Nanostructured Catalysts for Energy Storage Application

Feng Jiao (University of Delaware)

Solar fuel production is an important technological challenge, considering that the energy of sunlight that strikes the earth's surface in an hour is sufficient to meet our energy demands for a year. Irrespective of the approach that is pursued, oxygen evolution from water is the critical reaction, because water is the only cheap, clean and abundant source that is capable of completing the redox cycle for producing either hydrogen (from H2O) or carbonaceous fuels (from CO2) on a terawatt scale. Thus, an effective catalyst for oxygen evolution via water oxidation is the key to accomplish the challenge of efficient solar energy harvesting.

Recent progress indicates that cobalt and manganese spinels could be highly efficient water oxidation catalysts. Although the origin of high activity is still unclear, it has been hypothesized that the metal sitting in the octahedral sites dominates the overall performance of spinel catalyst because of its cubane structure. Here, we will show our recent studies in mesoporous binary spinel systems, which suggest the metal sitting at the tetragonal site has huge impact on the water oxidation activity of spinel catalysts. A wide range of AB2O4 mixed oxide spinels with highly ordered mesoporous structures have been synthesized for the first time and their structures have been carefully characterized. The photocatalytic oxygen evolution activities of as-prepared samples were investigated using Ru(bpy)32+/Na2S2O8 method. The preliminary results indicate the element at tetragonal sites has significant impact on the overall photocatalytic activities.

Another topic will be discussed in the presentation is the development of rechargeable lithium air battery. Traditional battery technology is based on intercalation mechanism and no catalytic process is involved. Recent breaking-through in rechargeable lithium oxygen batteries introduces OER and ORR into battery system for the first time. After intensive screening active catalysts in the past few years, α-MnO2 have been identified as the most active electrocatalyst for both reactions, while the fundamentals of how this catalyst is involved in OER/ORR during electrochemical charging/discharging haven't yet been explored.

Because the catalyst in the electrochemical cell is in a complicated environment (gas, liquid and solid, three phases), in-situ techniques are appreciated. In this presentation, we will discuss our recent progress in using in-situ X-ray absorption techniques to monitor the oxidation state of Mn during the electrocatalytic processes at real time and to elucidate the electrocatlytic mechanism of ORR/OER on the surface of α-MnO2. We have successfully fabricated a custom electrochemical cell, which allows us to monitor the electrocatalyst structure evolution in real time when subjected to high flux synchrotron X-ray source. This represents the first attempt to utilize in-situ XAS techniques to study the mechanism of OER and ORR in an electrochemical cell at real time.

Back to Seminar Home Page

Last modified 05-February-2013 by website owner: NCNR (attn: )