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I wouldn't mind this, though how would an Electrode propel itself across the water? I don't think trying to roll would accomplish anything, spinning wouldn't do any good, and anything involving electricity in the water is just begging for trouble. How would a pokemon with 4x weakness to water learn surf?
And the bears what was left were cloaked in acid washed denim, and stately stones of rhine. For example: Clefable, Wigglytuff, Kangaskhan "Mickey is a relic of another era. Dumb-Fumbler posted For example: Clefable, Wigglytuff, Kangaskhan None are weak to water No but you did User Info: Crudelitas.
Maybe with its tongue? I mean, how does Clamperl swim? There is no path to git gud, for gitin' gud is the path. More topics from this board BDSP patch datamines doesn't have post pokemon? Build 1 Answer. Ask A Question. In another study, 1—1. It is important to note that these catalysts were tested over a planar electrode in an H-cell, where CO 2 reaches the catalyst surface via the electrolyte bulk. The reaction at the electrode immersed in the electrolytes may be limited by both the availability of local CO 2 and active sites wetted catalyst surface , which can be alleviated in a GDE structure.
Therefore, the sweet point for GDEs operating at high current densities may shift towards a higher hydrophobicity to ensure sufficient gas transport in the CLs see Section 2. In one example, Xing et al. This work also demonstrated that the pore sizes could be manipulated by varying the size of the PTFE nanoparticles: small PTFE particles lead to the formation of small hydrophobic pores. According to the Young—Laplace equation discussed in Section 2.
The deconvolution of the impedance spectra against equivalent circuit models shows that increasing hydrophobicity significantly reduces the thickness of the diffusion layers from This is likely a consequence of the balanced gas transport and the availability of active sites in the GDE Fig. The importance of maintaining the hydrophobic pathways was confirmed by the observed degradation of formate selectivity with the addition of surfactant in the electrolyte, which makes the liquid phase easy to spread and wet the CL pores by reducing the liquid tensions Fig.
The states of the deposited ionomers, such as molecular conformations, distribution in the CLs, water uptake, and ion conductivity, are strongly influenced by the ionomer chemical parameters Fig. How these properties alter the states of deposited ionomers have been widely studied in the field of PEM fuel cells. Table 4 lists the detailed solubility parameters and the dielectric constants for the solvents and the PFSAs, as mainly reported by Ma et al.
In the solvents e. A high dielectric constant increases the strengths of the electrostatic repulsion between PFSA molecules, leading to a reduced degree of the backbone aggregations. The large size of the backbone and ionic aggregates normally lead to large pores in the CLs, a high water uptake, and fast proton conduction. Small aggregates are prone to form continuous networks but with small-size pores.
These hydrophilic aggregates likely point towards polar catalyst surfaces or carbon materials, leaving the hydrophobic backbones pointing outside to facilitate gas transport. In contrast, the solvents having a closer solubility parameter to the hydrophobic backbones could help ionomer to form intimate contact with the CL constituents, thus extending the electrochemical surface areas in the CLs. Increasing the drying temperature accelerates molecular motions and leads to the ordering or crystalline of the ionomers.
The locally ordered ionomer resists water swelling and thus has a lowered water content or increased hydrophobicity and ion conductivity.
However, fast evaporation of the solvents resists the movement of the deposited ionomers and thus benefit the formation of a homogeneous distribution of the ionomers in the CLs.
What also important is the method to fabricate the ionomer—catalyst layers on the GDLs. Lees et al. They reported that the automated ultrasonic spray coating technique generated a more uniform ionomer distribution across the CLs, as evidenced by a much lower spatial variance of ionomers 0. This result is consistent with the qualitative observations by the Kenis group. Modifying the catalyst surface with hydrophilic or hydrophobic organics can alter the CO 2 RR product distribution via modulation of local water availability and metal hydricity i.
They found that the hydrophilic organics tend to promote formate production and HER, while cationic hydrophobic modifiers enhance CO selectivity Fig. This general trend indicates that the bulk properties in addition to the molecular chemistry of the organic modifiers also play a role in determining the product distributions likely via influencing catalyst local environment.
