Keywords: solar fuels (70) HZB own research (87)

Science Highlight    21.03.2016

Solar fuels:a refined protective layer for the “artificial leaf”

The illustration shows the structure of the sample: n-doped silicon layer (black), a thin silicon oxide layer (gray), an intermediate layer (yellow) and finally the protective layer (brown) to which the catalysing particles are applied. The acidic water is shown in green.
Copyright: M. Lublow

A team at the HZB Institute for Solar Fuels has developed a process for providing sensitive semiconductors for solar water splitting (“artificial leaves”) with an organic, transparent protective layer. The extremely thin protective layer made of carbon chains is stable, conductive, and covered with catalysing nanoparticles of metal oxides. These accelerate the splitting of water when irradiated by light. The team was able to produce a hybrid silicon-based photoanode structure that evolves oxygen at current densities above 15 mA/cm2. The results have now been published in Advanced Energy Materials.

The team worked with samples of silicon, an n-doped semiconductor material that acts as a simple solar cell to produce a voltage when illuminated. Materials scientist Anahita Azarpira, a doctoral student in Dr. Thomas Schedel-Niedrig’s group, prepared these samples in such a way that carbon-hydrogen chains on the surface of the silicon were formed. “As a next step, I deposited nanoparticles of ruthenium dioxide, a catalyst,” Azarpira explains. This resulted in formation of a conductive and stable polymeric layer only three to four nanometres thick. The reactions in the electrochemical prototype cell were extremely complicated and could only be understood now at HZB.

The ruthenium dioxide particles in this new process were being used twice for the first time. In the first place, they provide for the development of an effective organic protective layer. This enables the process for producing protective layers – normally very complicated – to be greatly simplified. Only then does the catalyst do its “normal job" of accelerating the partitioning of water into oxygen and hydrogen.

Organic protection layer combines excellent stability with high current densities

The silicon electrode protected with this layer achieves current densities in excess of 15 mA/cm2. This indicates that the protection layer shows good electronic conductivity, which is by no means trivial for an organic layer. In addition, the researchers observed no degradation of the cell – the yield remained constant over the entire 24-hour measurement period. It is remarkable that an entirely different material has been favoured as an organic protective layer: graphene. This two-dimensional material has been the subject of much discussion, yet up to now could only be employed for electrochemical processes with limited success, while the protective layer developed at HZB works quite well. Because the novel material could lend itself for the deposition process as well as for other applications, we are trying to acquire international protected property rights”, says Thomas Schedel-Niedrig, head of the group.


 
“Sustained Water Oxidation by Direct Electrosynthesis of Ultrathin Organic Protection Films on Silicon”, Anahita Azarpira, Thomas Schedel-Niedrig, H.-J. Lewerenz, Michael Lublow in Advanced Energy Materials DOI: 10.1002/ aenm.201502314

arö


           



You might also be interested in
  • <p>The model refers to a cubic crystal structure (pyrochlore lattice). Not only were magnetic interactions between the nearest neighbours included, but also with the next nearest neighbours (see drawing).</p>SCIENCE HIGHLIGHT      21.01.2019

    New insights into magnetic quantum effects in solids

    Using a new computational method, an international collaboration has succeeded for the first time in systematically investigating magnetic quantum effects in the well-known 3D pyrochlore Heisenberg model. The surprising finding: physical quantum phases are formed only for small spin values. [...]


  • <p class="MsoPlainText">The atmosphere can be compared to a bathtub that can only be filled to its rim if global warming is to be limited to a certain level. We could create another small outward flow with negative emissions. However, there is no way around turning off the tap.</p>NEWS      16.01.2019

    Climate change: How could artificial photosynthesis contribute to limiting global warming?

    If CO2 emissions do not fall fast enough, then CO2 will have to be removed from the atmosphere in the future to limit global warming. Not only could planting new forests and biomass contribute to this, but new technologies for artificial photosynthesis as well. An HZB physicist and a researcher at the University of Heidelberg have estimated how much surface area such solutions would require. Although artificial photosynthesis could bind CO2 more efficiently than the natural model, there are still no large modules that are stable over the long term. The team published their calculations in "Earth System Dynamics".

    [...]


  • NEWS      15.01.2019

    Two new Helmholtz Young Investigator Groups will start in 2019

    Starting in 2019, Helmholtz-Zentrum Berlin (HZB) will be establishing two new Helmholtz Young Investigator Groups and thereby strengthening its competencies in catalysis research. The Helmholtz Association will be funding each group with 150,000 euros annually over a period of five years, and HZB will be matching that sum with its own funds. [...]




Newsletter