Enhancing water oxidation performance of carbon nitride photoanode by regulating film growth and self-engineered Z-scheme heterojunctions Abraham Solomon Kasa 1,2,3 , Vishal Jose 1,2,3 , Lakshman Sundar Arumugam 4 , Anja Vanleenhove 5 , Thierry Conard 5 , Daniely Santos 1,2,3 , Jan D’Haen 1 , Laurence Lutsen 1 , Javier E. Durantini 4 , Sixto Giménez 4 , Guy Brammertz 1,2,3 , Sudhanshu Shukla 1,2,3 , Bart Vermang 1,2,3 1 Hasselt University, Imo-imomec, Martelarenlaan 42, 3500 Hasselt, Belgium, 2 EnergyVille, Thor Park 8320, 3600 Genk, Belgium, 3 Imec, Imo-imomec, Thor Park 8320, 3600 Genk, Belgium, 4 Institute of Advanced Materials (INAM), Universitat Jaume I, Av. Vicente Sos Baynat s/n., 12006 Castellón, Spain, 5 IMEC, 3001 Leuven, Belgium Photoelectrochemical (PEC) solar energy conversion is a promising technology to address the growing global energy demand,which is projected to exceed 30 TW by 2050, approximately twice the current supply. [1] This approach enables the replacement of polluting and non-renewable energy sources with clean, sustainable, and cost-effective energy harvested directly from sunlight. [2] Carbon nitride (CN) has emerged as a promising inorganic and environmentally friendly semiconductor for driving photoelectrochemical reactions, owing to its excellent chemical and thermal stability, low cost, and favorable optical and electronic properties. [3,4] However, its practical implementation is hindered by low photoactivity compared to inorganic photoanodes due to moderate light-harvesting properties, high charge recombination rates, and sluggish charge transfer. Here, we report CN photoanodes with photoelectrochemical water splitting performance comparable to state-of-the-art materials. The CN photoanodes were prepared by a simple and scalable method involving direct deposition of carbon nitride monomers onto FTO substrates, followed by high-temperature calcination with various powder precursors. Incorporating powder precursors during the thermal polymerization led to favorable morphological modifications, improved structural ordering, and reduced charge transfer resistance. The powder-assisted growth using thiourea significantly enhances the PEC performance, with a threefold increase in photocurrent density. Further optimizing the thickness by tuning the concentration of the thiourea solution enhanced the overall PEC properties. These enhancements are attributed to improved charge separation and charge transfer efficiencies, as well as the formation of a Z-scheme heterojunction between the CN and SnS 2 layers on the FTO substrate, which facilitates more efficient charge carrier dynamics. The optimum CN photoanode achieved an excellent charge extraction efficiency and a benchmark photocurrent density of 2.7 mA cm-² at 1.23 V vs. RHE in a neutral 0.1 M Na 2 SO 4 aqueous solution. This strategy advances the understanding of carbon nitride in fundamental photoelectrochemical studies and emphasizes its potential in practical solar-driven water-splitting applications. References 1. Lewis, N. S., & Nocera, D. G. (2006). Powering the planet: Chemical challenges in solar energy utilization. Proceedings of the National Academy of Sciences,103(43), 15729-15735. 2. Jin, S. (2018). What else can photoelectrochemical solar energy conversion do besides water splitting and CO2 reduction? ACS Energy Letters, 3(10), 2610-2612. 3. Wang, X., Maeda, K., Thomas, A., Takanabe, K., Xin, G., Carlsson, J. M., ... & Antonietti, M. (2009). A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nature materials, 8(1), 76-80. 4. Joseph, M., Kumar, M., Haridas, S., Subrahmanyam, C., & Remello, S. N. (2024). A review on the advancements of graphitic carbon nitride-based photoelectrodes for photoelectrochemical water splitting. Energy Advances,3(1), 30-59.
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