Unraveling the effect of Fe-incorporation on high-performance water-splitting MIS photoanodes Kanokwan Klahan 1,2 , Gabriel Loget 2 and Pichaya Pattanasattayavong 1 1 Department of Materials Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), Rayong 21210, Thailand, 2 University of Bordeaux, Bordeaux INP, ISM, UMR CNRS 5255, F-33607 Pessac, France Si photoanodes decorated with Ni nanoparticles (NPs) are known for their high performance in photoelectrochemical (PEC) solar water splitting and have been considered model systems for the mechanistic study of inhomogeneous metal-insulator-semiconductor photoanodes. 1-4 However, the specific effects of Fe impurities on the PEC performance have been neglected despite Fe having been recognized to significantly alter the electrocatalytic activity of Ni-based materials toward water oxidation. 5 Herein, we elucidate the role of Fe in Si-based MIS photoanodes modified with Ni NPs. Our results reveal that the presence of Fe does not only affect electrocatalytic properties but also the photoanode’s junction properties and interfacial energetics. The correlation between photovoltage, Fe content and NP size is rationalized by the pinch-off effect and the change in the electronic properties of NiOOH upon Fe incorporation, inducing a considerably higher overall barrier height. We show that to achieve the previously reported high photovoltage values (up to 500 mV), 3 Fe incorporation into Ni(OH) 2 /NiOOH surrounding Ni NPs is necessary. Our findings emphasize the importance of Fe impurities in this PEC system which has always been overlooked in the past. This new knowledge is crucial for the fundamental understanding of water-splitting photoelectrodes and will lead to improvements in performance evaluation and practical applications of PEC sun-to-H 2 conversion systems. References 1. Loget, G.; Fabre, B.; Fryars, S.; Mériadec, C.; Ababou-Girard, S. Dispersed Ni nanoparticles stabilize silicon photoanodes for efficient and inexpensive sunlight-assisted water oxidation. ACS Energy Lett. 2017, 2, 569–573. 2. Oh, K.; Mériadec, C.; Lassalle-Kaiser, B.; Dorcet, V.; Fabre, B.; Ababou-Girard, S.; Joanny, L.; Gouttefangeas, F.; Loget, G. Elucidating the performance and unexpected stability of partially coated water-splitting silicon photoanodes. Energy Environ. Sci. 2018, 11, 2590–2599. 3. Laskowski, F. A. L.; Oener, S. Z.; Nellist, M. R.; Gordon, A. M.; Bain, D. C.; Fehrs, J. L.; Boettcher, S. W. Nanoscale semiconductor/catalyst interfaces in photoelectrochemistry. Nat. Mater. 2020, 19, 69–76. 4. Mathur, A.; Sert, A.; Linic, S. Common misconceptions in the analysis of photoelectrocatalysts under solar water- electrocatalyst/semiconductor critical figures of merit for functioning splitting conditions. ACS Energy Lett. 2024, 9, 4136- 4146 5. Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S. W. Nickel-Iron oxyhydroxide oxygen-evolution electrocatalysts: The role of intentional and incidental Iron incorporation. J. Am. Chem. Soc. 2014, 136, 6744–6753.
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