B.S., Nanjing University, Physics (2014)
Ph.D., Northwestern University, Applied Physics (2019)
William Chueh, Postdoctoral Faculty Sponsor
Current Research and Scholarly Interests
Dr. Xu's research focuses on a fundamental understanding of charge transport and the related electro-chemo-mechanical mechanism in mixed electronic and ionic conductors via methods of operando local multimodal characterization. This encompasses a broad class of systems in the fields such as solid oxide fuel cells, solid state batteries and memristors, with research areas including charge transport theory, interface characterization, and novel device fabrication.
Failure Mechanism in Solid State Batteries, Stanford University (11/1/2019 - Present)
Charge Transport across Single Grain Boundaries in Oxide Electrolytes, Northwestern University (9/1/2014 - 9/6/2019)
- Persistent and partially mobile oxygen vacancies in Li-rich layered oxides NATURE ENERGY 2021
- Local Multimodal Electro-Chemical-Structural Characterization of Solid-Electrolyte Grain Boundaries ADVANCED ENERGY MATERIALS 2021; 11 (10)
- Quantifying leakage fields at ionic grain boundaries using off-axis electron holography JOURNAL OF APPLIED PHYSICS 2020; 128 (21)
Variability and origins of grain boundary electric potential detected by electron holography and atom-probe tomography
2020; 19 (8): 887-+
A number of grain boundary phenomena in ionic materials, in particular, anomalous (either depressed or enhanced) charge transport, have been attributed to space charge effects. Developing effective strategies to manipulate transport behaviour requires deep knowledge of the origins of the interfacial charge, as well as its variability within a polycrystalline sample with millions of unique grain boundaries. Electron holography is a powerful technique uniquely suited for studying the electric potential profile at individual grain boundaries, whereas atom-probe tomography provides access to the chemical identify of essentially every atom at individual grain boundaries. Using these two techniques, we show here that the space charge potential at grain boundaries in lightly doped, high-purity ceria can vary by almost an order of magnitude. We further find that trace impurities (<25 ppm), rather than inherent thermodynamic factors, may be the ultimate source of grain boundary charge. These insights suggest chemical tunability of grain boundary transport properties.
View details for DOI 10.1038/s41563-020-0656-1
View details for Web of Science ID 000526218500002
View details for PubMedID 32284599
Chemical surface exchange of oxygen on CeO2-delta in an O-2/H2O atmosphere
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2017; 19 (43): 29287-29293
The chemical surface reaction rate constant controlling the change of oxidation state of undoped ceria, kChem, was measured at 1400 °C in the range of (∼0 ≤ (pH2O/atm) ≤ 0.163(9)) and (10-3.85 ≤ (pO2/atm) ≤ 10-2.86) via the electrical conductivity relaxation method. In humidified atmospheres, kChem is fully described as the sum of kChem,O2 and kChem,H2O, which are, respectively, the rate constants for oxidation by O2 and by H2O alone. Using measurements under appropriately controlled gas conditions, the total rate constant is found to follow the correlation kChem/cm s-1 = 10-(1.35±0.07) × (pO2/atm)0.72±0.02 + 10-(3.85±0.03) × (pH2O/atm)0.36±0.03 where the pO2 and pH2O values of relevance are explicitly those of the final gas condition. The results suggest that at such high temperatures, the concentrations of surface adsorbed species are too low to influence the independent reaction pathways.
View details for DOI 10.1039/c7cp05969h
View details for Web of Science ID 000414773100030
View details for PubMedID 29071321