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Development of photoelectrochemical (PEC) systems requires, among other advances, photoelectrode materials that are both photocatalytically active and stable in harsh electrochemical environments. We have intentionally searched for a candidate photoabsorber based on co-design principles, wherein design for photoactivity is based on the ability to integrate the new material with established semiconductors and design for stability is based on the propensity for the photoabsorber to self-passivate during operation. This has led to the first synthesis and substantial development of wurtzite ZnTiN₂ as a photoabsorber. Initially, high-throughput combinatorial synthesis was used to identify the radio-frequency co-sputtering parameter space for ZnTiN₂.¹ Cation disorder in these films reduced the bandgap to ~2.0 eV, appropriate for solar fuel generation, and the ZnTiN₂ surface was found to transform to stable oxides under CO₂R-relevant electrochemical conditions. Together, these characteristics indicate that ZnTiN₂ could be used as a photoelectrode, but the optoelectronic and crystalline properties of the material would require substantial improvement before operation in PEC applications. Next, experimental integration of ZnTiN₂ with established semiconductor systems allowed us to rapidly improve the crystalline and optoelectronic properties of the sputtered ZnTiN₂ films, paving the way for high photocatalytic activity for PEC to be demonstrated using this semiconductor. We will report on materials quality advances in ZnTiN₂ thin films as well as progress toward demonstration of this material as a photoelectrode. Future work will focus on developing PEC device structures based on the improved ZnTiN₂ photoelectrode films by optimizing semiconductor properties (e.g. doping) and interfaces with surrounding device layers.

(1) Greenaway, A. L.; Ke, S.; Culman, T.; Talley, K. R.; Mangum, J. S.; Heinselman, K. N.; Kingsbury, R. S.; Smaha, R. W.; Gish, M. K.; Miller, E. M.; Persson, K. A.; Gregoire, J. M.; Bauers, S. R.; Neaton, J. B.; Tamboli, A. C.; Zakutayev, A. Zinc Titanium Nitride Semiconductor toward Durable Photoelectrochemical Applications. J. Am. Chem. Soc. 2022, 144 (30), 13673–13687. https://doi.org/10.1021/jacs.2c04241.

Co-Author(s): John Mangum (National Renewable Energy Laboratory), Sijia Ke (University of California, Berkeley), Andriy Zakutayev (National Renewable Energy Laboratory), Jeffrey Neaton (University of California, Berkeley)

Annie Greenaway

National Renewable Energy Laboratory

Appearances