Tag: electrochemical cell

Superstore MXene: New proton hydration structure determined

Superstore MXene: New proton hydration structure determined

MXenes are able to store large amounts of electrical energy like batteries and to charge and discharge rather quickly like a supercapacitor. They combine both talents and thus are a very interesting class of materials for energy storage. The material is structured like a kind of puff pastry, with the MXene layers separated by thin water films. A team at HZB has now investigated how protons migrate in the water films confined between the layers of the material and enable charge transport. Their results have been published in the renowned journal Nature Communications and may accelerate the optimisation of these kinds of energy storage materials.

One of the biggest challenges for a climate-neutral energy supply is the storage of electrical energy. Conventional batteries can hold large amounts of energy, but the charging and discharging processes take time. Supercapacitors, on the other hand, charge very quickly but are limited in the amount of stored energy. Only in the last few years has a new class of materials been discussed that combines the advantages of batteries with those of supercapacitors, named pseudocapacitors.

Promising materials: Pseudocapacitors

Among pseudocapacitive materials, so-called MXenes consisting of a large family of 2D transition metal carbides and nitrides appear particularly promising. Their structure resembles a puff pastry, with the individual layers separated by a thin film of water that enables the transport of charges. Titanium carbide MXenes, especially, are conductive and their layered structure combined with highly negatively-charged hydrophilic surfaces offers a unique material in which positively charged ions such as protons can diffuse very efficiently. The MXenes used in this study were synthesized in the group of Prof. Yury Gogotsi in Drexel University, USA.

Charge transport examined

Over the last years, this property has been used to store and release energy from protons at unprecedented rates in acidic environment. It remains though unclear if the charges are mostly stored based on proton adsorption at the MXene surface or through desolvation of proton in the MXene interlayer.

Confinement effect expected

Due to its two-dimensional geometry, the 2-3 layer thick water film trapped between the MXene layers is expected to solvate protons differently from bulk water that we classically know. While this confinement effect is supposed to play a role in the fast diffusion of protons inside MXene materials, it has been impossible until now to characterise protons inside a MXene electrode during charging and discharging.

Vibrational modes analysed

The team led by Dr. Tristan Petit at HZB has now succeeded in doing this for the first time by analysing vibrational modes of protons excited by infrared light. Postdoctoral researcher Dr Mailis Lounasvuori has developed an operando electrochemical cell that she used to analyse protons and water inside titanium carbide MXenes at BESSY II during the charging and discharging processes. In the process, she also succeeded in distilling out the special signature of the protons in the confined water between the MXene layers.

Read more on the HZB website

Image: The experiment: Infrared light excites protons in the water film, which move between the Ti3C2-MXene layers. Their oscillation patterns show that they behave differently than in a thicker film of water.

Credit: © M. Künsting /HZB

New versatile spectro-electrochemical cell

New versatile spectro-electrochemical cell

Equipment improves the investigation of materials for fuel cells, batteries and electrolysers

Fossil fuels are the main source of energy in the world. However, the search for clean, renewable, and cheap energy sources has intensified recently, especially with the growing consensus that the rise in the average temperature of the planet is caused by human action. In this context, electrochemical devices, which involve reactions for the transformation of chemical energy into electrical energy, appear as a viable option to fossil fuels.

Among those available are fuel cells and batteries, capable of converting the chemical energy of molecules into electrical energy and storing it, and electrolysers capable of converting low-cost molecules into more economically attractive molecules. Thus, to improve the performance of these electrochemical devices, it is essential to understand the processes that occur between their components, more precisely in the interaction between the electrodes and the electrolyte.

For this reason, researchers from the State University of Campinas (UNICAMP), in collaboration with researchers from the Brazilian Center for Research in Energy and Materials (CNPEM) and the Federal University of São Carlos (UFSCar), developed an electrochemical cell [1] with the objective to perform various types of in situ experiments. These experiments allow direct access to the dynamics of electrochemical reactions in real time and make it possible to understand the processes that occur in the system from an atomic and molecular point of view. Hence, it is possible to optimize the materials that are part of fuel cells, batteries and electrolysers mentioned, and also of devices such as supercapacitors and electrochemical sensors, among others.

Read more on the LNLS website

Image: Figure 1: A, B) Schematic drawings of the SEC: threaded lip (1); aperture for passing the radiation beam and, in the case of a photoelectrochemical experiment, to illuminate the electrode with a solar simulator or LEDs (2); window (3); O-rings (4, 5, 17); CE (6 16); SEC body – part 1 (7); chamber for the electrolyte, the CE and the RE (8); electrolyte inlet and outlet (9, 11, 13), WE inlet (10); RE inlet (12); RE (14); CE inlet (15); bolt (18); SEC body – part 2 (19); WE (20).