Abstract:Interfacial
charging and ionic conductivity in the diffuse layer
of polycrystalline platinum (poly-Pt)– nonadsorbing electrolyte
interface were studied using a combined electrochemical–electrokinetic
method. Assuming no specific adsorption of ions, the electronic charge
on the metal (metal charge) was found to increase monotonically for
acidic, neutral, and basic pH, with the applied potential up to 0.95
V versus SHE. Nonmonotonic metal charging was not observed; however,
the metal charge was found to saturate… Show more
“…19,20 The latter is often called surface conduction of ions where the term "surface" refers to the local catalyst particlewater interface. This phenomenon has been studied from fundamental electric double layer perspective [21][22][23] as well as in porous electrodes. [24][25][26] From the impedance measurements at low and high relative humidity (RH) of the cathode gas feed, we calculate-1) the ionomer coverage, and 2) H + conductivity inside the electrode.…”
Section: Methodology and Cell Configurationsmentioning
Electrochemical CO2 reduction is a promising technology to capture and convert CO2 to valuable chemicals. High Faradaic efficiencies of CO2 reduction products are achieved with zero-gap alkaline CO2 electrolyzers with a supporting electrolyte at the anode (anolyte). Herein, we investigate the effect of the anolyte on the electrode properties such as catalyst utilization, ionic accessibility etc. of a CO2 reduction cathode using electrochemical techniques and cell configurations that avoid the complexities related to co-electrolysis. Using 1 M KOH as the anolyte and a Cu gas-diffusion-electrode with low Nafion content as the model CO2 reduction electrode, we find that electrode capacitance (proxy for electrochemically active surface area) and ionic conductivity inside the cathode increase approximately 4 and 447 times, respectively, in the presence of KOH. Liquid anolyte wets the electrode’s pore structure more efficiently than capillary condensation of the feed water vapor. The ionomer coverage is very low, and its distribution inside the electrode is highly fragmented. Surface ion conduction mechanisms inside the electrode are orders of magnitude lower than the bulk ion conduction in presence of anolyte. This study shows that when an anolyte (e.g., KOH) is used, catalyst utilization and ionic accessibility inside the electrode increase significantly.
“…19,20 The latter is often called surface conduction of ions where the term "surface" refers to the local catalyst particlewater interface. This phenomenon has been studied from fundamental electric double layer perspective [21][22][23] as well as in porous electrodes. [24][25][26] From the impedance measurements at low and high relative humidity (RH) of the cathode gas feed, we calculate-1) the ionomer coverage, and 2) H + conductivity inside the electrode.…”
Section: Methodology and Cell Configurationsmentioning
Electrochemical CO2 reduction is a promising technology to capture and convert CO2 to valuable chemicals. High Faradaic efficiencies of CO2 reduction products are achieved with zero-gap alkaline CO2 electrolyzers with a supporting electrolyte at the anode (anolyte). Herein, we investigate the effect of the anolyte on the electrode properties such as catalyst utilization, ionic accessibility etc. of a CO2 reduction cathode using electrochemical techniques and cell configurations that avoid the complexities related to co-electrolysis. Using 1 M KOH as the anolyte and a Cu gas-diffusion-electrode with low Nafion content as the model CO2 reduction electrode, we find that electrode capacitance (proxy for electrochemically active surface area) and ionic conductivity inside the cathode increase approximately 4 and 447 times, respectively, in the presence of KOH. Liquid anolyte wets the electrode’s pore structure more efficiently than capillary condensation of the feed water vapor. The ionomer coverage is very low, and its distribution inside the electrode is highly fragmented. Surface ion conduction mechanisms inside the electrode are orders of magnitude lower than the bulk ion conduction in presence of anolyte. This study shows that when an anolyte (e.g., KOH) is used, catalyst utilization and ionic accessibility inside the electrode increase significantly.
“…At potentials above 0.23 V, Pt is positively charged and will expel protons from the micropores and mesopores if in contact with water because double layers are thick. However, when Pt is in contact with ILs, the ionic strength of ILs is high and therefore the double layers will be thin, thus; electric field will be shielded within <0.5 nm from the surface of Pt and protons will not be impacted by positively charged Pt 24 – 26 . Fig.…”
Section: Introductionmentioning
confidence: 99%
“…At potentials above 0.23 V, Pt is positively charged and will expel protons from the micropores and mesopores if in contact with water because double layers are thick. However, when Pt is in contact with ILs, the ionic strength of ILs is high and therefore the double layers will be thin, thus; electric field will be shielded within <0.5 nm from the surface of Pt and protons will not be impacted by positively charged Pt [24][25][26] . Various research groups have incorporated IL small molecules or IL-containing ionomers into the cathode catalyst layers and showed improved catalytic activity toward ORR 8,9,27,28 , which was most often attributed solely to higher oxygen solubility and suppressed adsorption of non-reactive oxygenated species.…”
Ionic liquids (ILs) have shown to be promising additives to the catalyst layer to enhance oxygen reduction reaction in polymer electrolyte fuel cells. However, fundamental understanding of their role in complex catalyst layers in practically relevant membrane electrode assembly environment is needed for rational design of highly durable and active platinum-based catalysts. Here we explore three imidazolium-derived ionic liquids, selected for their high proton conductivity and oxygen solubility, and incorporate them into high surface area carbon black support. Further, we establish a correlation between the physical properties and electrochemical performance of the ionic liquid-modified catalysts by providing direct evidence of ionic liquids role in altering hydrophilic/hydrophobic interactions within the catalyst layer interface. The resulting catalyst with optimized interface design achieved a high mass activity of 347 A g−1Pt at 0.9 V under H2/O2, power density of 0.909 W cm−2 under H2/air and 1.5 bar, and had only 0.11 V potential decrease at 0.8 A cm−2 after 30 k accelerated stress test cycles. This performance stems from substantial enhancement in Pt utilization, which is buried inside the mesopores and is now accessible due to ILs addition.
“…The invisible nature of the EDL makes its behavior challenging to probe and to understand. Existing methods to characterize the dynamics of ions at the EDL, such as electrochemical impedance spectroscopy (EIS), infrared (IR) and Raman spectroscopy, force-related techniques, − X-ray spectroscopic methods, and electrokinetic streaming potentials, − result in numerical data that are generally challenging to interpret. This creates an impediment to the intuitive understanding of interfacial properties.…”
Electrochemical double layers (EDLs) govern the operation of batteries, fuel cells, electrochemical sensors, and electrolyzers. However, their invisible nature makes their properties and function difficult to conceptualize, creating an impediment to the broader understanding of double-layer function required for future technologies in energy storage and chemical synthesis. To render the behavior of electrochemical interfaces more intuitive, we made the rearrangement of interfacial components audible by employing the EDL as a variable element in a relaxation oscillator circuit. Connecting the circuit to a speaker generated an audible output corresponding to the change in potential resulting from EDL rearrangement. Variations in the applied voltage, electrolyte concentration and identity, as well as in the electrode material, yielded audible frequency variations that provide an intuitive understanding of EDL behavior. We expect that hearing the trends in behavior will provide a helpful and alternative method for understanding molecular movement at the electrochemical interface.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
