Researchers have created a new family of nanomaterials by alloying phosphorus with arsenic, single-atom-thick ribbons of material that are highly conductive and ideal candidates for next-generation batteries, solar cells and quantum computers. Phosphorus does not conduct electricity very well, which means that it is of little use on its own in practical applications and devices. However, researchers at University College London (UCL) found that phosphorus becomes even more useful when alloyed with arsenic.
Adam Clancy, one of the study's corresponding authors, said: "Our latest work in alloying phosphorus nanoribbons with arsenic opens up many more possibilities - particularly to improve energy storage in batteries and supercapacitors, and to enhance near-infrared detectors used in medicine."
By nanoribbons, the researchers mean one-atom-thick ribbons of phosphorus, or more precisely, phosphorene, a two-dimensional material composed of a single layer of artificially made layered black phosphorus, the most stable form of phosphorus. In 2019, researchers at UCL discovered the potential of phosphorus nanoribbons. They found that adding a layer of phosphorus nanoribbons to peroxide solar cells could allow the cells to capture more energy from the sun.
In the current study, they introduced "trace amounts" of arsenic in order to improve the conductivity of phosphorus. Crystals formed from phosphorus and arsenic flakes are mixed with lithium dissolved in -58°F (-50°C) liquid ammonia. After 24 hours, remove the ammonia and replace with organic solvent. Due to the atomic structure of the flakes, lithium ions can only move in one direction and not laterally, causing cracks to form into ribbons. Researchers have created a new family of nanomaterials: arsenic-phosphorus alloy nanoribbons (AsPNRs).
They found that arsenic-phosphorus alloy nanoribbons are highly conductive above 130K (-226°F/-140°C) while retaining the useful properties of pure phosphorus nanoribbons. A key characteristic of AsPNRs is their extremely high "hole mobility." Holes are the reverse partners of electrons in electron transport, so increasing hole mobility (a measure of how quickly holes move through a material) can help increase the efficiency of current transfer.
Currently, phosphorus nanoribbons need to be mixed with conductive materials such as carbon to be used as anode materials in lithium-ion or sodium-ion batteries. The researchers said that because AsPNRs can improve the battery's energy storage capacity and charge and discharge speed, it can eliminate the need for carbon fillers. In addition, they say that using AsPNRs in solar cells will improve the flow of charge through the device, thereby increasing the efficiency of the cells.
"The arsenic-phosphorus ribbons are also magnetic, and we think the magnetism comes from the atoms along the edges, making them potentially useful in quantum computers as well," Clancy said. "More broadly, this study shows that alloying is a powerful tool for controlling the properties of this growing family of nanomaterials, and therefore their applications and potential."
The researchers say their AsPNRs can be produced on a large scale in a liquid, which can then be used in a variety of applications at low cost.
The research was published in the Journal of the American Chemical Society.