With the development of better catalysts, mass transport limitations are becoming a challenge to high throughput electrochemical reduction of CO 2 to CO. In contrast to optimization of electrodes for fuel cells, optimization of gas diffusion electrodes (GDE)consisting of a carbon fiber substrate (CFS), a micro porous layer (MPL), and a catalyst layer (CL)for CO 2 reduction has not received a lot of attention. Here, we studied the effect of the MPL and CFS composition on cathode performance in electroreduction of CO 2 to CO. In a flow reactor, optimized GDEs exhibited a higher partial current density for CO production than Sigracet 35BC, a commercially available GDE. By performing electrochemical impedance spectroscopy in a CO 2 flow reactor we determined that a loading of 20 wt% PTFE in the MPL resulted in the best performance. We also investigated the influence of the thickness and wet proof level of CFS with two different feeds, 100% CO 2 and the mixture of 50% CO 2 and N 2 , determining that thinner and lower wet proofing of the CFS yields better cathode performance than when using a thicker and higher wet proof level of CFS.
The effect of thickness in multilayer thin-film composite membranes on gas permeation has received little attention to date, and the gas permeances of the organic polymer membranes are believed to increase by membrane thinning. Moreover, the performance of defect-free layers with known gas permeability can be effectively described using the classical resistance in series models to predict both permeance and selectivity of the composite membrane. In this work, we have investigated the Pebax®-MH1657/PDMS double layer membrane as a selective/gutter layer combination that has the potential to achieve sufficient CO2/N2 selectivity and permeance for efficient CO2 and N2 separation. CO2 and N2 transport through membranes with different thicknesses of two layers has been investigated both experimentally and with the utilization of resistance in series models. Model prediction for permeance/selectivity corresponded perfectly with experimental data for the thicker membranes. Surprisingly, a significant decrease from model predictions was observed when the thickness of the polydimethylsiloxane (PDMS) (gutter layer) became relatively small (below 2 µm thickness). Material properties changed at low thicknesses—surface treatments and influence of porous support are discussed as possible reasons for observed deviations.
A free-standing
(biomacomolecule/synthetic inorganic nanotubes)
hybrid film was fabricated through an alternative layer-by-layer (LBL)
assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide
extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found
in volcano ash. The hybrid film thickness increased linearly with
the number of the bilayers, because of the interaction between the
negatively charged surface of sacran and the positively charged surface
of imogolite. UV–vis spectroscopy indicated that the LBL film
exhibited good transparency. The surface morphology of the LBL film
was smooth in the micrometer scale; many imogolite nanotubes were
adsorbed onto the sacran layer, while no imogolite clusters were observed.
Furthermore, the structure, stability, gas permeability, and mechanical
properties of the LBL films were investigated.
Robust,
nanometer-thick, permselective membranes were developed
by composite formation from poly(dimethylsiloxane) (PDMS) and cellulose
nanofibers (CNF). Their unique behavior is discussed in relation to
that of a single-component PDMS nanomembrane. In the absence of the
CNF component, the PDMS nanomembrane with a thickness of 34 nm displays
ultrahigh permeability of CO2 gas, which is only ca. one
order of magnitude smaller than that of free-flowing gases through
a porous poly(acrylonitrile) support film (PAN, thickness 150 μm).
The constant CO2/N2 selectivity observed for
the whole range of membrane thickness (34 nm–10 μm) suggests
that in the single-component membrane, the kinetic process at the
membrane surface determines the permselective behavior. Multilayered
composite membranes are obtainable by repeated spin coating. The mechanical
weakness of the single-component PDMS membrane is improved by complexation
with CNF, as confirmed by the bulge test and the ease of macroscopic
handling. Such a robust PDMS–CNF nanomembrane gives superior
permeation of 50,000 GPU with a defect-free PDMS layer of ca. 17 nm
thickness. Interestingly, the permeation characteristics of the composite
membrane are strongly affected by the asymmetric arrangement of PDMS
and CNF layers, and the gas permeation from the side of the CNF layer
is drastically reduced. The PDMS composite membrane is expected to
provide practically useful systems as a means of direct air capture.
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