Solid electrolytes for all-solid-state batteries are generating remarkable research interest as a means to improve, their safety, stability and performance. Solid electrolytes are often polycrystalline and the effect that grain...

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Nanoceria, typically used for 'clean air' catalytic converter technologies, is the same material that could also be used as a nanomedicine. Specifically, nanoceria, which can capture, store and release oxygen, for oxidative/reductive reactions, can also be used to control oxygen content in cellular environments; as a 'nanozyme', nanoceria mimics enzymes by acting as an antioxidant agent. The computational design procedures for predicting active materials for catalytic converters can therefore be used to design active ceria nanozymes. Crucially, the ceria nanomedicine is not a molecule; rather it is a crystal and exploits its unique crystal properties.Here, we use ab initio and classical computer modelling, together with experiment, to design structures for nanoceria that maximises its nanozymetic activity. We predict that the nanomaterial should have (truncated) polyhedral or cuboidal morphologies to expose (active)CeO2 {100} surfaces. It should also contain oxygen vacancies and surface -OH species. We also show that the surface structures strongly affects the biological activity of nanoceria.Analogous to catalyst poisoning, phosphorus 'poisoning' -the interaction of nanoceria with phosphate, a common bodily electrolyteemanates from phosphate ions binding strongly to CeO2{100} surfaces, inhibiting oxygen capture and release and hence its ability to act as an nanozyme. Conversely, phosphate interaction with {111} surfaces is weak and therefore these surfaces protect the nanozyme against poisoning.The atom-level understanding presented here also illuminates catalytic processes and poisoning in 'clean-air' or fuel-cell technologies because the mechanism underpinning and exploited in each technologyoxygen capture, storage and releaseis identical.

Surface morphology is known to affect catalytic activity, as some surfaces show greater activity than others. One of the key challenges is to identify strategies to enhance the expression of such surfaces and also to prevent their disappearance over time. Here, we apply density functional theory to the catalytic material CeO2 to predict the effect of adsorbed CO2 on the morphology of the material as a function of temperature and pressure. We predict that CO2 adsorbs as surface carbonates and that the magnitude of the adsorption energy is surface dependent, following the order {100} > {110} > {111}. We show that this difference leads to selective thermodynamic enhancement of {100} surfaces as a function of CO2 partial pressure and temperature. Finally, we show how the calculated surface free energies as a function of external conditions can be deployed to predict changes in the equilibrium particle morphology. These include the prediction that ceria nanoparticles prepared in the presence of supercritical CO2 will favour enhanced cube-like morphologies.

An important challenge when attempting to identify the role of microstructure on the properties of doped energy materials is to distinguish the behaviour of each grain boundary. In this paper we describe our recent work using atomistic simulations to investigate the structure, composition and oxygen transport of gadolinium doped cerium dioxide tilt grain boundaries. We find that energy minimisation can be systematically employed to screen grain boundary structures and dopant segregation. When dopants are distributed equally across grains, molecular dynamics simulations reveal oxygen vacancies reside near dopants, resulting in higher oxygen diffusivity. Once the dopants accumulate at the grain boundaries these grain boundaries become saturated with oxygen vacancies. We see fast oxygen diffusion within the grain boundary plane, although the depletion layer, as shown via the electrostatic potential appears to block transport across the grain boundary. However, this is highly dependent on the grain boundary structure as we find striking differences of the electrostatic potential and the segregation behaviour between each of interface studied.