This Small Business Innovation Research (SBIR) Phase I project seeks to significantly advance H2 gas sensing technologies by exploring a novel nanohybrid sensing platform of SnO2 nanocrystals supported on carbon nanotubes (CNTs). The high demand of H2 as a clean energy source drives the fast growth of the H2 sensor market. Early detection of H2 is essential to the safe handling of H2, and ultimately supports the market feasibility of a hydrogen economy. Currently, no single H2 sensor technology exists that can meet the leak detection and safety features required for the widespread use of H2. Miniaturized resistive sensors based on the proposed SnO2-CNT platform are promising for H2 detection with low cost, low energy consumption, superior sensitivity at room temperature, and flexibility to realize selectivity. The broader/commercial impacts of this research are that miniaturized H2 sensors to be developed will directly benefit society by enabling secure deployment of hydrogen fuel. Combining the unique properties of novel nanomaterials with rapid progress in microelectronic device fabrication promises low-cost, novel electronic device structures that can be readily fabricated using existing microfabrication infrastructures. The major sensing materials used in this platform, CNTs and SnO2, are affordable, particularly given the small amount of materials needed for each sensor. With a pre-fabricated sensor substrate, the sensor fabrication time is on the order of minutes. The project will also train UWM graduate and undergraduate students in the areas of nanomaterials, nanodevices, and green energy.
Use of hydrogen ("H2") as a clean fuel in transportation and power generation applications has attracted enormous interest because it can potentially reduce fossil fuel consumption, and thus mitigate air pollution and greenhouse gas emissions. H2 is bountiful, colorless, and odorless. Unfortunately, H2 is also highly flammable under ambient conditions, making its use hazardous, and a threat to public safety and risk for nearby property. H2 must be reliably monitored during its production, delivery, storage, and utilization for both safety and control purposes. The lower flammability limit ("LFL") of H2 in air is 4% by volume ("4 vol.%"). Existing H2 gas sensor technologies do not meet the U.S. Department of Energy (DOE) standards necessary for a widespread H2 economy. Thus, there is a critical need for the development of highly sensitive, extremely responsive, and low-cost sensors that can detect trace amounts of H2 as a requisite for its widespread use and the public acceptance of H2 fuel. Based on DOE technical targets, if a small leak occurs, the sensor must be able to detect 25% LFL (1 vol.%) within 1 minute so that there is sufficient time for appropriate action to control the dangerous situation. For larger leaks, the sensor must be able to detect 100% LFL (4 vol.%) within 1 second, for more serious situations. Various sensor technologies have been developed to detect H2. The most common technologies are based on electrochemical oxidation of H2, catalytic bead combustible gas sensors, or the resistance/capacitance change of Pd-based materials. Considering all potential technologies for H2 sensing, some have excellent sensitivity while others have excellent selectivity, and still others are too expensive or are slow responding. There are serious limitations for existing platform technologies used for H2 detection. Moreover, no single H2 sensor technology exists that can meet the DOE leak detection and safety standards required for the widespread use of H2. During the SBIR Phase I Project, the technical and commercial feasibility has been confirmed for this novel nanohybrid sensing platform for rapid H2 detection. Research results have demonstrated significant improvement of the sensor performance to meet DOE’s technical targets (primarily response time, recovery time, and selectivity) through the use of sorted semiconducting single-walled CNTs ("SWCNTs"), optimization of sensor materials and electrodes, and creation of nanocrystal-CNT hybrids. Major accomplishments of the project are: (1) the sensitivity of the sensor to H2 is enhanced by 150%; (2) the response time of the sensor is greatly improved from 3 minutes to around 2-3 seconds; (3) the recovery time of the sensor is improved from 1 minute to 11-30 seconds; (4) the selectivity of the sensor is confirmed: sensors show no response to CH4 (1 vol.%) and a much smaller response to CO (50 ppm); (5) the sensors are stable in ambient environment for at least two months. The current sensitivity, response time, recovery time, and selectivity of the SWCNT sensor meet the DOE targets and can be further improved by optimizing the sensor structures. Another major accomplishment of the project is a journal article on the SnO2-SWCNT H2 sensor published in Nanoscale, which is a peer-reviewed journal from the Royal Society of Chemistry Publishing Company. Two graduate students and one undergraduate student were involved in the SBIR Phase I project through a subaward to UWM. The project results will enable the transfer of new nano-technological advances from the laboratory discovery and development stage, to the commercialization of a new generation of H2 sensors responding to H2 fuel cell and lead-acid battery application market needs. NanoAffix’s (NAFX’s) miniaturized high performance sensors have lower manufacturing cost, lower power consumption, and superior performance than existing competitor sensor technologies. These favorable attributes for the NAFX technology provide a competitive advantage along with significant benefit to its customers. The NAFX hybrid platform provides a radically new opportunity to engineer gas sensors with quantum-mechanical attributes. Combining the unique properties of novel nanomaterials with rapid progress in microelectronic device fabrication promises low-cost, novel electronic device structures that can be readily fabricated using existing microfabrication infrastructures. The developed H2 sensor will not only meet the needs of the H2 economy, but also provide value to the traditional lead-acid battery use and the traditional gas sensor industry. Favorable results include the following benefits: novel product responding to unmet market needs; improved public safety and lessened personal injury risk; improved efficiency and life expectancy of H2 fuel cells and lead-acid batteries; improved environmental effects; lessened dependence on imported fossil fuels.
