Project Info

Hydrogen Fuel from Sunlight and Water

Tom Furtak |tfurtak@mines.edu

Nature has evolved very effective mechanisms for converting solar energy into useful fuel through photosynthesis in green plants. In this process water and carbon dioxide are combined in a photochemical reaction, aided by organic catalysts, to yield carbohydrates and oxygen. These steps can be duplicated in the laboratory to help understand how photosynthesis works. Armed with that knowledge, scientists have discovered ways to generate, not sugar, but hydrogen, through what has been called solar water splitting. Using only water as the starting material, these methods employ photoelectrochemical action to generate hydrogen and oxygen. There has been intense interest in optimizing these processes with the objective of providing solar-driven fuel production for a hydrogen-based energy economy [1]. For example, hydrogen fuel cells would power electric vehicles without adding any carbon to the environment.
A typical embodiment of solar water splitting works as follows: Photons are absorbed in an n-type semiconductor that may be coated with an oxidation catalyst. Photo-excited carriers (electrons) in the semiconductor move into a wire connected to an inert metal (such as platinum). Both materials are immersed in an aqueous electrolyte. Oxygen bubbles are evolved on the semiconductor and hydrogen bubbles are generated on the metal. In a more efficient embodiment of the technology, the so-called Z-cell configuration, the platinum electrode is replaced with a p-type semiconductor that is also exposed to the incident light. Absorbed photons in this material lead directly to electrons that enter the electrolyte to produce hydrogen from water. The Z-cell has the advantage that an in-series “helper” voltage source is not needed (as is the case when platinum is the reduction electrode). Among the most promising n-type materials for water splitting is bismuth vanadate (BiVO_4), which we have worked with in the past [2].
The objective of this project will be to operate and optimize a solar water splitting apparatus. This will involve producing thin films of the semiconductors, operating optical excitation and measurement instrumentation, and handling a photoelectrochemical sample chamber. Initially glass and Teflon sample chambers that are on hand will be used. However, one of the project objectives will be to design and build a sample chamber optimized for water splitting using the Z-cell configuration [3]

More Information

1. Ager, J. W., Shaner, M. R., Walczak, K. A., Sharp, I. D., and Ardo, S. “Experimental Demonstrations of Spontaneous, Solar-Driven Photoelectrochemical Water Splitting” Energy Environ. Sci. 8, (2015): 2811–2824. doi:10.1039/C5EE00457H

2. Pilli, S. K., Janarthanan, R., Deutsch, T. G., Furtak, T. E., Brown, L. D., Turner, J. A., and Herring, A. M. “Efficient Photoelectrochemical Water Oxidation over Cobalt-Phosphate (Co-Pi) Catalyst Modified BiVO4/1D-WO3 Heterojunction Electrodes.” Physical Chemistry Chemical Physics : PCCP 15, no. 35 (2013): 14723–14728. doi:10.1039/c3cp52401a

3. Minggu, L. J., Wan Daud, W. R., and Kassim, M. B. “An Overview of Photocells and Photoreactors for Photoelectrochemical Water Splitting” International Journal of Hydrogen Energy 35, no. 11 (2010): 5233–5244. doi:10.1016/j.ijhydene.2010.02.133

Grand Engineering Challenge: Make solar energy economical