David Rehnlund

Flocculation is a physicochemical process with critical relevance to industrial and environmental operations, including potable water production, wastewater remediation, mineral processing, papermaking, and food manufacturing. The efficiency of flocculation is determined by the chemical nature, molecular structure, and physicochemical interactions of flocculants with suspended colloidal matter. Conventional synthetic polyacrylamides, available in nonionic, anionic, and cationic forms, function predominantly via electrostatic neutralization, polymer chain bridging, and sweep flocculation induced by precipitated hydroxides. Their high molecular weight, customizable charge density, and cost-effectiveness have consolidated their industrial dominance. However, the inherent resistance of polyacrylamides to biodegradation in combination with its monomer’s toxicity and increasing regulatory pressure have accelerated research toward sustainable alternative materials. Recent developments include functionalized natural polysaccharides (e.g., chitosan, cellulose derivatives, starch esters), bio-based copolymers, and nanoengineered hybrid systems incorporating inorganic domains to enhance colloid destabilization and sedimentation kinetics. This review systematically examines the physicochemical principles underlying flocculation, evaluates the performance parameters and limitations of polyacrylamides, and highlight emerging strategies for sustainable flocculant design. Prospects for the next generation of flocculation technologies are discussed in the context of mechanistic optimization, ecological safety, and compliance with evolving environmental regulations.

Alkali metal–sulfur batteries (particularly, lithium/sodium‐ sulfur (Li/Na–S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na–S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the “shuttle effect” caused by the high solubility of Li/Na–polysulfides. Herein, novel organosulfur‐containing materials, i.e., bis (4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS‐OH) and 2,4‐thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS‐OH shows an initial discharge/charge capacity of 353/192 mAh g ⁻¹ and a capacity of 62 mAh g ⁻¹ after 200 cycles at 100 mA g ⁻¹ in ether‐based Li‐ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248 mAh g ⁻¹ and better cycling performance (106 mAh g ⁻¹ after 200 cycles) than BiTEMPS‐OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li‐ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X‐ray powder diffraction reveals that BiTEMPS‐OH loses its crystalline structure permanently upon cycling in Li battery cells. X‐ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S−S bonds in BiTEMPS‐OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC.

Sustainable development can be pursued through electrification in all sectors, and energy storage devices -mainly batteries- play a crucial role in this process. This leads to an ever-increasing demand for rechargeable batteries. However, the current generation of the rechargeable batteries, namely lithium-ion batteries, is produced using elements such as Li, Ni, and Co which have limited resources. Sodium-ion batteries (SIBs) on the other hand are considered as a good alternative due to the abundance of Na resources and fundamental similarities of Na and Li. While the cathode material for SIBs has reached a commercial level of reliability, the identification of a high energy anode material still remains a challenge. Although Na metal as an anode material offers high energy density, the main issue is that Na metal has a tendency for dendritic growth during electrodeposition. In this work, different electrochemical strategies are used to mitigate dendritic Na growth. High overpotential nucleation pulses during stripping and/or plating steps are applied in order to induce two-dimensional growth. The impact of these strategies is studied using three-electrode symmetrical cells with Na metal as the working, counter, and reference electrodes, in an electrolyte composed of NaPF₆ in EC/PC with FEC as an additive. Chronopotentiograms recorded during extended cycling (with and without Na pre-nucleation) are examined with special attention being paid to the overpotentials occurring on each cycle. Ex-situ SEM images are used to relate the different potential profiles during extended galvanostatic cycling to the different surface morphologies. The results show that a combination of oxidative (stripping) and reductive (plating) pulses has an obvious effect on inhibiting dendritic growth during electrodeposition of Na metal. The results encourage the deployment of electrochemical strategies to prevent dendritic growth in Na metal anodes and paves the way for experiments with new electrolyte compositions to further help overcoming the challenges associated with Na deposition.

