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Micha Ben-Naim1 Alaina Strickler1 David Palm1 Drew Higgins2 1 Laurie King1 Adam Nielander1 Thomas Jaramillo1 2

1, Chemical Engineering, Stanford University, Stanford, California, United States
2, SUNCAT Center for Interface Science and Catalysis, SLAC National Accelerator Laboratory, Menlo Park, California, United States

Photoelectrochemical (PEC) water-splitting is a promising technology that uses solar radiation to split water into hydrogen and oxygen, providing a storable form of chemical fuel to pair with intermittent renewable electricity sources1. Silicon shows promise as a small bandgap absorber material (1.1 eV) to use in tandem PEC devices1. However, pairing catalysts with semiconductors has proven difficult due to poor energetic alignments and interfaces as well as stability concerns, which are especially limited in acid2.

Many catalyst deposition techniques require high temperatures and complicated processing and are incompatible with some photoabsorber materials. Thus, we developed a spin coating procedure due to its inherently simple and versatile nature to synthesize amorphous iridium oxide and biphasic strontium iridium oxide. Material structure is probed by SEM, XPS, AES, and XRD, while electrochemical performance was measured under illumination and in the dark by cyclic voltammetry, chronoamperometry, and electrochemical impedence spectroscopy.

The addition of strontium to the catalyst gives 550 mV of photovoltage, a 100 mV improvement upon iridium oxide. By probing a facile redox couple, we show that the strontium iridium catalyst forms a more beneficial electronic interface with silicon. A comparison of the as-prepared and post-test anodes via AES demonstrates that the predominant failure mechanism is film cracking and delamination, which originates from initial film heterogeneity.

1. L. C. Seitz, Z. Chen, A. J. Forman, B. A. Pinaud, J. D. Benck, and T. F. Jaramillo: Modeling Practical Performance Limits of Photoelectrochemical Water Splitting Based on the Current State of Materials Research. ChemSusChem 7(5), 1372 (2014).
2. D. Bae, B. Seger, P. C. K. Vesborg, O. Hansen, and I. Chorkendorff: Strategies for stable water splitting via protected photoelectrodes. Chem. Soc. Rev. 46(7), 1933 (2017).

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