Solar Fuels: Photocatalytic Water Splitting Using a 2‐Photon Approach

While the sun provides orders of magnitude more energy than we consume on earth, it is intermittent, and thus we must have storage reservoirs for when it is dark. Plants have realized early on that storing this energy in the form of molecular fuels is quite effective. In our work, we take a similarapproach and look to use solar cells to electrolyze water into hydrogen fuel and an oxygen byproduct. Modelling has shown that to optimize photoelectrolysis efficiency, a 2 photon tandem device (back toback solar cells) should be used. The underlying principle is that one solar cell should absorb high energyphotons while the other absorbs the low energy photons. This is demonstrated in Figure 1A. While theconcept seems relatively simple, no one has yet been able to full optimize this system.2‐photon water splitting devices have many issues that need to be optimized. Both solar cells needto be optimized as well as the H₂ evolution and O₂ evolution catalysts. Figure 1B shows a diagram of ourdevice design. Furthermore all of these materials must be stable in the extremely corrosive environmentneeded for water splitting. At DTU Physics we have the critical mass which enables us to look at each oneof these issues and how to integrate them seamlessly together. In this talk I will discuss a) our optimizations of our solar cell, b) how we protect the solar cells from corrosion and c) our H₂ and O₂evolution catalysts. The talk will focus on what areas of the device we think are highly optimized and whatareas need to be improved to get us to a point where we can become highly efficient and economically competitive.