Revealing the Defects in Graphene for Improving Electrochemical Sensor Efficiency
Russian scientists have recently concluded a study of the effects of defects in graphene on electron transfer at the graphene-solution interface.
The electrochemical properties of graphene, properties that make the material highly desirable and useful for applications such as biosensors, photovoltaics, and electrochemical cells, strongly depend on its chemical structure and electronic properties.
These also influence the kinetics of redox processes, and the study of the kinetics of heterogeneous electron transfer on graphene’s surface has been heightened by recent data showing the possibility of accelerating the transfer rate when structural defects such as vacancies and impurities are present.
Investigating Graphene’s Impurities
This new data comes from the research of scientists at the Moscow Institute of Physics and Technology, Skoltech, and the Russian Academy of Sciences Joint Institute for High Temperatures.
The scientists claim that their experimental calculations reportedly show that defects in graphene have the potential to substantially increase the charge transfer rate.
These calculations were carried out as part of wider research into the kinetics of an outer sphere nonadiabatic electron transfer in defective graphene, published in Electrochimica Acta in May.
Furthermore, the team says that by varying the type of defect, it is possible to selectively catalyze the electron transfer to a certain class of reagents in the solution. This may be useful for creating more efficient electrochemical sensors and electrocatalysts.
Insights on the Kinetics of Electron Transfer
The research presents a theoretical study of the kinetics of electron transfer when with various defects: Single and double vacancies, the Stone-Wales defect, nitrogen impurities, and epoxy and hydroxyl groups. All of these defects significantly affect the transfer rate, most notably the single vacancy where transfer rate was predicted to “grow by an order of magnitude relative to the defect-free graphene.”
According to the researchers, this increase should theoretically only be observed for redox processes with a standard potential of −0.2 volts to 0.3 volts.
Their calculations also demonstrated that due to the low quantum capacitance of the graphene sheet, the electron transfer kinetics can be controlled by changing the bilayer’s capacitance.
A graphic depicting defective graphene. Image credited to Daria Sokol/Moscow Institute of Physics and Technology
‘Useful’ for Electrochemical Sensor Applications
"In our calculations, we tried to establish a relation between the kinetics of heterogeneous electron transfer and the changes in the electronic properties of graphene caused by defects,” said Associate Professor Sergey Kislenko of the Department for Physics of High-Temperature Processes, MIPT.
However, the team instead discovered that introducing defects into an otherwise perfect graphene sheet can increase the density of electronic states near the Fermi level and accelerate electron transfer. "Also, depending on the kind of defect, it affects the density of electronic states across various energy regions in different ways,” he added.
The team believes that their discovery and the effects of defects on graphene could be useful for electrochemical sensor applications, depending on the kind of defect.