A comprehensive study of in-situ Nb-doping and microwave- assisted Co(OH)x cocatalyst for enhancing photoelectrochemical water splitting of hematite photoanodes Periyasamy Anushkkaran 1 , Tae Sik Koh 1 , Weon-Sik Chae 2 , Sun Hee Choi 3 , Hyun Hwi Lee 3 , Jum Suk Jang 1 1 Division of Biotechnology, Jeonbuk National University, South Korea, 2 Daegu Center, Korea Basic Science Institute, South Korea, 3 Pohang Accelerator Laboratory (PAL), Pohang University of Science and Technology (POSTECH), South Korea The growing demand for renewable, cost-effective, and energy-efficient technologies is a direct result of the rising energy demands and associated environmental issues resulting from the excessive consumption of fossil fuels. Hydrogen production through photoelectrochemical (PEC) cells is a crucial way for generating renewable energy since it utilizes solar energy to generate hydrogen by splitting water. 1,2 Hematite (α-Fe 2 O 3 ) based photoanodes have been extensively studied due to their nontoxicity, an abundance of resources, high stability in alkaline media and appropriate bandgap (~2.1 eV) that make them a viable candidate as a PEC water splitting photoanode. Nevertheless, poor charge transfer in the bulk and on the electrode surface, as well as slack water oxidation, are the major challenges to developing an efficient photoelectrode. 3,4 Herein, we propose the in-situ Nb-doped and microwave-assisted Co(OH) x cocatalyst deposited α-Fe 2 O 3 photoanode (Nb-HT/Co(OH) x ) in order to improve the conductivity and sluggish water oxidation kinetics. The photocurrent density of the as-prepared Nb-HT/Co(OH) x photoanode was 1.78 mA/cm 2 at 1.23 V vs. RHE, which is 70% higher than that of the Bare- Fe 2 O 3 photoanode. The synergistic effects of Nb-doping and Co(OH) x deposition remarkably enhanced the PEC performance by improving charge carrier mobility and donor density in hematite, as well as accelerating the interfacial charge transfer kinetics at the electrode/electrolyte interface of α-Fe 2 O 3 . The Nb-HT/Co(OH) x photoanode displayed charge separation and charge transfer efficiencies of 90% and 77.3%, respectively at 1.23 V RHE . Also, incident photon-to-current efficiency of the Nb-HT/Co(OH) x photoanode exhibited 18.4% at 400 nm at 1.23 V RHE . Additionally, the photoanode exhibited exceptional stability for a period of 10 h without any decrease. Detailed electrochemical investigations using electrochemical impedance spectroscopy, open-circuit potential, transient anodic decay and accumulated charge density techniques revealed the charge separation and transfer processes. Lastly, after 10 h continuous illumination, the Nb-HT/Co(OH) x photoanode generated 244.1 and 128 μmol of H 2 and O 2 gases, respectively. This strategy of surface modification is effectively executed on various substrates, which opens up new prospects for other photoelectrode designs in the future. References 1. T.Zhu, S. Liu, B. Huang, Q. Shao, M. Wang, F. Li, X. Tan, Y. Pi, S. C. Weng, B. Huang and Z. Hu, Energy Environ. Sci ., 2021, 14, 3194–3202. 2. S.Jiao, X. Fu, S. Wang and Y. Zhao, Energy Environ. Sci ., 2021, 14, 1722–1770. 3. H.Zhang, D. Li, W. J. Byun, X. Wang, T. J. Shin, H. Y. Jeong, H. Han, C. Li and J. S. Lee, Nat. Commun ., 2020, 11, 1–11. 4. L. K.Dhandole, P. Anushkkaran, J. B. Hwang, W. S. Chae, M. Kumar, H. H. Lee, S. H. Choi, J. S. Jang and J. S. Lee, Renew. Energy , 2022, 189, 694–703.
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