Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%-97% have been produced for a number of well-established and emerging applications, such as molten metal filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.

Pump up the volume: Wet foams prepared with surfactants are thermodynamically unstable systems that undergo rapid disproportionation, drainage, and coalescence. Ultrastable foams have now been prepared using colloidal particles as stabilizers (left picture). The stabilization results from the irreversible adsorption at the air–water interface of particles surface‐modified with short‐chain amphiphiles (right picture).

Aqueous zinc batteries are highly attractive for large-scale storage applications owing to their inherent safety, low-cost, and durability. Yet, their advancement is hindered by a dearth of positive host materials (cathode) due to sluggish diffusion of Zn 2+ inside solid inorganic frameworks. Here, we report a novel organic host, tetrachloro-1,4-benzoquinone (also called: p-Chloranil), which due to its inherently soft crystal structure can provide reversible and efficient Zn 2+ storage. It delivers a high capacity of ≥200 mAh g-1 with a very small voltage polarization of 50 mV in a flat plateau around 1.1 V, which equate to an attractive specific energy of > 200 Wh kg-1 at an unparalleled energy efficiency (~95%). As unraveled by density functional theory (DFT) calculations, the molecular columns in p-Chloranil undergo a twisted rotation to accommodate Zn 2+ , thus restricting the volume change (-2.7%) during cycling. In-depth characterizations using operando X-ray

Bulk hierarchical porous ceramics with unprecedented strength-to-weight ratio and tunable pore sizes across three different length scales are printed by direct ink writing. Such an extrusion-based process relies on the formulation of inks in the form of particle-stabilized emulsions and foams that are sufficiently stable to resist coalescence during printing.

Wet foams are used in many important technologies either as end or intermediate products. However, the thermodynamic instability of wet foams leads to undesired bubble coarsening over time. Foam stability can be drastically improved by using particles instead of surfactants as foam stabilizers, since particles tend to adsorb irreversibly at the air-water interface. Recently, we presented a novel method for the preparation of high-volume particle-stabilized foams which show neither bubble growth nor drainage over more than 4 days. The method is based on the in-situ hydrophobization of initially hydrophilic particles to enable their adsorption on the surface of air bubbles. In-situ hydrophobization is accomplished through the adsorption of short-chain amphiphiles on the particle surface. In this work, we illustrate how this novel method can be applied to particles with various surface chemistries. For that purpose, the functional group of the amphiphilic molecule was tailored according to the surface chemistry of the particles to be used as foam stabilizers. Short-chain carboxylic acids, alkyl gallates, and alkylamines were shown to be appropriate amphiphiles to in-situ hydrophobize the surface of different inorganic particles. Ultrastable wet foams of various chemical compositions were prepared using these amphiphiles. The simplicity and versatility of this approach is expected to aid the formulation of stable wet foams for a variety of applications in materials manufacturing, food, cosmetics, and oil recovery, among others.

Aqueous Zn-ion batteries, which are being proposed as large scale energy storage solutions due to their unparalleled safety and cost advantage, are comprised of a positive host (cathode) material, a metallic zinc anode, and a mildly acidic aqueous electrolyte (pH ~ 3 -7). Typically, the charge storage mechanism is believed to be reversible Zn 2+ (de)intercalation in the cathode host, with the exception of α-MnO2, for which multiple vastly different and contradicting mechanisms have been proposed. However, our present study, combining electrochemical, operando X-ray diffraction (XRD), electron microscopy in conjunction with energy dispersive X-ray spectroscopy (EDX), and in situ pH evolution analyses on two oxide hosts -tunneled α-MnO2 and layered V3O7•H2O vis-à-vis two non-oxide hostslayered VS2 and tunneled Zn3[Fe(CN)6]2, suggests that oxides and non-oxides follow two dissimilar charge storage mechanisms. While the oxides behave as dominant proton intercalation materials, the non-oxides undergo exclusive zinc intercalation.Stabilization of the H + on the hydroxyl terminated oxide surface is revealed to facilitate the proton 2 intercalation by a preliminary molecular dynamics simulation study. Proton intercalation for both oxides leads to the precipitation of layered double hydroxide (LDH) -Zn4SO4(OH)6•5H2O with ZnSO4/H2O electrolyte and a triflate anion (CF3SO3 -) based LDH with Zn(SO3CF3)2/H2O electrolyte -on the electrode surface. The LDH precipitation buffers the pH of the electrolytes to a mildly acidic value, sustaining the proton intercalation to deliver large specific capacities for the oxides. Moreover, we also show that the stability of the LDH precipitate is crucial for the rechargeability of the oxide cathodes, revealing a critical link between the charge storage mechanism and the performance of the oxide hosts in aqueous zinc batteries.

Aufgeblasen: Nasse Schäume, die mithilfe von Detergentien präpariert werden, sind thermodynamisch instabile Systeme, die schneller Disproportionierung, Entwässerung und Koaleszenz unterliegen. Nun gelang die Bereitung ultrastabiler Schäume mithilfe kolloidaler Partikel als Stabilisatoren (linkes Bild). Die Stabilisierung ist das Ergebnis der irreversiblen Adsorption von Partikeln, die mit kurzkettigen Amphiphilen modifiziert wurden, an der Luft‐Wasser‐Grenzfläche (rechtes Bild).

We present a novel direct-foaming method to produce macroporous ceramics using particles instead of surfactants as stabilizers of the wet foams. This method allows for the fabrication of ultra-stable wet foams that resist coarsening upon drying and sintering. Macroporous ceramics of various chemical compositions with open or closed cells, average cell sizes ranging from 10 to 300 lm and porosities within 45% and 95%, can be easily prepared using this new approach. The sintered foams show high compressive strengths of up to 16 MPa in alumina foams with porosities of 88%.