The objective of the proposal is to develop a solar-driven microbial electrolysis cell (solar MEC) that consists of a semiconductor nanowire-arrayed photocathode and a bacteria-colonizing anode to convert dissolved organic matter to hydrogen gas. The dissolved organic matter could be from waste streams or renewable bio-based resources. Microbial electrohydrogenesis may have several advantages over bacterial fermentation for hydrogen production, such as higher hydrogen yield, higher efficiency, and substrate diversity. However, the microbial electrohydrogenesis process in conventional MEC devices requires additional energy input in terms of an external bias, typically in a range of 0.2-1.0 V, to overcome the endothermic barrier for hydrogen generation, which adds operation cost and limits the device efficiency. The solar-driven MEC design adopts a semiconductor nanowire-arrayed photocathode to assist electron transfer from a bacteria-colonizing anode and provide photovoltage for hydrogen generation. Specifically, upon illumination, the photogenerated electrons at the semiconductor conduction band reduce protons to hydrogen, while the photogenerated holes at valence band recombine with the electrons from electrogenic bacteria cells at the anode. The semiconductor nanowire-arrayed photocathode structure offers large surface area, strong light absorption and short electron diffusion length, and is designed to enhance the light absorption and proton reduction at the cathode. Fundamental issues, such as the bioanode and photocathode materials and structure, as well as electron transfer at the bacteria/anode interface, will be systematically studied.
The research will suggest approaches to optimize device configuration with the ultimate goal of demonstrating an efficient and self-sustained solar-MEC. The new device concept developed in this proposal can be applied to other bio-inorganic hybrid devices for energy conversion applications, such as microbial fuel cells.
Broader Impacts
The proposed education plan will integrate multidisciplinary research and educational activities at University of California Santa Cruz (UCSC) and University of Wisconsin at Milwaukee (UWM). New lecture material and experiments for laboratory courses will be developed that will make use of the microbial electrolysis cell (MEC) research techniques. For example, a new MEC experiment will be developed and used in an undergraduate physical chemistry laboratory class at UCSC, and course materials based on microbial fuel cells will be incorporated into an undergraduate environmental engineering course at UWM.
Research experiences will be provided to undergraduate students from under-represented groups, recruited through NSF-sponsored Summer Undergraduate Research Fellowship (SURF) and NIH-sponsored ACCESS programs respectively. The SURF program targets college/university students, while the ACCESS program targets students at the community college level in the Santa Cruz and San Jose regions. Research experiences for high school students, coordinated through existing programs at UCSC, will be provided for students recruited through local high schools. Educational outreach activities focus on development of a website for microbial fuel cells, with content designed for the general public and high school audiences that includes graphics, cartoons, and videos.
This project aims to advance a novel bioelectrochemical technology linked to solar processes through collaborative research efforts between the University of California – Santa Cruz and Virginia Tech, involving the researchers from chemistry, material science, and engineering. The proposed technology takes advantages of microbial interaction with a solid electron acceptor/donor to generate bioenergy from low-grade substrate such as wastewater, and solar energy to overcome thermodynamic barriers of proton reduction or to benefit bioelectrochemical systems (BES) with dissolved oxygen or improved nutrient removal. During the project period, the Virginia Tech team has focused on system development, examining new electrode materials/catalysts for both anode and cathode electrodes, and exploring new synergy between BES and phototrophic processes. The major scientific outcome includes: (1) a self-biased solar microbial system is developed for hydrogen production from organic compounds; (2) new catalysts based on nano-structured carbon materials (graphene or activated carbon) are developed for either electricity generation or hydrogen production in BES, and the understanding of the key factors affecting those catalysts is obtained; (3) a new photo-BES is developed through integrating algal bioreactors into microbial fuel cells for improved the sustainability of system operation and performance. This project results in the formation of new collaboration with material scientists and biologists from Northwestern University and University of Wisconsin – Milwaukee (UWM). The results have been published in several highly impacted journals such as ACS Nano, Advanced Materials (featured as a Frontispiece), Nano Energy, and Environmental Science & Technology. A provisional patent application has been submitted. The project has trained two female graduate students (one PhD and one MSc) with dissertations, and several undergraduate students including underrepresented group. The project has provided a foundation (algae-based BES system) to form a student team for the EPA P3 National Student Competition in sustainability that won the phase I award and presented their findings in the National Sustainable Design Expo. The research team has also participated in a NSF-funded Research Experience for Teachers (RET) program located in UWM School of Engineering and Applied Science, with a focus on energy education, and hosted two science teachers from local high schools for summer research; those teachers obtained hand-on experience in laboratory research about microbial fuel cells, and incorporated the knowledge in their curriculum with additional help from UWM Education School. This project has led to formation of a startup company, HydroTech Innovations, in Milwaukee. The startup company signed an intention of initial license with University of Wisconsin - Milwaukee for one of the key findings from the project, integration of algal bioreactors into MFCs (photo-BES). The key members of the startup company participated in a NSF I-Corps project (2nd round), received entrepreneur training, and conducted extensive market discovery and customer interview.
