Energy researchers from the University of New South Wales (UNSW) have reported progress in using controlled architectural design and structural engineering as a method to refine materials to simultaneously have power high and high energy density for electrochemical storage in portable devices.
The engineered material that consists of cerium oxide nanoflakes synthesized at a constant thickness and implanted with molybdenum ions at ANSTO’s Center for Accelerator Science has demonstrated promising characteristics for use as an intercalation pseudocapacitor.
Dr. Pramod Koshy, Dr. Sajjad S Mofarah, Mr. Xiaroran Zheng and their associates from the UNSW School of Materials Science and Engineering, Solid State Physics Laboratory in Bangladesh and ANSTO have reported adjustment of control and oxygen vacancies channel. formation in cerium oxide implanted with molybdenum ions to obtain an intercalated pseudocapacitance.
The results were published in the journal ACS applied materials and interfaces.
The group was building on work started in 2017. An earlier paper published in Nature Communication in 2019 describes the ultra-thin CeO for the first time2−x for pseudo-capacitive energy storage applications.
In the most recent work, researchers made structural changes to the transition metal oxide by fabricating two-dimensional nanoflakes of defect-rich cerium oxide, which are as thin as 12 nanometers on a nickel foam substrate. .
Intrinsic defects were introduced into the nanoflakes by applying reduction conditions through an N2 atmosphere.
“Our first strategy was the creation of oxygen gaps in the system using a reducing atmosphere,” explained co-first author Dr Mofarah of UNSW.
Nanoflakes have high surface-to-volume ratios and short cross-sectional paths that enhance ionic charge transfer processes.
Surface engineering was directed towards the formation of ordered oxygen vacancy channels (network of 0D point defects) which provided an atomic channel for intercalation.
The presence of stable oxygen vacancy channels with a significantly higher number of active sites in the surface and subsurface regions in the nanoflakes enhanced the capacitance.
The role of defects has been studied in the electrodeposited CeO2−x by annealing both in air or N2.
The reduction increased the gravity capacity by 77%.
Simulations using theoretical modeling validated that surface reduction leads to the formation of ordered oxygen vacancy channels.
“It wouldn’t be very efficient as a pseudocapacitor if it weren’t two-dimensional. Ideally, with an atomic-thick nanolayer, you have all the active sites to contribute to the charge/discharge process, because there’s no There is no difference between volume and surface,” Dr. Mofarah said.
Investigators used the low-energy ion implanter beamline on the Sirius Accelerator at ANSTO’s Center for Accelerator Science to implant low-energy molybdenum ions Mo6+ in two-dimensional material.
Instrumentation scientists Dr. Armand Atanacio and Dr. Madhura Manohar carried out the ion implementation process.
This is believed to be the first use of ion implantation to improve the performance of an intercalated pseudocapacitor.
“Most of the time, our accelerators are used for analysis to characterize a material. Low-energy ion implantation is different because it modifies a material, changing its surface functional properties,” said Dr Atanacio. .
The introduction of molybdenum atoms into the crystal structure generated electrons which facilitated charge transfer, improving overall electroconductivity.
“This was our second strategy to bombard the cerium oxide layer with metal ions, in this case molybdenum, to improve the conductivity of the system. It is believed that some of the cerium is removed from the system during this process,” said Dr. Koshy.
“We use little energy to be able to put low concentrations. Also, the technique does not destroy the surface,” said Dr. Koshy.
The generation of electrons did not change the energy band but facilitated enhanced electron transfer across the bandgap.
The molybdenum ion implantation and reduction processes increased the specific capacity by 133% while the retention capacity increased from 89 to 95%.
Without the architectural and structural modifications, cerium oxide would not be suitable as a pseudocapacitor, since it has a dense crystal structure that is unlayered in nature and has only two oxidation states (i.e. Ce3+ And this4+) which can switch to each other during the charge/discharge process.
“No one has seen this behavior of cerium oxide and it’s because of the structural changes we made to the material,” Dr Mofarah said.
The group intends to experiment with other ions to see if the capacity can be further improved.
Powering the future with new perovskite-related oxide-ion conductors
Sajjad S. Mofarah et al, Proton-Assisted Creation of Controllable Volumetric Oxygen Vacancies in Ultrafine CeO2−x for Pseudocapacitive Energy Storage Applications, Nature Communication (2019). DOI: 10.1038/s41467-019-10621-2
Xiaoran Zheng et al, Role of oxygen vacancy ordering and channel formation in tuning intercalation pseudocapacitance in single-ion Mo-implanted CeO2–x nanoflakes, Applied materials and ACS interfaces (2021). DOI: 10.1021/acsami.1c14484
Provided by the Australian Nuclear Science and Technology Organization (ANSTO)
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