Renewable energy solutions are crucial to combat the challenges that come with climate change – a cause I feel passionate about. Converting heat to electricity is a promising avenue towards reducing the waste of energy and the subsequent reduction of carbon dioxide emissions – a prime goal of environmental groups and Green activists in recent decades. Thermionic energy conversion (TEC) is a process in which heat gets converted into electricity by thermionic emission of electrons from a heated electrode (cathode) that are collected at a cooler electrode (anode). The resulting potential difference creates a usable electric output current. My postdoctoral research has been focused on the development of new materials and approaches to enable thermionic conversion with high efficiency. The concept is illustrated below (a) with the corresponding energy band diagram (b), and the conversion efficiency as a function of cathode temperature at different barrier indices (c).

To make this process efficient even at lower temperatures, a material is required that easily emits electrons from its surface. The property that determines how much energy is required to extract an electron is called the work function. Lower work functions facilitate the emission of electrons at lower temperatures. Reducing the work function reduces the barrier index (see above Figure) and hence, strongly increases the efficiency curve.
In this project, I developed with my collaborators at Stanford University (Profs. Roger Howe and Nickolas Melosh and Dr. Dan Riley) a new approach to achieve a record-low work function (0.7 eV) for the anode of a TEC. This was ~0.3 eV lower than the lowest experimentally verified work function to date. The anode is comprised of a semiconductor (Gallium Arsenide) with an alkaline monolayer coating which creates surface dipoles that reduce the work function. Further reduction of the work function is achieved by shining a laser onto the semiconductor that induces an additional shift in the energy structure of the material. We applied this new concept to the anode of an experimental converter to demonstrate its feasibility for future high-efficiency energy conversion applications. Our work was featured on the journal cover of ACS Energy Letters as well as Austrian news outlets. For further details, please refer to the publication.

• ArXiv:2011.10905 (2020) arXiv:2011.10905

  Discovery of materials with extreme work functions by high-throughput density functional theory and machine learning

  P. Schindler, E. R. Antoniuk, G. Cheon, Y. Zhu, and E. J. Reed

• ACS Energy Letters, 4 (2019) 2436–2443 10.1021/acsenergylett.9b01214

  Surface Photovoltage-Induced Ultralow Work Function Material for Thermionic Energy Converters

  P. Schindler^*, D. C. Riley^*, I. Bargatin, K. Sahasrabuddhe, J. W. Schwede, S. Sun, P. Pianetta, Z.-X. Shen, R. T. Howe, and N. A. Melosh

  
  ^* contributed equally

• Prof. Roger Howe – website
• Prof. Nicholas Melosh – website
• Prof. Evan Reed – website