Enhancing the activity of oxygen-evolution and chlorine-evolution electrocatalysts by atomic layer deposition of TiO₂

Creators: Finke, Cody E.; Omelchenko, Stefan T.; Jasper, Justin T.; Lichterman, Michael F.; Read, Carlos G.; Lewis, Nathan S.; Hoffmann, Michael R.

Abstract

We report that TiO₂ coatings formed via atomic layer deposition (ALD) may tune the activity of IrO₂, RuO₂, and FTO for the oxygen-evolution and chlorine-evolution reactions (OER and CER). Electrocatalysts exposed to ∼3–30 ALD cycles of TiO₂ exhibited overpotentials at 10 mA cm⁻² of geometric current density that were several hundred millivolts lower than uncoated catalysts, with correspondingly higher specific activities. For example, the deposition of TiO₂ onto IrO₂ yielded a 9-fold increase in the OER-specific activity in 1.0 M H₂SO₄ (0.1 to 0.9 mA cm_(ECSA)⁻² at 350 mV overpotential). The oxidation state of titanium and the potential of zero charge were also a function of the number of ALD cycles, indicating a correlation between oxidation state, potential of zero charge, and activity of the tuned electrocatalysts.

Additional Information

© 2018 The Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. The article was received on 12 Aug 2018, accepted on 26 Nov 2018 and first published on 14 Dec 2018. Supporting data referenced above may be found in the ESI. This work was supported by the Bill and Melinda Gates Foundation (BMGF RTTC Grants OPP1111246 and OPP1149755). Research was in part carried out at the Molecular Materials Resource Center of the Beckman Institute of the California Institute of Technology. Funding was provided to C. E. F., J. T. J., and C. G. R. by the Resnick Institute for Sustainability at Caltech. In part, this material is based upon work by S. T. O. and N. S. L. performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. C. E. F. was the primary concept generator for this work, led electrocatalyst activity, E_(ZC), and AFM data collection and analysis, and helped fabricate and characterize the electrocatalysts. S. T. O. helped to generate the concept for this work, fabricated and characterized the electrocatalysts, and helped with data analysis and experimental design. J. T. J. helped generate the concept of this work, helped design the electrochemical methodology, and helped collect electrochemical data. M. F. L. collected the XPS data and assisted in the fitting and analysis of XPS and impedance spectroscopy data. C. G. R. lead TEM characterization of the electro catalysts. C. E. F., S. T. O., and J. T. J. prepared the manuscript and N. S. L., M. R. H., M. F. L., and C. G. R. helped with its editing. All authors reviewed and contributed to the final manuscript. We would like to acknowledge Dr Katharina Urmann and Sisir Yalamanchili for help dicing Si wafers, Jingjing Jiang for help analyzing AFM data, and Azhar Carim for help with SEM, and Laleh Majari Kasmaee for help with E_(ZC) analysis. We acknowledge Prof. Stefan Zweifel and his group for foundational mentoring as well as Prof. Gretchen Hofmeister and Prof. Matt Whited for foundational chemical insight. Conflicts of interest: The authors' institution (California Institute of Technology) has filed a U.S. patent application directly relating to the work described in the paper (patent application no. US20180087164A1, filed on Sept. 28, 2017).

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