Hydrogen is a key energy carrier in the green shift. But how environmentally friendly it is depends entirely on how it is produced. One of the most environmentally friendly ways is to produce hydrogen directly from sunlight and splitting of water: Photochemical hydrogen production. Unfortunately, there is a particularly large barrier for this today. The materials that are good for photochemically splitting water absorb very little sunlight. Titanium oxide is one such material and utilize only UV light. Using sunlight with these materials is therefore inefficient and expensive. The materials simply do not match well with sunlight.
In this project we turn the problem around. It is not the material that does not match the sunlight, it is the sunlight that does not match the material. Let us fix the sunlight instead. To do this, we use the principle called upconversion to convert visible sunlight to UV, which then drives the photocatalysis. Upconversion has been researched since the 1960s and is used in many technologies today. But so far no one has been able to efficiently up convert sunlight. In order to up convert sunlight, the system needs a helping hand that can absorb the sunlight and pass it on to the conversion system, a so-called sensitizer. It has proved difficult to find a sensitizer that is well suited and even less that also can be combined with the conversion material. It is her our solution lies. When we are able to combine the sensitizer with up conversion materials, it paves the way for radically new possibilities for the use of up-conversion to change light.
Good sensitizer molecules must absorb sunlight well and in addition have properties that make them easy to place in the structure where we want it. We have developed strategies for identifying, designing and characterizing such sensitizers and are in the process of characterizing the first samples.
The aim of this project is to radically improve solar hydrogen production, by developing materials that effectively turn visible light into UV light.
High energy photons can drive chemical reactions, destroy DNA and split water into its elements. Utilizing this force allows us to produce green hydrogen from light and water alone, through photocatalysts like TiO2. Green hydrogen is a core concept in EU’s Green Deal where it acts as cornerstone in decarbonizing the energy system. This usually means using renewable energy to run electrolysis of water. Solar photochemical hydrogen on the other hand eliminates the electrolysis step altogether. However, the amount of UV in sunlight is too small to effectively drive the photocatalysts directly. Decades of research have focused on increasing the photocatalysts absorption of sunlight, unfortunately often at the expense of chemical conversion efficiency. If we instead could effectively convert sunlight to UV, we can use already well-established photocatalysts like TiO2 that have a high chemical efficiency but limited utilization of sunlight. By efficient and broadband upconversion of visible sunlight to UV, SunUP will radically enhance the efficiency of solar-to-hydrogen production by combining the high hydrogen production efficiency of photocatalysts such as TiO2 with a novel sensitized upconversion nanocomposite materials.