Scientific publications

Stable and efficient SnO2 electrodes are very promising for effectively degrading refractory organic pollutants in wastewater treatment. In this regard, we firstly prepared Ti3+ self-doped urchin-like rutile TiO2 nanoclusters (TiO2-xNCs) on a Ti mesh substrate by hydrothermal and electroreduction to serve as an interlayer for the deposition of Sb−SnO2. The TiO2-xNCs/Sb−SnO2 anode exhibited a high oxygen evolution potential (2.63 V vs. SCE) and strong ⋅OH generation ability for the enhanced amount of absorbed oxygen species. Thus, the degradation results demonstrated its good rhodamine B (RhB), methylene blue (MB), alizarin yellow R (AYR), and methyl orange (MO) removal performance, with the rate constant increased 5.0, 1.9, 1.9, and 4.7 times, respectively, compared to the control Sb−SnO2 electrode. RhB and AYR degradation mechanisms are also proposed based on the results of high-performance liquid chromatography coupled with mass spectrometry and quenching experiments. More importantly, this unique rutile interlayer prolonged the anode lifetime sixfold, given its good lattice match with SnO2 and the three-dimensional concave–convex structure. Consequently, this work paves a new way for designing the crystal form and structure of the interlayers to obtain efficient and stable SnO2 electrodes for addressing dye wastewater problems.

Optimizing the synergy between nanoporous carbons and ionic liquids can significantly enhance the energy density of supercapacitors. The highest energy density has been obtained as the size of porous carbon matches the size of ionic liquids, while it may result in slower charging dynamics and thus reduce the power density. Enhancing energy storage without retarding charging dynamics remains challenging. Herein, we designed porous electrodes by introducing an optimized horn-like entrance to the nanopore, which can concurrently improve supercapacitors’ charging dynamics and energy storage. Our results revealed the mechanism of improved charging lies in the gradual desolvation process and optimized ion motion paths: the former expedites the adsorption of the counterion by reducing the transitional energy barrier for ions entering the pores, and the latter accelerates the co-ion desorption and eliminates ion overfilling. Meanwhile, the enhancement of energy density could be attributed to the multi-ion coordinated migration.

Inorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C6H10N2]2[Mo8O26] ⋅ 6 H2O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C6H9N2]4[NH4]2[Mo7O24] ⋅ 3 H2O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g−1 at 100 mA g−1 after 150 cycles. The maximum capacity was reached 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. The final hybrid material is a promising material for lithium-ion battery (LIB) applications.

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). Here, 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.

Capacitive deionization with activated carbon (AC) electrodes has been widely applied for removing charged ions from aqueous solutions. Such carbon electrodes commonly contain a minor polymer binder and a minor carbon additive content. The choice of carbon additives is rarely investigated in depth regarding the performance enhancement/deterioration they might bring. In this work, we explored the influence of various carbon types, namely, onion-like carbon, carbon black, and micro-mesoporous carbons, on the desalination capacity and rate. Based on the cycling performance of 100 cycles, we draw relationships between the physicochemical properties of different carbon types and their results on electrochemical desalination performance. The results indicate that the direct use of the activated carbon electrode without additives leads to a higher desalination capacity of approximately 10 mg/g in early cycles, though at the cost of a lower desalination rate of 6 μg/g/s. The larger AC particles limit the intraparticle ion transportation due to the increased diffusion path length. The highest desalination rate (20 μg/g/s) is enabled by the incorporation of small and less porous additives, as it shortens the ion diffusion path length due to the increased size dispersion, hence improving the overall ion transport and desalination rates.

