Hydrogen & Clean Energy
Research
Independent Evaluation of Small Scale Solid Oxide Fuel Cell Systems for Power Generation
SOFC power systems have the potential to achieve greater than 60 percent efficiency. The SOFC’s operating temperature is lower than combustion-based processes and precludes the formation of Nitrogen Oxide (NOx) pollutants. The SOFC’s produce near-zero-emissions of Carbon Dioxides (CO2), gaseous pollutants, and particulates. Furthermore, SOFC power systems require approximately one-third of the amount of water relative to conventional combustion-based power systems.
Our Hydrogen and Clean Energy Center performs independent testing and evaluation of small-scale SOFC systems of 1.5KW-5 KW.
Hydrogen Production Using Solid Oxide Electrolysers
A solid oxide electrolysis cell, composed of ceramics, has two porous sponge-like electrodes sandwiching a dense solid electrolyte. Electrochemical reactions and hydrogen production take place on the internal surface of the porous electrodes. Our team is studying the internal surface of the sponge-like delicate ceramics.
We design the nano-scale coating layer that could be applied on the internal surface of the porous electrode from the as-made state-of-the-art and significantly increase their catalytic activity and durability” The ultimate goal is to see increased clean hydrogen production, a viable solution for the ongoing climate crisis.
Engineering the Cathode and Anode of Solid Oxide Fuel Cells for Increased Cell-Level Power Density and Durability
(3 Patents since the year 2015)
In comparison with the emerging protonic ceramic fuel cells, the solid oxide fuel cells (SOFCs) are nowadays commercially available with applications including stationary power supply and advanced hybrid fuel cell and engine systems that have the potential of achieving ultra-high efficiency of greater than 70 %. Nevertheless, there is an urgent need for further improvement of the SOFC performance in terms of power density and long-term stability to increase their market competencies.
We do additive implantation of electrocatalysts onto the internal surface of porous electrodes, include both the cathode and anode.
Depending on the structure/chemistry of the ALD layer applied on the cathode, ALD cathode of commercial cells, we achieved cell power density enhancement by 130 % to 380 %, induced by ALD coating LSM/YSZ or LSCF/SDC. Our ALD layer has successfully suppress Sr segregation and mitigate intrinsic degradation of LSCF cathode. ALD layer is with superior stability and presents intact ALD nanostructure after 810 h operation ~650C. ALD coated cell exhibited increased Cr-tolerance and mitigate extrinsic degradation. There is a factor over 6 increase of Cr tolerance upon electrochemical operation at ~750C induced by ALD coating.
For the Ni/YSZ anode, our work is the First ALD coating work on Ni/YSZ electrode. of commercial SOFCs, both button cells & planar cell. We Successful demonstration of 7 types of ALD layers on Ni/YSZ anode. We Demonstrated ALD coating increased both catalytic activity and conductivity of Ni/YSZ. ALD coating of Ni/YSZ anode increased the power density of the entire cell by 300 %.
Thermoelectric Oxide Materials and All Oxide Thermoelectric Generators
(3 Patents since the year 2015)
For various polycrystalline thermoelectric (TE) materials, the intergranular grain boundaries are deemed to have lower electrical conductivity and possess identical Seebeck coefficient of that of the intragrains. The approaches for improving TE performance for enhancing the electrical transport properties, especially the Seebeck coefficient, are completely lacking. Single crystal Ca3Co4O9-δ exhibited excellent TE performance and were reported with an extrapolated dimensionless thermoelectric figure of merit of 0.87 in the year 2003. However, the TE energy conversion efficiency of polycrystalline Ca3Co4O9-δ ceramics is usually only about ~30-60% of that of the single crystals.
To answer the quest of improving the TE performance of polycrystalline oxide ceramics of Ca3Co4O9-δ, we have developed a unique approach of driving dopants segregation at the grain boundaries (GBs) to dramatically increase the Seebeck Coefficient and overall energy conversion efficiency of oxide. This review exploited the impact of dopants on nanostructure and the TE performance of Ca3Co4O9-δ oxide ceramics. Pertinent results from five sets of dopants with different valence states, different ionic sizes, and large variations in the ionic mass have been condensed into this review to make a point clear that the GB can be engineered to reverse the detrimentally impact on electrical properties and provide the design domain to significantly improve the TE electrical transport properties instead. Those five sets of dopants include single dopants of monovalent potassium K+, divalent Ba2+, trivalent Bi3+, dual dopants of divalent Ba2+, trivalent Bi3+, as well as dual dopants of Bi3+ and Tb3+. The five sets of dopants constantly and consistently demonstrate that the oversized dopants segregate to the grain boundaries. The selection of two dopants with appropriate size results in the oxide ceramics with peak ZT of 0.9 at 1073K, outperforming single crystals over a wide range of temperatures.
Our work unveils the atomic structure origin of the dopants' segregation at grain boundaries, and it presents a feasible and valuable approach for treating the grain boundaries as the two-dimensional secondary phase complexion that is independently tunable to simultaneously decouple the strongly correlated physical parameters and enhance the Seebeck coefficient, electrical power factor, and ZT over a wide range of temperatures.
We are also developing the CaMnO3 based n-type oxide ceramics and all oxide thermoelectric generators.