New paper published in npj Materials Degradation (open access). In cooperation with the group of Frank Mücklich at Saarland University and partners, we have found that coating laser-patterned stainless-steel surfaces with carbon nanotubes (CNT) or carbon onions (CO) can create an effective solid lubrication system. By storing the particles inside the pattern, lubricant retention is improved and depletion in the contact area is prevented. In previous works, we used laser interference patterning to create line patterns with different depths and coated them with CNTs or COs. Friction tests were conducted to study the effect of structural depth on the lubricity of these surfaces, and we found that shallower textures result in lower friction coefficients. Our latest study examines the degradation of the carbon nanoparticles on substrates with different structural depths, and Raman characterization shows severe degradation of both particle types. This degradation is classified within Ferrari’s three-stage amorphization model. Electron microscopy also confirms that CNT lubricity is improved at the cost of increasing particle defectivity, while CO-derived tribofilms experience even more substantial structural degradation.

Our research team has published an article in ChemSusChem on the promising use of stable and efficient SnO₂ electrodes for degrading refractory organic pollutants in wastewater treatment. Our approach involved the preparation of Ti³⁺ self-doped urchin-like rutile TiO₂ nanoclusters (TiO_2-xNCs) on a Ti mesh substrate using hydrothermal and electroreduction methods, which served as an interlayer for the deposition of Sb-SnO₂. Our TiO_2-xNCs/Sb-SnO₂ anode exhibited a high oxygen evolution potential and strong *OH generation ability, resulting in improved degradation performance for rhodamine B, methylene blue, alizarin yellow R, and methyl orange. Our unique rutile interlayer also extended the anode lifetime sixfold due to its good lattice match with SnO₂ and three-dimensional concave-convex structure. Overall, our work highlights the importance of designing interlayer crystal forms and structures for achieving efficient and stable SnO₂ electrodes in addressing dye wastewater problems. This work was done in collaboration with our colleagues from Chongqing University.

New perspective paper published in Communications Materials. The high entropy concept is ideally suited for MXenes but also capable to be a unique tool to tailor and improve electrochemical properties in other materials.

Multiple principal element or high-entropy materials have recently been studied in the two-dimensional (2D) materials phase space. These promising classes of materials combine the unique behavior of solid-solution and entropy-stabilized systems with high aspect ratios and atomically thin characteristics of 2D materials. The current experimental space of these materials includes 2D transition metal oxides, carbides/carbonitrides/nitrides (MXenes), dichalcogenides, and hydrotalcites. However, high-entropy 2D materials have the potential to expand into other types, such as 2D metal-organic frameworks, 2D transition metal carbo-chalcogenides, and 2D transition metal borides (MBenes).

So, what is our perspective article about? We discuss the entropy stabilization from bulk to 2D systems, the effects of disordered multi-valent elements on lattice distortion and local electronic structures and elucidate how these local changes influence the catalytic and electrochemical behavior of these 2D high-entropy materials. We also provide a perspective on 2D high-entropy materials research and its challenges and discuss the importance of this emerging field of nanomaterials in designing tunable compositions with unique electronic structures for energy, catalytic, electronic, and structural applications.

This perspective paper has been the result of our collaboration with my dear friend Babak Anasori (with his team: Kartik Nemani and Brian Wyatt) from Purdue University and our team (including Mohammad Torkamanzadeh).

New paper published in the Journal of the American Ceramic Society on the synthesis of new hybrid electrode materials for Li-ion batteries (LIBs). Through controlled oxidation of layered Ti₂SnC, we were able to obtain TiO₂-SnO₂-C/carbide hybrid materials using two different methods: partial oxidation in an open-air furnace (OAF) and rapid thermal annealing (RTA). The resulting carbide phase included both residual Ti₂SnC and TiC as a reaction product. In testing, we found that the sample oxidized in the OAF at 700°C for 1 hour had the highest initial lithiation capacity of 838 mAh/g at 100 mA/g. However, its delithiation capacity decreased to 427 mAh/g over cycling. In contrast, the RTA sample treated at 800°C for 30 seconds demonstrated the most efficient performance, with a reversible capacity of approximately 270 mAh/g after 150 cycles and a specific capacity of about 150 mAh/g under high cycling rate (2000 mA/g). Our findings suggest that this processing method could have wide-ranging applications in energy storage, particularly for other members of the MAX family. This work was the latest product of collaboration with the team of Michael Naguib (Tulane University, USA).