The widespread contamination of water resources with emerging organic contaminants necessitates the development of sustainable and cost-effective water treatment technologies. Adsorption, as a widely used water remediation process, is hampered by severe performance limitations against ionic and hydrophilic organic contaminants. In addition, no facile on-site regeneration techniques are available. Electrosorption of organic compounds (EOC) is a promising alternative to not only improve adsorption performance, but also to facilitate adsorbent regeneration by green electricity. The number of studies on EOC has grown exponentially over the past decades. There are numerous examples showing that applied electric potentials can significantly enhance the adsorption affinity, capacity, and kinetics of conductive carbon adsorbents. However, whether these effects are specific to certain compound classes or more generally applicable remains unclear as well as the optimal criteria for designing EOC processes. Therefore, we critically evaluated the current state of the art of EOC in terms of active control of adsorption and desorption processes and the achievable effects for ionic and neutral organic compounds. Through a detailed consideration of compound speciation and surface chemistry of electrode materials, we derive mechanistic insights into the EOC process and discuss differences between electrosorption of inorganic and organic compounds. We provide definitions and propose insightful performance parameters to unify the rapidly growing EOC research. Potential application scenarios and future research directions are discussed. Overall, EOC is less likely to be a one-fits-all solution for removing contaminants, but adds a valuable tool especially for the hydrophilic and ionic organic contaminants that challenge conventional adsorption processes.

Ionic liquid mixtures show promise as electrolytes for supercapacitors with nanoporous electrodes. Herein, we investigate theoretically and with experiments how binary electrolytes comprising a common anion and two types of differently-sized cations affect capacitive energy storage. We find that such electrolytes can enhance the capacitance of single nanopores and nanoporous electrodes under potential differences negative relative to the potential of zero charge. For a two-electrode cell, however, they are beneficial only at low and intermediate cell voltages, while a neat ionic liquid performs better at higher voltages. We reveal subtle effects of how the distribution of pores accessible to different types of ions correlates with charge storage and suggest approaches to increase capacitance and stored energy density with ionic liquid mixtures.

Electrochemical desalination shows promise for ion-selective, energy-efficient water desalination. This work reviews performance metrics commonly used for electrochemical desalination. We provide a step-by-step guide on acquiring, processing, and calculating raw desalination data, emphasizing informative and reliable figures of merit. A typical experiment uses calibrated conductivity probes to relate measured conductivity to concentration. Using a standard electrochemical desalination cell with activated carbon electrodes, we demonstrate the calculation of desalination capacity, charge efficiency, energy consumption, and ion selectivity metrics. We address potential pitfalls in performance metric calculations, including leakage current (charge) considerations and aging of conductivity probes, which can lead to inaccurate results. The relationships between pH, temperature, and conductivity are explored, highlighting their influence on final concentrations. Finally, we provide a checklist for calculating performance metrics and planning electrochemical desalination tests to ensure accuracy and reliability. Additionally, we offer simplified spreadsheet tools to aid data processing, system design, estimations, and upscaling.

Electrochemically converting nitrate, widely distributed in industrial wastewater and contaminated water bodies, into ammonia is a promising route for resource recovery and wastewater treatment. Meanwhile, treating harmful algal blooms (HABs) is presented worldwide, are time and resource-consuming, and carries a high CO2 footprint. Rather than considering this carbon and nitrogen-rich biomass as disposable waste, consider it a vast renewable resource. Therefore, this study presents a Fe-dispersed carbon-based catalyst derived from HABs biomass, with a maximum ammonia yield rate of 16449 μg h−1 cm−2 (1.2 mmol h−1 mgcat−1) and NH3 Faradaic efficiency of 87.3%. This catalyst also possessed decent stability with continuous operation over 50 h. Experimental and theoretical calculation results reveal that the Fe-N4 site facilitates electrocatalytic nitrate reduction reaction by reducing the energy barriers of the NO3–to-NH3 pathway. Thus, this strategy of upcycling HABs biomass waste into functional catalysts offers a multipronged approach to renewable and carbon-neutral energy technologies.

Sodium ion insertion plays a critical role in developing robust sodium-ion technologies (batteries and hybrid supercapacitors). Diffusion coefficient values of sodium (DNa+) in tin phosphide between 0.1 V and 2.0 V vs. Na/Na+ are systematically determined by galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). These values range between 4.55 × 10−12 cm2 s−1 and 1.94 × 10−8 cm2 s−1 and depend on the insertion/de-insertion current and the thickness of the electrode materials. Additionally, DNa+ values differ between the first and second cation insertion because of the solid electrolyte interface (SEI) formation. DNa+ vs. insertion potential alters non-linearly in a “W” form due to the strong interactions of Na+ with tin phosphide particles. The results reveal that GITT is a more appropriate electrochemical technique than PITT and EIS for evaluating DNa+ in tin phosphide.