Yi Xie is exploring how defects in very thin materials can efficiently harness energy. Credit: Robert Brook/Science Photo Library/Getty Images
A team led by Yi Xie is exploring the potential of 2D materials to change how we harness energy using photocatalytic and electrocatalytic reactions, and thermoelectric conversion, among other things.
“In 2016, we proposed that energy conversion could be optimized via defects in the electron and phonon structures of very thin, or 2D, semiconductors,” explains Xie. “These can activate more than one physical parameter, known as a ‘degree of freedom’, giving materials useful properties.”
For example, they have demonstrated that efficient interlayer charge release caused by dual vacancy defects and codoping can increase carrier concentration, thereby achieving high thermoelectric performance in BiCuSeO.
In a 2016 Nature paper, surface defects in nanosheets of partially-oxidized cobalt atoms were shown to be more likely to lead to methanol production from carbon dioxide at a manageable overpotential, the negative potential required to activate electroreduction.
Furthermore, they have found that the surface potholes of a tungsten trioxide nanosheet easily excited high momentum electrons to achieve photocatalytic nitrate synthesis directly from nitrogen at room temperature.
The team are also using excitons to improve photocatalysis. They showed the thinness of a low-dimensional black phosphorus semiconductor affected its exciton binding energy gap, widening its light absorption spectrum, improving efficient catalysis.
The latter could also be achieved, says Xie, through promoting the dissociation of excitons into uncorrelated electrons and holes, and in the heterojunctions between low-dimensional photocatalysts and noble metal particles.