New paper published in ChemSusChem in collaboration with the Kickelbick-Group at Saarland University. We have developed an exciting new class of inorganic-organic hybrid materials with redox-active components that have great potential for use in lithium-ion batteries (LIBs). The materials were prepared using an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD), and a low-energy continuous wet chemical synthesis process known as the microjet process. By varying the ratio of molybdate to organic ligand and pH, we were able to produce two different crystalline hybrid products with large surface areas in the submicrometer range and high purity and reproducibility on a large scale. The first product, [C₆H₁₀N₂]₂[Mo₈O₂₆] ⋅ 6 H₂O, was obtained by using a ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1. The second product, [C₆H₉N₂]₄[NH₄]₂[Mo₇O₂₄] ⋅ 3 H₂O, was obtained by using higher PPD ratios from 9 : 1 to 30 : 1. Our electrochemical testing revealed that the second product showed exceptional battery performance, with a high capacity of 1084 mAh/g at 100 mA/g after 150 cycles. The product reached maximum capacity after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li₂MoO₄ and an additional in situ polymerization of PPD. We are excited about the potential of this hybrid material for use in LIB applications.

After a lot of work by our Ph.D. students Stefanie Arnold and Lei Wang, our invited article in the Wiley journal SMALL on the dual-use of seawater batteries for energy storage and water desalination. Seawater batteries are a unique type of device that capitalizes, in the most common design, on a ceramic separator, an electrocatalytic reaction on one electrode side, and reversible sodium-ion electrochemistry on the other side. Since simple seawater can be used as the aqueous electrolyte in the system, the system has become known as seawater batteries. In our opinion, this technology can do more than contribute toward beyond-lithium energy storage by also being used for desalination.

New paper published in Electrochimica Acta on Ni-decorated AgAu alloy graphene/cobalt hydroxide electrodes for micro-supercapacitors to obtain high-performance micro-supercapacitors. A nanocomposite of graphene, cobalt hydroxide and nickel can was obtained from using gold-silver alloy lines. Using a two-step electrodeposition method, the scaly morphology is pre-deposited on a Ni film, followed by the interconnecting corrugated graphene/cobalt hydroxide composite nanomaterial. The resulting device, a graphene/cobalt hydroxide/Ni//activated carbon flexible micro-supercapacitor (MSC), was assembled by gel KOH-PVA electrolyte, graphene/cobalt hydroxide/Ni (positive electrode), and activated carbon (negative electrode). When testing, we obtained a volumetric energy of about 19 mWh/cm³ and the devices retained over 94% capacitance after 10,000 cycles. After 1,000 continuous bending/unbending cycles at a 180° bending angle with the frequency of 100 mHz, the capacitance retention of MSC is still maintained at 97% of the initial value.

New paper published in Materials Futures. Sodium-deficient, P2-type layered oxides are promising cathodes for sodium-ion batteries. Their open sodium cation transport pathways lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 V to 4.6 V. Advanced operando techniques and post-mortem analysis were used to thoroughly probe the underlying reaction mechanism. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.

New paper published in Current Opinion in Green and Sustainable Chemistry on “Recent advances in wastewater treatment using semiconductor photocatalysts”. Can’t decide if you like water remediation or photocatalysis/semiconductors more? They both make a great match! Read about synergies and future possibilities in our latest review article in Current Opinion in Green and Sustainable Chemistry. The team of Prof. Xiao Su (Jaeyoung Hong & Ki-Hyun Cho) and I explore this interesting interfacial research – interfacial in double meaning: at the interface of fluid and solid, and at the interface of material science/electrochemistry and water research. It is exciting to explore semiconductors, for example, to target emerging contaminants, such as perfluorinated compounds.

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.