Aqueous-phase electrochemical reduction of carbon dioxide requires an active, earth-abundant electrocatalyst, as well as highly efficient mass transport. Here we report the design of a porous hollow fibre copper electrode with a compact three-dimensional geometry, which provides a large area, three-phase boundary for gas–liquid reactions. The performance of the copper electrode is significantly enhanced; at overpotentials between 200 and 400 mV, faradaic efficiencies for carbon dioxide reduction up to 85% are obtained. Moreover, the carbon monoxide formation rate is at least one order of magnitude larger when compared with state-of-the-art nanocrystalline copper electrodes. Copper hollow fibre electrodes can be prepared via a facile method that is compatible with existing large-scale production processes. The results of this study may inspire the development of new types of microtubular electrodes for electrochemical processes in which at least one gas-phase reactant is involved, such as in fuel cell technology.

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a b s t r a c tSilicon carbide (SiC) membranes have shown large potential for applications in water treatment. Being able to make these membranes in a hollow fiber geometry allows for higher surface-to-volume ratios. In this study, we present a thermal treatment procedure that is tuned to produce porous silicon carbide hollow fiber membranes with sufficient mechanical strength. Thermal treatments up to 1500 1C in either nitrogen or argon resulted in relatively strong fibers, that were still contaminated with residual carbon from the polymer binder. After treatment at a higher temperature of 1790 1C, the mechanical strength had decreased as a result of carbon removal, but after treatments at even higher temperature of 2075 1C the SiC-particles sinter together, resulting in fibers with mechanical strengths of 30-40 MPa and exceptionally high water permeabilities of 50,000 L m À 2 h À 1 bar À 1 . Combined with the unique chemical and thermal resistance of silicon carbide, these properties make the fibers suitable microfiltration membranes or as a membrane support for application under demanding conditions.

Membrane separation under harsh conditions, such as high-p,T or in the presence of aggressive chemicals, requires a robust membrane support. In academia commonly ceramic disks are used for this purpose, but these disks posses a too low surface-area-to-volume ratio for practical applications. Ceramic hollow fibers potentially provide a much larger specific surface area, but applying a defect free thin selective layer on such structures is more intricate. Here we show the successful preparation of a thin polyamide layer on a thin porous hollow α-alumina fiber by interfacial polymerization of piperazine with trimesoyl chloride. Two aspects of the fabrication method are identified as particularly crucial for obtaining a high quality selective layer: i) the layer the ceramic surface should have a sufficient amount of hydroxyl groups for covalent attachment in order to avoid delamination, and ii) controlled drying steps are necessary to avoid local surplus or lack of liquid on the outer surface of the ceramic. To increase the hydroxyl group concentration, and to facilitate the presence of sufficient reactants in a large volume of small pores, the fibers have been coated with a layer of γ-alumina. Sufficiently long drying steps (20 mm) have been employed to avoid uneven drying over the length of the fiber. The obtained fibers show clean water fluxes in the range of 2-5 L m −2 h −1 bar −1 combined with a retention of Rose Bengal above 99%.

A route for the fabrication of porous inorganic hollow fibers with high surface‐area‐to‐volume ratio that avoids harmful solvents is presented. The approach is based on bio‐ionic gelation of an aqueous mixture of inorganic particles and sodium alginate during wet spinning. In a subsequent thermal treatment, the bio‐organic material is removed and the inorganic particles are sintered. The method is applicable to the fabrication of various inorganic fibers, including metals and ceramics. The route completely avoids the use of organic solvents, such as N‐methyl‐2‐pyrrolidone, and additives associated with the currently used fiber fabrication methods. In addition, it inherently avoids the manifestation of so‐called macro voids and allows the facile incorporation of additional metal oxides in the inorganic hollow fibers.

This paper presents a method for the fabrication of inorganic porous hollow fibers, using ecologically benign feed materials instead of organic solvents and harmful additives. Our method is based on ionic cross-linking of an aqueous mixture of sodium alginate, inorganic particles, and a carbonate. The mixture is spun into an acidic coagulation bath, where the low pH triggers the dissociation of the carbonate into multivalent cations and carbon dioxide. The multivalent cations cross-link the alginate, thereby consolidating the 3D structure and arresting the inorganic particles. In a subsequent thermal treatment the polymer is removed and the particles are sintered together. Adequate gelation requires a sufficiently low pH of the acid bath and a sufficing buffering capacity of the acid. In addition, to facilitate thermal treatment, it appears to be crucial that the acid has a conjugated base with limited propensity for complexing cations. The environmentally-safe and sustainable lactic acid and acetic acid are shown to be convenient acids. The fibers prepared via our method have outstanding properties, such as high mechanical strength, homogeneous morphology, and sharp distribution of small pores. In addition, they are prepared using sustainable chemicals such as lactic acid and calcium carbonate.

Porous hollow fibers are used for the first time as both support and metal source for electroforming of MOF films.