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Author ORCID Identifier


Campus-Only Access for Five (5) Years

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program

Electrical and Computer Engineering

Year Degree Awarded


Month Degree Awarded


First Advisor

Jun Yao

Subject Categories

Electrical and Electronics


The ubiquity of ambient water, present in both gaseous and liquid forms, holds a substantial reservoir of energy that could potentially be transformed into a sustainable source of electricity for powering electronics. Utilizing renewable materials to harvest electricity from such clean energy sources can further improve sustainability. Microorganisms are omnipresent in nature and can be mass produced with renewable feedstocks. Harvesting energy from ambient water through microbial materials offers a promising avenue of clean power for self-sustained systems. In this thesis, my objective is to design innovative devices for extracting energy from two distinct water forms, gaseous and liquid, using Geobacter sulfurreducens related materials. First, we found that Geobacter sulfurreducens biofilm can function as a cohesive, flexible material without the need for further processing for long-term continuous electricity production from evaporating water and achieving energy densities surpassing those attainable with conventionally engineered materials. The harnessed useful amount of electricity becomes available to power wearable devices. Moreover, Biofilms made from different microbial species also show generic current production from water evaporation, implying the potential for additional sources of biomaterial in evaporation-based electricity generation. Second, we discovered a new phenomenon and based on it engineered a device, known as Air-gen, which can continuously harvest electricity from ambient humidity, making it literally operational anywhere (e.g., even in Sahara Desert with a RH~25%). The Air-gen is fabricated with conductive microbial protein nanowires, a ‘green’ material produced by the microorganism Geobacter sulfurreducens. It is revealed that the nanowire network forms a high density of ‘breathing’ nanopores, which can gate the passage of water molecule to build up a vertical moisture gradient out of a non-gradient ambient environment. The self-maintained moisture gradient leads to charge separation for electricity flow, and the ambient humidity constantly replenishes the charge for continuous output. The Air-gen can generate a sustained (>2 months) voltage of ~0.5 V across several micrometer (μm) film thickness (>700 V/cm) in the ambient environment without decay which can provide continuous current to connected devices. Multiple Air-gen devices can be connected to charge a capacitor to power up electronics. Result from prototyped devices yields an estimated power density >3.5 kW/m3, which outperforms a number of technologies including solar cells in terms of areal density. The sustainability was further demonstrated by integrating the devices into neuromorphic interfaces for self-sustainability in the ambient environment. Third, we demonstrated that Air-gen constitutes a generic effect which can be applied to a broad range of inorganic, organic, and biological materials. The common feature of these materials is that they are engineered with appropriate nanopores to allow air water to pass through and undergo dynamic adsorption–desorption exchange at the porous interface, resulting in surface charging. Finally, we also explode the application of self-powered sensor based on protein nanowires. In summary, two types of devices utilizing microbial materials have been developed to efficiently capture electricity from ubiquitous gaseous and liquid water sources on the earth. They complement each other and can be deployed virtually anywhere, ensuring continuous energy harvesting. This transcends the inherent intermittent limitations in existing harvesters bound by specific times or locations, offering a possible ‘greener’ way to harvest energy in the future.


Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.