Chemovoltaic Energy Conversion on Semiconductor Surface

The chemovoltaic effect, which involves the generation of electronic excitation through exergonic redox reactions, has emerged as a crucial phenomenon with extensive implications. This effect has been observed on metallic surfaces of Schottky junctions, offering valuable insights into the intricate dynamics of chemically active collisions and having the possibility to open new avenues for energy conversion. One particularly promising application of the chemovoltaic effect is its potential to demonstrate direct chemical energy harvesting by semiconductor solar cells.<br/>This study explores the exciting possibilities of chemovoltaic energy conversion by semiconductors and introduces the concept of an electrolyte-free fuel cell. This novel fuel cell is based on a Gallium Arsenide (GaAs) diode, specially designed to demonstrate electrochemical fuel oxidation and oxidant reduction reactions directly on its conduction and valence bands. The overarching goal is to determine if renewable chemical energy, as well as light, can be used to produce electricity efficiently and sustainably by hybrid cells.<br/>To test the viability of this concept, we developed a thermodynamic charge transfer model to explain the chemovoltaic effect of renewable fuels on semiconductor surfaces, and experimentally demonstrated the electricity generation. Our modelling results indicate that redox reactions occurring between a fuel and an oxidizer on the photovoltaic cell's surface can chemically excite the semiconductor. This excitation, in turn, triggers a splitting of the Fermi level for both the conduction and valence bands, thereby enabling the direct conversion of chemical energy into electricity. This effect is experimentally observable when the GaAs surface of a specially designed photovoltaic cell is exposed to liquid or vapor-phase methanol in the presence of oxygen or hydrogen peroxide, affirming the potential of the electrolyte-free fuel cell as a new technology in energy conversion. Excitation is also observed for H₂ and O₂ gases which are in-situ generated by splitting of water in KOH (0.05 M) solution in vicinity of the device surface using a separate potentiostat setup.<br/>Our findings not only demonstrate the feasibility of chemovoltaic energy conversion with renewable fuels but also suggest a pathway towards practical implementation. A deeper comprehension of the energy conversion process and its potential requires further endeavors in system optimization, cell design enhancement, and the exploration of pertinent materials and catalysts. The chemovoltaic fuel cell offers a unique and versatile platform for capturing energy ideally from a range of renewable chemical sources, potentially providing new solutions for the growing demand for sustainable power generation.