Rechargeable lithium‐based batteries generally exhibit gradual capacity losses resulting in decreasing energy and power densities. For negative electrode materials, the capacity losses are largely attributed to the formation of a solid electrolyte interphase layer and volume expansion effects. For positive electrode materials, the capacity losses are, instead, mainly ascribed to structural changes and metal ion dissolution. This review focuses on another, so far largely unrecognized, type of capacity loss stemming from diffusion of lithium atoms or ions as a result of concentration gradients present in the electrode. An incomplete delithiation step is then seen for a negative electrode material while an incomplete lithiation step is obtained for a positive electrode material. Evidence for diffusion‐controlled capacity losses is presented based on published experimental data and results obtained in recent studies focusing on this trapping effect. The implications of the diffusion‐controlled Li‐trapping induced capacity losses, which are discussed using a straightforward diffusion‐based model, are compared with those of other phenomena expected to give capacity losses. Approaches that can be used to identify and circumvent the diffusion‐controlled Li‐trapping problem (e.g., regeneration of cycled batteries) are discussed, in addition to remaining challenges and proposed future research directions within this important research area.

Rechargeable lithium batteries are well-known to exhibit progressive capacity decays upon cycling, leading to loss of cell voltage, power and energy. However, the origins of capacity losses are still not fully understood and are largely attributed to the formation of a solid electrolyte interface layer and volume expansion. Another largely overlook capacity decay mechanism is lithium trapping ^1–4. Lithium trapping, caused by incomplete delithiation, is here demonstrated to be the main source of capacity losses in high energy density anodes (e.g. Si) while SEI formation and dissolution affect the accumulated capacity loss due to decreased coulombic efficiency. In the following paper we will present our findings on capacity losses in standard and optimized Si-Li half cells and how these systems affect lithium trapping inside the active electrode material. We will discuss how the cycling protocol (e.g. full capacity cycling vs coulombic limited cycling) can mask signs of Li trapping and temporarily delay capacity decay in half-cells. We will highlight the importance of lithium-trapping induced capacity or voltage decays effect in lithium-based batteries, explain the mechanism for lithium-trapping and establish diffusion-controlled lithium-trapping models. Approaches toward identifying and circumventing lithium-trapping problem will also be discussed as well as challenges and proposed future research directions within this exciting and important research field. Figure 1. Capacity evolution for an optimized nano-Silicon composite electrode in a half-cell configuration during coulombic limited cycling (i.e. 1200 mAh/g). Critical capacity decay is observed when the accumulated trapped lithium has saturated the electrode core and counteracts the deposited Li layer ¹. References 1. Lindgren, F. et al. On the Capacity Losses Seen for Optimized Nano‐Si Composite Electrodes in Li‐Metal Half‐Cells. Adv. Energy Mater. 9, 1901608 (2019). 2. Rehnlund, D. et al. Lithium trapping in alloy forming electrodes and current collectors for lithium based batteries. Energy Environ. Sci. 10, 1350–1357 (2017). 3. Rehnlund, D., Pettersson, J., Edström, K. & Nyholm, L. Lithium Trapping in Microbatteries Based on Lithium- and Cu₂O-Coated Copper Nanorods. ChemistrySelect 3, 2311–2314 (2018). 4. Zhu, B. et al. Minimized lithium trapping by isovalent isomorphism for high initial Coulombic efficiency of silicon anodes. Sci. Adv. 5, eaax0651 (2019). Figure 1

