A Combined Heat- and Power-Driven Membrane Capacitive Deionization System

Here, we experimentally investigate an alternative membrane capacitive deionization (MCDI) system cycle, which aims to reduce the required electrical energy demand for water treatment. The proposed heat and power combined MCDI system utilizes waste heat to control the electrostatic potential of the charged electrodes during the charging (desalination) and discharging (energy recovery) processes. The experimental findings suggest that with an increase in the temperature of the brine from 20 to 50 °C, the electrical energy consumed can be reduced by nearly 10%. We also show that the dependence of electrostatic potential on concentration may limit energy recovery performance (power), when moving toward higher water recoveries. Alternative desalination cycles can be further explored through evaluating non-isothermal and non-adiabatic system operation

Confinement Effects on Moisture-Swing Direct Air Capture

Direct air capture technologies are energy intensive and often utilize pressure and temperature swings for sorbent regeneration. An alternative approach, called moisture-swing direct air capture, relies on the hydrolysis of a confined anion to produce hydroxide anions. These hydroxide anions are active sites for CO2 capture. Here, we examine how confinement affects moisture-swing CO2 capture and regeneration mechanisms. The local short-range order in micropores determines the capacity for hydroxide formation in the moisture-controlled reversible hydrolysis/neutralization reaction during capture and regeneration. Carbon capture scales with the basicity of the confined anion. Sulfide exhibits excessive interactions with water and thus can release only small amounts of CO2 during the regeneration step. Control over local water–anion chemical microenvironments is critical for reversible operation of moisture-swing sorbent materials. Accessibility of water is largely governed by the distribution of resin macropores. Engineering materials for control over micro, meso, and macropores is critical for achieving favorable interactions between active sites and water in confinement

Using Flow Electrodes in Multiple Reactors in Series for Continuous Energy Generation from Capacitive Mixing

Efficient conversion of “mixing energy” to electricity through capacitive mixing (CapMix) has been limited by low energy recoveries, low power densities, and noncontinuous energy production resulting from intermittent charging and discharging cycles. We show here that a CapMix system based on a four-reactor process with flow electrodes can generate constant and continuous energy, providing a more flexible platform for harvesting mixing energy. The power densities were dependent on the flow-electrode carbon loading, with 5.8 ± 0.2 mW m^–2 continuously produced in the charging reactor and 3.3 ± 0.4 mW m^–2 produced in the discharging reactor (9.2 ± 0.6 mW m^–2 for the whole system) when the flow-electrode carbon loading was 15%. Additionally, when the flow-electrode electrolyte ion concentration increased from 10 to 20 g L^–1, the total power density of the whole system (charging and discharging) increased to 50.9 ± 2.5 mW m^–2

Effect of Pore Connectivity on Li Dendrite Propagation within LLZO Electrolytes Observed with Synchrotron X‑ray Tomography

Li₇La₃Zr₂O₁₂ (LLZO) is a garnet-type material that demonstrates promising characteristics for all-solid-state battery applications due to its high Li-ion conductivity and its compatibility with Li metal. The primary limitation of LLZO is the propensity for short-circuiting at low current densities. Microstructure features such as grain boundaries, pore character, and density all contribute to this shorting phenomenon. Toward the goal of understanding processing-structure relationships for practical design of solid electrolytes, the present study tracks structural transformations in solid electrolytes processed at three different temperatures (1050, 1100, and 1150 °C) using synchrotron X-ray tomography. A subvolume of 300 μm³ captures the heterogeneity of the solid electrolyte microstructure while minimizing the computational intensity associated with 3D reconstructions. While the porosity decreases with increasing temperature, the underlying connectivity of the pore region increases. Solid electrolytes with interconnected pores short circuit at lower critical current densities than samples with less connected pores

Charge- and Size-Selective Ion Sieving Through Ti₃C₂T_<i>x</i> MXene Membranes

Nanometer-thin sheets of 2D Ti₃C₂T_<i>x</i> (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m²) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 Å) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides

Composite Manganese Oxide Percolating Networks As a Suspension Electrode for an Asymmetric Flow Capacitor

In this study, we examine the use of a percolating network of metal oxide (MnO₂) as the active material in a suspension electrode as a way to increase the capacitance and energy density of an electrochemical flow capacitor. Amorphous manganese oxide was synthesized via a low-temperature hydrothermal approach and combined with carbon black to form composite flowable electrodes of different compositions. All suspension electrodes were tested in static configurations and consisted of an active solid material (MnO₂ or activated carbon) immersed in aqueous neutral electrolyte (1 M Na₂SO₄). Increasing concentrations of carbon black led to better rate performance but at the cost of capacitance and viscosity. Furthermore, it was shown that an expanded voltage window of 1.6 V could be achieved when combining a composite MnO₂-carbon black (cathode) and an activated carbon suspension (anode) in a charge balanced asymmetric device. The expansion of the voltage window led to a significant increase in the energy density to ∼11 Wh kg^–1 at a power density of ∼50 W kg^–1. These values are ∼3.5 times and ∼2 times better than a symmetric suspension electrode based on activated carbon