Water coordinated on Cu(I)-based catalysts is the oxygen source in CO2 reduction to CO.

Catalytic reduction of CO2 over Cu-based catalysts can produce various carbon-based products such as the critical intermediate CO, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we develop a modified triple-stage quadrupole mass spectrometer to monitor the reduction of CO2 to CO in the gas phase online. Our experimental observations reveal that the coordinated H2O on Cu(I)-based catalysts promotes CO2 adsorption and reduction to CO, and the resulting efficiencies are two orders of magnitude higher than those without H2O. Isotope-labeling studies render compelling evidence that the O atom in produced CO originates from the coordinated H2O on catalysts, rather than CO2 itself. Combining experimental observations and computational calculations with density functional theory, we propose a detailed reaction mechanism of CO2 reduction to CO over Cu(I)-based catalysts with coordinated H2O. This study offers an effective method to reveal the vital roles of H2O in promoting metal catalysts to CO2 reduction.

An amphiprotic paper-based electrode for glucose detection based on layered carbon nanotubes with silver and polystyrene particles.

In this work, a flexible amphiprotic amino-bonded carbon nanotube-Ag nanoparticle/polystyrene (CNT-NH2-Ag/PS) paper electrode was fabricated to measure glucose in human body fluids by a combination of vacuum filtration and high temperature baking. The front side of the fabricated paper electrode was hydrophobic and conductive, whereas its back side was hydrophilic and nonconductive. In the fabrication process, the coating sequence of CNT-NH2, Ag and PS was critical to determine the performance of the resulting CNT-NH2-Ag/PS electrode besides other parameters (e.g., amount of soluble starch, PS and Ag nanoparticles, type and amount of CNT-NH2, and electrode sensing area). Based on a series of experimental observations, the possible mechanism of glucose detection on the paper electrode was proposed, in which glucose was more favorable to migrate to the hydrophilic back side of the paper and interact with the active species (e.g., O2-) on the electrode surface. The electrochemical results showed that the CNT-NH2-Ag/PS paper electrode maintained stable electrochemical properties even after five cycles of use and 60 days of storage in air. The amphiprotic paper electrode demonstrated excellent sensing performance for glucose with a linear range of 1 µM to 1000 µM, a low detection limit of 0.2 µM, and a sensitivity of 31 333.0 µA mM-1 cm-2. The fabricated paper electrode was also successfully applied to detect different levels of glucose in complex human body fluids such as saliva, urine, and serum. These features make this type of paper electrode promising for glucose measurement.