The modeling results unveiled that the modifier with shorter hydrocarbon chains has a water density 1. This is consistent with what we discussed in Section 3. More importantly, the authors reported that the hydrophilic surface has a weaker metal—hydride bond than the hydrophobic surface. Therefore, the hydride having weak interaction with the metal surface can be easily added to CO 2 to produce formate Fig. In contrast, the CO evolution is not influenced significantly by the strength of the metal—hydride bond, as the protons needed for CO evolution are sourced from the surrounded water molecules instead of the metal hydride.
The restricted water access and increased local pH could both suppress hydrogen evolution, which was widely reported over hydrophobic surfaces, as obtained by either increasing the loading of the hydrophobic materials e. The high local pH, likely resulting from the limited water diffusion, is the main reason for the promoted C 2 H 4 and lowered HER.
If containing cations such as quaternary ammoniums, the modifier could also suppress the HER by limiting the proton availability within the electric double layers. All these phase properties and operating conditions play significant roles in maintaining an ideal capillary pressure to prevent unwanted electrolyte flooding. These properties are also key contributors to the interfacial electric field, catalytic activity, electron conductivity, and product distribution.
Trade-offs usually exist because of the general observations: i. These limitations cause challenges for designing a CO 2 RR electrode that is not only active and selective for CO 2 RR but also capable of maintaining efficient multiple flows within the electrode. Recent literature demonstrated exciting opportunities to finely tune the wettability of the electrode via manipulating the material composition, particle sizes, pore structures, surface chemistry, and structures at multiscale, particularly taking advantage of the advances in the fields such as PEM fuel cells, polymer science, and material engineering.
Decoupling the gas transport and current distribution functionalities of the gas-diffusion layers, replacing porous carbon matrix e. The polymer-based GDLs has also demonstrated their potential to precisely control their pore size and structures, which also determine the gas permeance and retention time and provide an alternative avenue to improve the CO 2 RR selectivity. The catalyst layers are where multiple phases interact and the reaction primarily occurs, so wettability needs to be controlled to ensure efficient transport and maximize electrochemical surface area at a macroscale and achieve optimal local environment at catalyst surface in a microscale.
Tailoring the hydrophobicity, particle sizes, and morphologies of the additives is effective in adjusting the CL wettability on a macroscale. Designing the chemical structure e. The micro wettability adjustment may also influence the catalyst surface chemistry and electronic structure, which are also important for CO 2 RR catalysis.
The stability of the catalyst—modifier interface also relies on the material properties and the conditions of the local environment but remains underexplored by far.
Based on the discussion of the electrode wettability in Sections 2 and 3, we believe the following future directions are worthy of being explored when pursuing the desired wetting conditions for the next generation of GDEs at commercially relevant current densities. Besides, the PZC values of the electrically conducting carbon materials in the MPL can be shifted towards a more negative value through surface modification, such as the incorporation of polymers with positively charged functional groups.
A more negative PZC weakens the actual interfacial electric field and thus resists electrowetting. A patterned electrode surface could be another strategy to weaken the local interfacial field and therefore reduce the degree of electrowetting by increasing the density of active sites.
This strategy has been widely used in PEM fuel cell developments, , and could be valid in the case of CO 2 RR as long as the transport of the multiphase flows are carefully managed. Additionally, if we reconsider the electrolyte flooding as a position shift of the gas—liquid interfaces from the liquid side to the gas side, the CL may not be necessarily only at the interface in between the GDL and electrolyte or membrane.
Alternatively, the catalyst can be embedded in the GDLs with a loading profile across the electrode. Therefore, the CO 2 starvation issue due to flooding might be alleviated.
DOI: A , , 9 , Received 30th April , Accepted 8th July Abstract The electrochemical reduction of carbon dioxide CO 2 RR requires access to ample gaseous CO 2 and liquid water to fuel reactions at high current densities for industrial-scale applications. PZC is short for the potential of zero charges. The electrode can be considered as interfaces of materials with varied wettability. The defect could be either chemical defects corners, kinks, dopant or vacancies or microstructure defects e.
