As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton conductivity is crucial for the latter; protons, i.e. positively charged hydrogen ions, are formed from hydrogen, which is used to power the fuel cell. Empa physicist Artur Braun and Qianli Chen, a doctoral student at ETH Zurich, conducted neutron scattering experiments on the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institute (PSI) that document the mobility of protons in the crystal lattice. In the process, they observed that the proton movements in ceramic fuel cells obey far more complex laws than previously assumed: The movement of the protons takes place according to the so-called polaron model, as the researchers recently reported in the renowned journal Nature Communications.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton conductivity is crucial for the latter; protons, i.e. positively charged hydrogen ions, are formed from hydrogen, which is used to power the fuel cell. Empa physicist Artur Braun and Qianli Chen, a doctoral student at ETH Zurich, conducted neutron scattering experiments on the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institute (PSI) that document the mobility of protons in the crystal lattice. In the process, they observed that the proton movements in ceramic fuel cells obey far more complex laws than previously assumed: The movement of the protons takes place according to the so-called polaron model, as the researchers recently reported in the renowned journal Nature Communications.
For a long time, the polaron theory developed by the Russian physicist and eventual Nobel Prize-winner Lev Davidovich Landau in 1933 only applied to electrons. The model describes how electrons “worm” their way through a dielectric crystal and force “interfering” atoms out of position, which slows down the electrons. In other words, polarons are waves of movement in the crystal, the spread of which can be described as the trajectory of a particle. They can be deflected and reflected.
The electron polaron has long been a pillar of theoretical physics and the undisputed basis for applied model calculations in expert circles. By contrast, the existence of a hydrogen polaron – i.e. a hydrogen ion that “hops” from one position to the next – was only a speculative theory until now. Although biologists used the model of hopping hydrogen atoms to explain certain metabolic processes, solid-state physicists did not regard hydrogen polarons as a valid explanatory model.
Read more at Swiss Federal Laboratories for Materials Science and Technology (EMPA)
