Photocatalytic hydrogen evolution coupled with organic oxidation reactions holds great potential as an alternative to water splitting for renewable energy production. However, the efficiency of this process has been limited due to the weak correlation between charge separation and surface redox reactions. In a recent research article published in Advanced Functional Materials, a team of scientists led by Qitao Chen and Yanhong Liu present a novel approach using carbon-dot-mediated photocatalysis to significantly enhance the efficiency of visible-driven hydrogen evolution coupled with organic oxidation.

The Role of Nickel Phthalocyanine in the Photocatalytic System

In this study, nickel phthalocyanine (NiPc) is employed as a key component in the photocatalytic system. NiPc serves as a highly efficient hole extractor, promoting charge separation and facilitating surface redox reactions. By modifying carbon dots (CDs) with NiPc, the researchers achieved improved electron/hole extraction as well as surface proton generation and reduction.

“Nickel phthalocyanine acts as a catalyst to efficiently extract holes, which is crucial for charge separation and subsequent reactions on the catalytic surface,” explains Dr. Baodong Mao, one of the co-authors of the study. “The incorporation of NiPc-modified carbon dots into the system significantly enhances the overall efficiency of hydrogen evolution and organic oxidation.”

The Hydrogen Evolution Rate for CIZS/NiPc-CDs

The researchers measured the hydrogen evolution rate for the Cu-In-Zn-S quantum dots (CIZS QDs) combined with NiPc-modified carbon dots (CIZS/NiPc-CDs) system. They found that the optimal hydrogen evolution rate reached an impressive 4.10 mmol g–1 h–1, a significant improvement compared to the CIZS QDs alone. This represents an 8.10-fold increase in efficiency, demonstrating the tremendous potential of this photocatalytic system.

Dr. Zhenyu Wu, another co-author of the study, explains, “The enhanced hydrogen evolution rate is attributed to the synergistic effect between the NiPc-modified carbon dots and CIZS quantum dots. The NiPc facilitates hole extraction, while the CIZS QDs contribute to efficient electron transfer, resulting in enhanced surface reactions and hydrogen generation.”

Activity Enhancement for Benzyl-Alcohol-Oxidation-Coupled H2 Evolution

One of the remarkable findings of this study is the significant activity enhancement observed when coupling benzyl alcohol oxidation with hydrogen evolution. The researchers observed a 19.54-fold increase in activity compared to traditional systems. This improvement is attributed to the efficient charge extraction and accelerated surface redox reactions facilitated by the NiPc-modified carbon dots.

“Our findings demonstrate the remarkable potential of this photocatalytic system in organic oxidation coupling reactions,” says Dr. Qitao Chen, the lead author of the study. “The high activity enhancement opens up new opportunities for using renewable resources and converting them into valuable chemicals in a more sustainable manner.”

Application to Other Oxidation Coupling Systems

The strategy developed by the research team also shows promise in other oxidation coupling systems beyond benzyl alcohol. The same significant activity enhancement was observed for methanol- and furfuryl-alcohol-oxidation coupled hydrogen evolution. This indicates the versatility and potential applicability of the NiPc-modified carbon dot system in various organic oxidation reactions.

“Our photocatalytic system offers a universal approach to improve the efficiency of organic oxidation coupling reactions,” explains Dr. Yanhong Liu, the corresponding author of the study. “By fine-tuning the catalysts and reaction conditions, we can harness renewable energy resources and realize sustainable chemical production on a broader scale.”

Light-Induced Electrocatalysis Effect in the System

The researchers observed a light-induced electrocatalysis effect consistent with the Volmer-Heyrovsky process. This observation, supported by transient photovoltage spectroscopy and apparent kinetics analysis, provides a quasiquantitative basis for understanding the balance between charge extraction and surface reactions in the photocatalytic system.

“Our study reveals a fundamental understanding of the charge transfer and surface reactions occurring during the photocatalytic process,” says Dr. Weidong Shi, a co-author of the study. “This knowledge will pave the way for designing more efficient photocatalysts and developing advanced renewable energy technologies.”

In conclusion, this research article presents a groundbreaking approach utilizing nickel phthalocyanine-modified carbon dots to enhance the efficiency of visible-driven photocatalytic hydrogen evolution coupled with organic oxidation reactions. The inclusion of NiPc in the system promotes hole extraction and facilitates surface redox reactions, resulting in significant improvements in hydrogen evolution rates and activity enhancements in various oxidation coupling systems. The light-induced electrocatalysis effect observed in the system provides valuable insights into the charge transfer and surface reactions, contributing to a better understanding of the photocatalytic process.

Source: https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202305318