Reproduced from ref. Adapted from ref. Metal-based materials. Most clean metal surfaces are intrinsically hydrophilic as a result of the London dispersion forces. Under non-ideal conditions, oxygen vacancies i. The extent of their impact on wettability depends upon the materials' defect chemistry. Sarkar et al. Therefore, the former strengthens the water—solid interactions and improves the water wettability.
The red color describes the electric field profiles. The insets are examples of the water droplets on the catalyst layer.
Carbon-based materials. Carbon materials such as carbon fibers, carbon black, and carbon nanotubes are generally more hydrophobic than metals. Carbon nanotubes and graphene are more hydrophobic than carbon black due to the lack of high-energy defects at the surface. The heterogenous atoms e. This effect has been widely exemplified by the enhanced hydrophilicity for carbon surfaces with a high oxygen coverage. Organic additives — binders and ionomers. Fluorinated polymers such as PTFE 74,76,, and fluorinated silane are the most commonly used materials to increase the hydrophobicity of GDLs and CLs because of their high hydrophobicity and chemical stability.
Its high hydrophobicity originates from the fluorine's low polarizability and low London dispersion force, and its high chemical stability arises from fluorine's high electronegativity that makes C—F bonds strong.
Polymers with long non-polar hydrocarbon chains, such as 1-octadecanethiol, are also hydrophobic. Carbon-based GDLs. As discussed in Section 2. A dense MPL is generally needed because the primary support structure contains larger pores usually in tens of micrometers in diameter , leading to lower capillary pressures. Instead, the microporous layer MPL is a non-structural, thin hydrophobic layer with nanosized pores located between the macroporous layer and the CL.
The MPL then acts as the primary conductive contact layer with the catalyst layer, the access point for gas diffusion, and the first barrier to electrolyte flooding. Finally, treated in an air plasma apparatus for 0. Finally, treated in an air plasma apparatus for 1. Finally, treated in an air plasma apparatus for 2. The collected solid products were washed well before dried in a vacuum. SCE The above catalyst ink was sprayed on the carbon paper GDL.
This coating ink was air-brushed onto one side of the oxidized Cu gauze for the formation of a gas diffusion layer. Non-carbon based GDLs. Unfortunately, most of the existing carbon-based GDLs are incapable of preventing electrolyte flooding completely due to electrowetting and the presence of carbons that easily lose their hydrophobicity, particularly in alkaline electrolyte environment. Reducing catalyst overpotential. As the main driver for electrowetting and electrode flooding, the interfacial electric field can be lowered to improve the electrode wetting stability.
This can be achieved by developing a catalyst with reduced onset potentials the potential at which the reaction starts and increased density of the active sites.
These trends suggest that the flooding is likely associated with the activation of the carbon surfaces, which was further confirmed by the loss of F and increased oxygen species at the bare GDL surface. We believe the reported onset potentials partially depend on the PZCs of the catalyst materials, as listed in Table 1. This means one could also manipulate the catalyst material and facets to shift the PZC of catalysts to a more cathodic position, which has not been fully explored in the current literature.
Morphological effects on contact angles. There have been tremendous advances in the catalyst development for CO 2 RR via optimizing the electronic structures, surface chemistry, microstructures, dimensions, particle sizes, and interparticle distances. This review will not cover detailed strategies to develop catalysts to improve kinetic overpotentials, and we recommend readers to refer to recent catalyst reviews. Addition of hydrophobic materials in the CLs. Hydrophobic particulates such as PTFE nanoparticles can be directly added to the CL to create a hydrophobic microenvironment around the catalysts.
The hydrophobic materials need to be pre-mixed with the catalyst materials before catalyst deposition to achieve a uniform dispersion in the CL. RHE for 2 hours. Addition of ionomers in the CLs. The ionomers such as perfluorinated sulfonic acid PFSA or commercially available as Nafion containing hydrophobic backbones can be used to create pathways for gas transport in the CLs.
The catalyst structure achieved a notable improvement of the current densities of the gas reduction reactions. Table 4 Summary of the solubility parameters and dielectric constants of solvents and Nafion ionomer , Addition of organic modifiers.
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