Facile Synthesis of Supported Ir-Based OER Electrocatalysts Via Sputtering

Abstract

Hydrogen has been regarded as a promising energy carrier for renewable energy systems with net zero emissions [1]. However, the vast majority of industrial hydrogen has been produced from fossil fuels with high carbon dioxide (CO2) emissions [2]. An emerging method for hydrogen production potentially free of greenhouse gas emissions (so-called green hydrogen) is water electrolysis coupled to renewable energy sources such as wind, solar, hydropower, etc [3]. Among several water electrolysis technologies, proton exchange membrane water electrolyzers (PEMWEs) are the most promising due to several inherent advantages [4]. However, the large amount of iridium (Ir) used in current PEMWEs versus the limited amount of Ir resource on earth impedes large-scale and sustainable deployment of PEMWEs [5]. Lowering the amount of Ir used to efficiently catalyze the oxygen evolution reaction (OER) at PEMWE anodes might be achieved through the development of novel electrocatalysts.One strategy to reduce the Ir content of PEMWE anodes is to put Ir onto a support. This strategy can not only reduce the Ir content by improving Ir utilization in comparison with unsupported Ir-based electrocatalysts, but also decrease the Ir packing density [6]. Low Ir packing density is required for electrocatalyst layers with low Ir-contents to be sufficiently thick to ensure robust interfaces between the electrocatalyst layer and the porous transport layer (PTL) and membrane [7]. This strategy has two critical steps: (1) finding/developing a robust support and (2) depositing Ir onto the support with desired morphology with a method that is affordable, scalable, and manufacturable [8].Here we report a one-step deposition of Ir onto nanoscale tungsten-doped titanium dioxide (W-TiO2) powders via sputtering. Characterization shows that Ir is deposited onto the surface of W-TiO2 (Figure 1) in the mixed form of metallic Ir and Ir oxides with particle sizes smaller than 2 nm. The catalyst exhibits an OER mass activity twice that of Ir black in acidic media. Powder conductivity measurements confirm that the electrocatalyst is electrically conductive (~24 S/cm) despite the low conductivity of the W-TiO2 powders (~1×10-4 S/cm). Our study suggests that sputtering is a feasible deposition method for large-scale production of supported Ir-based OER electrocatalysts. Acknowledgement. This study is sponsored by internal funding from Plug Power. The sputter was done at Exothermics Inc., 14 Columbia Dr, Amherst, NH 03031 References [1] Hydrogen for Net-Zero. In A critical cost-competitive energy vector. Edited by. Hydrogen Council, McKinsey & Company; 2021.[2] IEA (2021), Global Hydrogen Review 2021, IEA, Paris (available via the Internet at: https://www.iea.org/reports/global-hydrogen-review-2021)[3] Emonts, B., Müller, M., Hehemann, M., Janßen, H., Keller, R., Stähler, M., ... & Kasselmann, S. (2022). A Holistic Consideration of Megawatt Electrolysis as a Key Component of Sector Coupling. Energies, 15(10), 3656.[4] Zhang, K., Liang, X., Wang, L., Sun, K., Wang, Y., Xie, Z., ... & Zou, X. (2022). Status and perspectives of key materials for PEM electrolyzer. Nano Research Energy, 1(3), e9120032.[5] Mittelsteadt, C. (Invited) Ir Strangelove: Or How I Learned to Stop Worrying and Embrace the PEM. ECS Meeting s MA2022-01, 1335-1335 (2022).[6] Bernt, M., Hartig‐Weiß, A., Tovini, M. F., El‐Sayed, H. A., Schramm, C., Schröter, J., ... & Gasteiger, H. A. (2020). Current challenges in catalyst development for PEM water electrolyzers. Chemie Ingenieur Technik, 92(1-2), 31-39.[7] Bernt, M., Siebel, A., & Gasteiger, H. A. (2018). Analysis of voltage losses in PEM water electrolyzers with low platinum group metal loadings. Journal of The Electrochemical Society, 165(5), F305.[8] Jia, Q., Ghoshal, S., Li, J., Liang, W., Meng, G., Che, H., ... & Mukerjee, S. (2017). Metal and metal oxide interactions and their catalytic consequences for oxygen reduction reaction. Journal of the American Chemical Society, 139(23), 7893-7903. Figure 1