing an electrochemical tuning process (Figure 2a).   Electrochemical results show that the delithiated LiCoO2 (De-LiCoO2) exhibits remarkably enhanced OER activity compared to that of pristine LiCoO2, in terms of both the onset overpotential and OER current-density increase rate (Figure 2b).

If successful, the proposed research might afford a step-out and game-changing technique for clean-chemical fuel generation and facilitate the reduction of greenhouse gas emissions. The proposed project is rooted in the fundamentals of materials science, electrochemistry and catalysis, and will further enhance catalysis research at Stanford.

References

[1] Walter, M. G., et al., Chem. Rev. 2010, 110, 6446
[2] Cook, T. R., et al., Chem. Rev. 2010, 110, 6474
[3] Liang, Y., et al.,  J. Am. Chem. Soc. 2013, 135, 2013.
[4] Wang, H., et al., Proc. Natl. Acad. Sci., 2013, 110, 1971-1906