Facile Synthesis of Supported Ir-Based OER Electrocatalysts Via Sputtering
Authors: Jia Qingying , Sun Qiang , Yang Fan , Soleymani Amir Peyman , Jankovic Jasna , Mittelsteadt Cortney 
Published: September 2023

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

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Figure 1