Facile Designed Manganese Oxide/Biochar for Efficient Salinity Gradient Energy Recovery in Concentration Flow Cells and Influences of Mono/Multivalent Ions

Reduced Lattice Constant in Al-Doped LiMn2O4 Nanoparticles for Boosted Electrochemical Lithium Extraction

Extracting lithium selectively and efficiently from brine sources is crucial for addressing energy and environmental challenges. The electrochemical system employing LiMn2O4 (LMO) electrodes has been recognized as an effective method for lithium recovery. However, the lithium selectivity and stability of LMO need further enhancement for its practical applications. Herein, the Al-doped LMO with reduced lattice constant is successfully fabricated through a facile one-step solid-state sintering method, leading to enhanced lithium selectivity. The reduced lattice constant in Al-doped LMO is proved through spectroscopic analyses and theoretic calculations. Compared to the original LMO, the Al-doped LMO (LiAl0.05Mn1.95O4, LMO-Al0.05) exhibits highercapacitance, lower resistance, and improved stability. Moreover, the LMO-Al0.05 with reduced lattice constant can offer higher Li+ diffusion coefficient and lower intercalation energy revealed by cyclic voltammetry and multiscale simulations. When employed in hybrid capacitive deionization (CDI), the LMO-Al0.05 obtains a Li+ intercalation capacity of 21.7 mg g-1 and low energy consumption of 2.6 Wh mol-1 Li+. Importantly, the LMO-Al0.05 achieves a high Li+ extraction percentage (≈86%) with Li+/Na+ and Li+/Mg2+ selectivity of 1653.8 and 434.9, respectively, in synthetic brine. The results demonstrate that the Al-doped LMO with reduced lattice constant could be a sustainable solution for electrochemical lithium extraction.

Unraveling Flow Effect on Capacitive Energy Extraction from Salinity Gradients

The harvesting of salinity gradient energy through a capacitive double-layer expansion (CDLE) technique is directly associated with ion adsorption and desorption in electrodes. Herein, we show that energy extraction can be modulated by regulating ion adsorption/desorption through water flow. The flow effects on the output energy, capacitance, and energy density under practical conditions are systematically investigated from a theoretical perspective, upon which the optimal operating condition is identified for energy extraction. We demonstrate that the net charge accumulation displays a negative correlation with the water flow velocity and so does the surface charge density, and this causes a nontrivial variation in the magnitude of output energy when water flows are introduced. When high water flows are introduced in both the charging and discharging processes, the energy extraction can be significantly reduced by 47.69-49.32%. However, when a high flow is solely exerted in the discharging process, the energy extraction can be enhanced by 12.94-14.49% even at low operation voltages. This study not only offers a comprehensive understanding of the microscopic mechanisms of surface-engineered energy extraction with water flows but also provides a novel direction for energy extraction enhancement.

Boosted brackish water desalination and water softening by facilely designed MnO2/hierarchical porous carbon as capacitive deionization electrode

Capacitive deionization (CDI) is a promising technique for brackish water desalination. However, its salt electrosorption capacity is insufficient for practical application yet, and little information is available on hardness ion (Mg²⁺, Ca²⁺) removal in CDI. Herein, hierarchical porous carbon (HPC) was prepared from low-cost and renewable microalgae via a simple one-pot approach, and both MnO₂/HPC and polyaniline/HPC (PANI/HPC) composites were then synthesized using a facile, one-step hydrothermal method. Compared with the MnO₂ electrode, the MnO₂/HPC electrode presented an improved hydrophilicity, higher specific capacitance, and lower electrode resistance. The electrodes exhibited pseudocapacitive behaviors, and the maximum salt electrosorption capacities of MnO₂/HPC-PANI/HPC CDI cell was up to 0.65 mmol g^-1 NaCl, 0.71 mmol g^-1 MgCl₂, and 0.76 mmol g^-1 CaCl₂, respectively, which were comparable and even higher than those of the previously reported CDI cells. Additionally, the MnO₂/HPC electrode presented a selectivity order of Ca²⁺ ≥ Mg²⁺ > Na⁺, and the divalent cation selectivity was found to be attributed to their stronger binding strength in the cavity of MnO_2. Multiscale simulations further reveal that the MnO₂/HPC electrodes with the unique luminal configuration of MnO₂ and HPC as supportive framework could offer a great intercalation selectivity of the divalent cations and exhibit a great promise in hardness ion removal.

Manganese oxide-modified biochar: production, characterization and applications for the removal of pollutants from aqueous environments - a review

The development of manganese (Mn) oxides (MnOx) modified biochar (MnOBC) for the removal of pollutants from water has received significant attention. However, a comprehensive review focusing on the use of MnOBC for the removal of organic and inorganic pollutants from water is missing. Therefore, the preparation and characterization of MnOBC, and its capacity for the removal of inorganic (e.g., toxic elements) and organic (e.g., antibiotics and dyes) from water have been discussed in relation to feedstock properties, pyrolysis temperature, modification ratio, and environmental conditions here. The removal mechanisms of pollutants by MnOBC and the fate of the sorbed pollutants onto MnOBC have been reviewed. The impregnation of biochar with MnOx improved its surface morphology, functional group modification, and elemental composition, and thus increased its sorption capacity. This review establishes a comprehensive understanding of synthesizing and using MnOBC as an effective biosorbent for remediation of contaminated aqueous environments.

Tandem Osmotic Engine Based on Hydrogel Particles with Antipolyelectrolyte and Polyelectrolyte Effect Fuelled by Both Salinity Gradient Modes

In this study, we propose a new approach to attain energy by salinity gradient engines with pistons based on hydrogels possessing polyelectrolyte and antipolyelectrolyte effects in a tandem arrangement, providing energy in each salinity gradient mode in a repeatable manner. The swelling of hydrogel with a polyelectrolyte effect and shrinking of hydrogel particles possessing an antipolyelectrolyte effect in desalinated water, and subsequent shrinking of hydrogel with polyelectrolyte and swelling of hydrogel antipolyelectrolyte effect in saline water, generate power in both increasing and decreasing salinity modes. To investigate the energy recovery, we scrutinized osmotic engine assemblies by a setup arrangement of pistons with hydrogel particles, with polyelectrolyte and antipolyelectrolyte effects, in tandem. The energy recovery from the tandem engine setup (calculated based on dry form for each polyelectrolyte polyacrylate-based hydrogel-SPA) and antipolyelectrolyte–sulfobetaine-based gel with methacrylate polymeric backbone-SBE) up to 581 J kg⁻¹ and a mean power of 0.16 W kg⁻¹ was obtained by the tandem setup of SPA and SBE hydrogel containing 3% crosslinking density and particle size of 500 microns with an external load of 3.0 kPa. Exchange of sulfobetaine with methacrylamide (SBAm), the main polymer backbone, revealed a positive increase in energy recovery of 670 J kg⁻¹ with a mean power of 0.19 W kg⁻¹ for the tandem system operating under the same parameters (SPA@SBAm). The energy recovery can be controlled, modulated and tuned by selecting both hydrogels with antipolyelectrolyte and polyelectrolyte effects and their performing parameters. This proof of concept provides blue energy harvesting by contributing both polyelectrolyte and antipolyelectrolyte effects in a single tandem setup; together with easy accessibility (diaper-based materials (SPA)) and known antibiofouling, these properties offer a robust alternative for energy harvesting.