By Rodney Sutherland (BME 2015)

Dr. Pu-Xian Gao, an associate professor of Materials Science & Engineering, has received a $300,000 grant from the Department of Energy’s (DOE) University Coal Research (UCR) program in support of the research efforts to design and fabricate high temperature sensors based on three-dimensional (3D) nanowire assemblies. Last year, the grant was awarded to researchers at just nine universities. This is the first time Dr. Gao, an expert in the design, synthesis, characterization, manipulation and application of hierarchical nanostructures, has received this grant.Dr. Yu Lei, an associate professor of Chemical & Biomolecular Engineering, is the co-Principal Investigator of this grant.

To participate in the UCR program, researchers must be conducting cutting-edge research alongside students who are pursuing advanced degrees in engineering, chemistry, physics, or other technical disciplines.  The competition enables both the research and development of clean coal energy science and technology and the advanced education of many young engineers who are critical to today’s engineering workforce.  In its 34 years of existence, the agency has received as many as 200 proposals in a given year from academic institutions across the nation.  More than 750 research projects have been funded. With a combined value in excess of $150 million, these projects have provided new insights into coal’s future use, and have given nearly 2,000 students invaluable experience in understanding the relevant science and technology.

In the past four years, in collaboration with Dr. Lei, Dr. Gao and his team have spearheaded an early-stage DOE-funded research effort for designing and developing a new generation of high temperature sensing materials, i.e., hierarchical metal-oxide-based composite nanostructure assemblies fashioned in 2D and 3D, for measuring the gas concentrations in-situ and real-time in combustion chambers of various advanced energy systems, primarily in the coal-based power plants.

Their latest research has suggested that selective composite nanostructuring strategy in the ordered 2D and 3D assemblies greatly enhance response, recovery, sensitivity, selectivity and stability. This strategy can be rationally achieved at high temperature by utilizing bi-modular electrical and electrochemical gas sensing.  The process may significantly improve sensing and control accuracy and efficiency in power plants, enabling more efficient energy production and utilization per ton of coal, enhancing reliability and leading to cleaner coal-based energy.

To be able to optimize the combustion environment, engineers need to know exactly what is happening in the chamber at any specific time.  Sensor devices are therefore needed to measure gas concentrations, heat and mass flux, and the degradation of materials inside the chamber.  As one might expect, the combustion chamber of a coal-based power plant is a very harsh environment to install an electronic device. 

The combustion chambers in coal-based power plants can be heated up to 1600°C and pressurized up to 1,000 PSI – conditions that would destroy commonly available, simple and inexpensive electronic devices. Even when high temperature sensing materials are used, problems may arise associated with the electrical wiring degrading in this extremely harsh environment. Optical sensors, the current high temperature sensing technology, use signals to remotely investigate important regions of the high temperature atmosphere.  The readings obtained by this method require time consuming calibrations and rely on the assumption of a homogeneous distribution of species in the chamber to extrapolate for predictions. However, realistically, no such environmental homogeneity exists in combustion chambers. Other issues with high temperature optical sensing technology include the lapse in time between data point acquisition, complex calibration of the systems, and the cost/labor involved in installing the relatively large and complex system.            

Using the new UCR grant, Dr. Gao and the team will assemble selective 3D nanowire arrays based on high temperature stable metal oxide and nitrides into miniaturized sensors that can be easily integrated within localized areas necessary for quality environmental mapping and monitoring.  These sensors, which can be deployed inside the combustion environment, will give engineers a much more realistic and reliable view of the inner workings of an active combustion chamber.  Ultimately, the developed sensor nanomaterials and devices will offer real-time mixed gas monitoring, in situ deployment and energy harvesting capabilities, with wireless data transmission and remote sensing compatibility. Due to the small size of the sensors, small engines combustion chambers could be monitored just as easily as in the large ones in power plants. These nanowire array sensors could be applied in other environments as well, such as energy harvesting/storage, petroleum refineries, and pollution control.