New paper published in Advanced Sustainable Systems on the ion selectivity of MXene electrodes during electrochemical operation. The Tortoise and the Hare is a classic Aesop fable that we heard growing up. We learned that a clever strategy could win over physical advantages in any match of unequal rivals. In the day and age of MXene, this fable returns when we explore MXenes as an electrode material for ion separation. The structure of MXenes impacts ion preference, as was shown before. For example, Amir Razmjou’s team wonderfully investigated the d-layer spacing’s effect on ion selectivity (10.1016/j.memsci.2021.119752). Our work now explores the ion exchange within the nanoconfined electrolyte space provided by MXene layers. We see that monovalent ions like potassium are initially preferred – only to be replaced over time by bivalent ions, like Magnesium. MXene behaves thereby like carbon nanopores, for which such ion exchange processes during continued charging were demonstrated before, among others, by the team of Maarten Biesheuvel (10.1016/j.jcis.2012.06.022). The combination of kinetic and intrinsic ion selectivity may enable novel applications within the energy/water research nexus. However, a higher ion selectivity will have to be enabled for industrial applications.

New paper published in Nature Energy entitled “Continuous transition from double-layer to Faradaic charge storage in confined electrolytes”. Our paper explores the fascinating world from ion electrosorption transitioning towards Faradaic processes when electrolytes are nanoconfined. This work was a collaboration with several groups, espcially the team of Veronica Augustyn (NC State), Yury Gogotsi (Drexel), Patrice Simone (Toulouse) and more.

New paper published in Chemical Engineering Journal. The work with the title “Electro-assisted removal of polar and ionic organic compounds from water using activated carbon felt” was done in collaboration with the Department of Environmental Engineering at the UFZ site in Leipzig.

New paper published in Macromolecular Rapid Communications. The paper is entitled “Nanoporous block copolymer membranes with enhanced solvent resistance via UV-mediated cross-linking strategies” and was done in collaboration with the Gallei Group at Saarland University and partners at University of Freiburg and TU Darmstadt. The work is featured on the front cover of the journal.

New paper published in Advanced Energy Materials. Our work used densely carboxylated but conducting
graphene derivative (graphene acid) to enable effective operation without compromising the mechanical or chemical stability of the electrode. In our studies, we found a maximum performance of 800 mAh/g at a rate of 0.05 A/g and 174 mAh/g at 2.0 A/g. This Czech-German work was done in strong collaboration especially with the team of Aristides Bakandritsos from the Technical University of Ostrava.

New review paper published in Electrochemistry Communications. Energy-efficient technologies for the remediation of water and the generation of drinking water are essential to sustainable technologies. However, we cannot have sustainable energy technology without sustainable water remediation (and vice versa). Among many possible applications, large-scale seawater desalination is a much-needed step towards large-scale hydrogen generation via power-to-gas. However, this can only be considered sustainable when done effectively and energy-efficiently. Electrochemical desalination technologies are promising alternatives towards established methods, such as reverse osmosis or nanofiltration. In the last few years, hydrogen-driven electrochemical water purification has emerged. This joint Israeli-German review article explores the concept of desalination fuel cells and capacitive-Faradaic fuel cells for ion separation. This work was done in collaboration with the research teams of Matthew Suss and of Yuri Gendel (both at Technion, Israel).

New paper published in Cell Press Physical Science on the use of sub-nanometer pores for capacitive deionization to enable membrane-free seawater desalination. Big pores are mighty powerful when it comes to capacitive deionization (CDI). CDI is highly appreciated as a potentially energy-efficient desalination technology, rendering saline water into desalinated (potable/processable) water. However, once we move from saline media with low salt concentrations (like in brackish water regimes) towards higher salt concentrations (as you find in ordinary seawater), CDI become less attractive: the desalination capacity and charge efficiency (think of it as salt removal per invested charge) drop drastically. This issue is linked to the limited permselectivity of carbon pores commonly found in CDI electrodes. Put simply: the invested charge is not only used for adding “extra “ions into the pore (thereby: lowering the feedwater ion concentration) but also to eject ions that are already inside the pore (which basically increases the ion concentration in the effluent stream). We can address this issue by implementing an ion exchange membrane (adding costs and a more complex design) or using charge-transfer materials (giving rise to desalination batteries). But is there a way to keep low-cost, nanoporous carbon and still enable direct, membrane-free seawater desalination? The answer is a resounding YES. In our 2020 paper in Sustainable Energy & Fuels, we showed already the proof of concept of using quasi-ionophobic, and thereby permselective, carbon pores. Now, our work extends the scope and demonstrates this effect’s intricate pore size dependency. The key is a subtle play of pore size and hydrated ion diameter, which allows the pore to only uptake (extra) ions once an electric potential is applied. This work was a great collaboration with the team of Guang Feng at HUST, China, and Christian Prehal at ETH Zürich that puts together simulation and experimental work.

New paper published in Desalination with the title “Particle size distribution influence on capacitive deionization: Insights for electrode preparation”. Our work explores the particle size dispersity of commercially available activated carbon. No activated carbon powder is “perfect”, that is, every powder contains (a bit) larger and smaller particles. Size separation allows to capitalize on “one powder – several sizes” aspect. Comparing mixed-sized, small-size, and large-size activated carbon classes (of the same activated carbon powder), our work shows that large particles suffer from ion transport limitation, but so do electrodes composed of (well-packed) small particles. The best performance was found to be in the middle: a hierarchic mixture of larger and smaller activated carbon particles.