Nanocrystals: Are Structure, Catalysis, Conductivity related?
We revisit a decade old mystery where our room temperature prepared 8 % Cu-ceria crystallites outperforms other Cu-doped nano-ceria as a catalyst for the water-gas shift (WGS) reaction [Catalysis Today 2012]. We examine the electrical conductivity and the structural information obtained from pair distribution function (PDF) analysis of identically prepared co-precipitated nano-ceria crystallites containing 0-16 % Cu. Polaronic conductivity is observed near temperatures relevant to WGS reactions, with the maximum conductivity (2.5×10-5/W-cm, r=400 W-cm) for the best WGS performance of 8 % Cu-doped nano-ceria measured at 200ðC. Structural analysis with PDF reveals that increasing Cu content leads to smaller crystallites (~3 nm) and greater lattice parameters. The smaller crystallites mean more CeóâÃÂú on Ce sites and a decreasing activation energy for polaron conduction. An observed steady decrease in PDF peak coherence – from undoped through 16% Cu – signals progressive finer grains and a slow loss of medium-range order. Beyond 8%, the continued decline in activation energy for conductivity is offset by a decrease of the pre-exponential term, which limits overall conductivity. This work shows that nano-ceria with 8% Cu has the highest conductivity, which coincides with its optimal catalytic WGS performance. This is the first time catalytic performance is found to correlate with electrical conductivity, which may serve as a useful descriptor for the rational design and screening of novel catalysts.
Bio: After receiving a doctoral degree from the Massachusetts Institute of Technology in Materials Science and Engineering under Robert W. Balluffi, Chan joined Bell Labs NJ (later Bellcore) as a scientist before becoming an associate professor at Columbia University. Her research has covered grain boundaries and interfaces in gold and aluminum, as well as in superconducting ceramics and super-ionic conductors where boundaries play major roles in determining current flow as supercurrent and ionic-current, respectively. Understanding the boundary structures enables the discovery of solutions to improve the desired materials properties. Chan’s recent research concentrates on nano-oxide crystals, the effects of crystal-size on bond-length, stiffness, thermal expansion, heat capacity, solubility, redox potentials and phase stability. Research results impact applications in catalysis, microelectronics, gas-sensing, biomedical therapies, micro-electro-mechanics and solid-state fuel cells.
Chan is a Fellow of the American Physical Society and the American Ceramic Society.
Chan has received Dupont Faculty Award, IBM Faculty Award, BASF Award, fellowships from John Simon Guggenheim Foundation and from Tan Chin Tuan Foundation at Nanyang Technological University of Singapore, and Faculty Diversity award from Columbia University.
Chan was honored as Presidential Faculty Fellow PFF (a forerunner of Presidential Early Career Award for Scientists and Engineers) from President Clinton.