Microbial cultivation with the aid of microfluidic flow chambers has a great potential to form biofilms on an easy to handle laboratory scale. Our microfluidic cultivation platform with a modular design offers versatility and precision in terms of simulating different environments to study multiple growth conditions¹. Thus, a long-term cultivation of biofilms can easily be obtained with the possibility of integrated on-line optical analysis. In this paper we will present our recent development of a bioelectrochemical microfluidic platform that allows cultivation and characterization of exoelectrogenic biofilms under anoxic conditions. Electroactive biofilms will be cultivated and characterized in the microfluidic bioelectrochemical system focusing on electroactive microorganisms such as Shewanella oneidensis. The conductive intracellular protein chain of these microbes enables extracellular electron transfer (EET) from the cytoplasm through the cell membranes to an insoluble electron acceptor, such as an anode ². Different deletion strains were cultivated and could be examined and compared with each other by chronoamperometry, electrochemical impedance spectroscopy, cyclic voltammetry and confocal laser scanning microscopy (CLSM). Genetically engineered strains focus on probing key genes that affect the biofilm forming properties of Shewanella oneidensis ³. In-situ fluorescence microscopy studies of biofilm formation and interaction will also be presented based on our modular microfluidic bioelectrochemical platform. We will also present our ongoing research on artificial electroactive biofilms that integrate electrodeposited nanostructures with a biocompatible hydrogel to form an artificial biofilm matrix. In summary, electroactive biofilm growth under anoxic conditions using an anode as electron sink can be studied using our microfluidic flow technology. Examples of the versatility of the system as well as future outlooks on further biofilm growth conditions will be presented. References 1. Hansen, S. H. et al. Machine-assisted cultivation and analysis of biofilms. Sci. Rep. 9, 8933 (2019). 2. Richter, K., Schicklberger, M. & Gescher, J. Dissimilatory Reduction of Extracellular Electron Acceptors in Anaerobic Respiration. Appl. Environ. Microbiol. 913–921 (2012). doi:10.1128/AEM.06803-11 3. Arinda, T. et al. Addition of Riboflavin-Coupled Magnetic Beads Increases Current Production in Bioelectrochemical Systems via the Increased Formation of Anode-Biofilms. Front. Microbiol. 10, 1–8 (2019).

The use of living microorganisms integrated within electrochemical devices is an expanding field of research, with applications in microbial fuel cells, microbial biosensors or bioreactors. We describe the use of porous nanocomposite materials prepared by DNA polymerization of carbon nanotubes (CNTs) and silica nanoparticles (SiNPs) for the construction of a programmable biohybrid system containing the exoelectrogenic bacterium Shewanella oneidensis. We initially demonstrate the electrical conductivity of the CNT-containing DNA composite by employment of chronopotentiometry, electrochemical impedance spectroscopy, and cyclic voltammetry. Cultivation of Shewanella oneidensis in the conductive materials shows that the exoelectrogenic bacteria populate the matrix of the conductive composite, while nonexoelectrogenic Escherichia coli remain on its surface. Moreover, the ability to use extracellular electron transfer pathways is positively correlated with the number of cells within the conductive synthetic biofilm matrix. The Shewanella-containing composite remains stable for several days and shows electrochemical activity, indicating that the conductive backbone is capable of extracting the metabolic electrons produced by the bacteria under strictly anoxic conditions and conducting them to the anode. Programmability of this biohybrid material system is demonstrated by on-demand release and degradation induced by a short-term enzymatic stimulus. We believe that the application possibilities of such biohybrid materials could even go beyond microbial biosensors, bioreactors, and fuel cell systems.

While the use of silicon‐based electrodes can increase the capacity of Li‐ion batteries considerably, their application is associated with significant capacity losses. In this work, the influences of solid electrolyte interphase (SEI) formation, volume expansion, and lithium trapping are evaluated for two different electrochemical cycling schemes using lithium‐metal half‐cells containing silicon nanoparticle–based composite electrodes. Lithium trapping, caused by incomplete delithiation, is demonstrated to be the main reason for the capacity loss while SEI formation and dissolution affect the accumulated capacity loss due to a decreased coulombic efficiency. The capacity losses can be explained by the increasing lithium concentration in the electrode causing a decreasing lithiation potential and the lithiation cut‐off limit being reached faster. A lithium‐to‐silicon atomic ratio of 3.28 is found for a silicon electrode after 650 cycles using 1200 mAhg⁻¹ capacity limited cycling. The results further show that the lithiation step is the capacity‐limiting step and that the capacity losses can be minimized by increasing the efficiency of the delithiation step via the inclusion of constant voltage delithiation steps. Lithium trapping due to incomplete delithiation consequently constitutes a very important capacity loss phenomenon for silicon composite electrodes.