A group of Chinese and Australian researchers offers a novel method for creating CdNCN-CdS heterostructures in mild conditions, advancing solar-driven photocatalysis for hydrogen production in a study published in the KeAi journal Advanced Powder Materials.
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Photocatalytic water splitting powered by solar energy provides a sustainable way to produce hydrogen. Although researchers have investigated a variety of semiconductors, issues such as carrier recombination and bandgap limitations still exist.
The transition metal carbodiimide CdNCN exhibits promise due to its strong covalent bonding and advantageous band gap. Through quasi-crystalline transition sites, electron transport and separation are enhanced when CdNCN and CdS heterostructures are combined. The drawback, though, is that conventional CdNCN synthesis necessitates hazardous chemicals, which presents scalability challenges.
The “one-pot” synthesis method using thiourea is a significant discovery as it streamlines the process by forming [NCN]²⁻ moieties during decomposition.
By leveraging the electron-attracting characteristics of the carbodiimide group in CdNCN, we established a rapid electron transfer pathway, resulting in record-breaking hydrogen evolution efficiency without additional cocatalysts.
Shengsen Zhang, Study Co-Corresponding and Senior Author, College of Materials and Energy, South China Agricultural University
Significantly, the optimized CdNCN-CdS heterostructure outperformed previously documented CdS-based catalysts with a hydrogen evolution rate of 14.7 mmol g⁻¹ h⁻¹ when exposed to visible light.
Zhang added, “This exceptional performance stems from the creation of atomic-level N–Cd–S transition sites, which minimize electron transfer resistance and direct electrons to the CdNCN (110) plane, the optimal site for hydrogen adsorption.”
Controlling the catalyst composition by varying the Cd-to-thiourea ratio is an intriguing part of the study. The researchers verified that intermediate [NCN]²⁻ moieties bind firmly with Cd atoms, improving charge transport within the heterostructure, using in-situ spectroscopy techniques.
“The findings highlight the importance of using a green and scalable synthesis approach to overcome the challenges of semiconductor-based photocatalysis — a step toward sustainable hydrogen production,” Zhang concluded.
The National Natural Science Foundation of China (Nos. 22078118, 22274059, and 42277219) and the Natural Science Foundation of Guangdong Province, China (Nos. 2023A1515010740 and 2023A1515030131) supported the study.
Journal Reference:
Huang, T. et. al. (2024) Green and regulable synthesis of CdNCN on CdS semiconductor: Atomic-level heterostructures for enhanced photocatalytic hydrogen evolution. Advanced Powder Materials. doi.org/10.1016/j.apmate.2024.100242