(Image source: iStock)
Helpful holes in hematite
Electrons are well-known (negative) charge carriers, indispensable in our daily lives, but they do not play this role alone. When an electron leaves its assigned place, it leaves behind a hole that can effectively behave like a positive charge carrier, provided that the electron and hole remain separated and do not recombine. In modern semiconductor electronics, holes are important charge carriers, without which devices like batteries, capacitors, fuel cells, solar cells, and PEC could not operate. PEC electrodes typically form electron-hole pairs when struck by sunlight. In PEC photoanodes made of hematite, the generated holes must diffuse to the semiconductor surface, where they can oxidize water and form oxygen.
Not all holes are created equalIn a recent study published in the «Journal of Physical Chemistry C», Empa researchers Artur Braun and Debajeet Bora and their colleagues from EPF Lausanne, the University of Basel, China and the US studied the nature of photoelectrically generated holes in a PEC that had been specially designed for gathering data while the cell is in operation («operando»). They recorded soft X-ray absorption spectra under simulated sunlight and in the dark and identified two new spectral signatures corresponding to two different hole transitions, an O 2p hole transition into the charge-transfer band and an Fe 3d-type hole transition into the upper Hubbard band. According to Braun, this is the first time that the electronic structure of a PEC photoanode has been analyzed while it was in real water splitting action, i.e. in contact with electrolyte, under anodic bias and illuminated by visible light. «The preparations for this extremely complex experiment took us three years», says Braun. «After all, soft X-ray spectroscopy works only in ultra-high vacuum, and photoelectrochemistry works only in liquids. Combining both was technically a great advancement. Yet, I would say we were very fortunate to discover the two electron holes in an operating PEC.»
Artur Braun | EurekAlert!
Spider silk key to new bone-fixing composite
20.04.2018 | University of Connecticut
Diamond-like carbon is formed differently to what was believed -- machine learning enables development of new model
19.04.2018 | Aalto University
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
23.04.2018 | Earth Sciences
23.04.2018 | Trade Fair News
23.04.2018 | Information Technology