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At least 1,117 records · Page 62

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NASA NTRS1991

Controllable surface-plasmon resonance in engineered nanometer epitaxial silicide particles embedded in silicon

Epitaxial CoSi2 particles in a single-crystal silicon matrix are grown by molecular-beam epitaxy using a technique that allows nanometer control over particle size in three dimensions. These composite layers exhibit resonant absorption predicted by effective-medium theory. Selection of the height and diameter of disklike particles through a choice of growth conditions allows tailoring of the depolarization factor and hence of the surface-plasmon resonance energy. Resonant absorption from 0.49 to 1.04 eV (2.5 to 1.2 micron) is demonstrated and shown to agree well with values predicted by the Garnett (1904, 1906) theory using the bulk dielectric constants for CoSi2 and Si.

Fathauer, R. W.↗

NASA NTRS2018

Can Semi-Volatile Organic Aerosols Lead to Fewer Cloud Particles?

The impact of condensing organic aerosols on activated cloud number concentration is examined in a new aerosol microphysics box model, MATRIX-VBS. The model includes the volatility-basis set (VBS) framework coupled with the aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state) that resolves aerosol mass and number concentrations and aerosol mixing state. By including the condensation of organic aerosols, the new model produces less activated particles compared to the original model, which treats organic aerosols as non-volatile. Parameters such as aerosol chemical composition, mass and number concentrations, and particle sizes which affect activated cloud number concentration are thoroughly tested via a suite of Monte-Carlo simulations. Results show that by considering semi-volatile organics in MATRIX-VBS, there is lower activated particle number concentration, except in cases with low cloud updrafts, in clean environment at above freezing temperatures, and in polluted environments at high temperature (310K) and extremely low humidity conditions.

Gao, Chloe Y.↗

NASA NTRS1991

A collection of diverse micrometeorites recovered from 100 tonnes of Antarctic blue ice

A new type of meteoritic material, intermediate in size between meteorites and interplanetary dust particles (IDPs), is described. Melting and filtering of about 100 tons of blue ice near Cap Prudhomme, Antarctica, yielded 7500 or more irregular, friable particles and about 1500 melted spherules, about 100 microns in size, both showing a 'chondritic' composition suggestive of an extraterrestrial origin. Analyzed irregular particles appear to be unmelted and have similarities with the fine-grained matrix of primitive carbonaceous chondrites, but are extremely diverse in composition. Isotopic analysis of trapped neon confirms an extraterrestrial origin for 16 of 47 irregular particles and 2 of 19 spherules studied and strongly suggests that they were exposed in space as micrometeoroids. These large Antarctic micrometeorites constitute a new family, or at least a new population, of solar system objects, in a mass range corresponding to the bulk of extraterrestrial material accreted by the earth today.

Maurette, M.↗

NASA NTRS2003

Radiation Transport Properties of Potential In Situ-Developed Regolith-Epoxy Materials for Martian Habitats

Mission crews in space outside the Earth s magnetic field will be exposed to high energy heavy charged particles in the galactic cosmic radiation (GCR). These highly ionizing particles will be a source of radiation risk to crews on extended missions to the Moon and Mars, and the biological effects of and countermeasures to the GCR have to be investigated as part of the planning of exploration-class missions. While it is impractical to shield spacecraft and planetary habitats against the entire GCR spectrum, biological and physical studies indicate that relatively modest amounts of shielding are effective at reducing the radiation dose. However, nuclear fragmentation in the shielding materials produces highly penetrating secondary particles, which complicates the problem: in some cases, some shielding is worse than none at all. Therefore the radiation transport properties of potential shielding materials need to be carefully investigated. One intriguing option for a Mars mission is the use of material from the Martian surface, in combination with chemicals carried from Earth and/or fabricated from elements found in the Martian atmosphere, to construct crew habitats. We have measured the transmission properties of epoxy-Martian regolith composites with respect to heavy charged particles characteristic of the GCR ions which bombard the Martian surface. The composites were prepared at NASA Langley Research Center using simulated Martian regolith, in the process also evaluating fabrication methods which could lead to technologies for in situ fabrication on Mars. Initial evaluation of the radiation shielding properties is made using radiation transport models developed at NASA-LaRC, and the results of these calculations are used to select the composites with the most favorable radiation transmission properties. These candidates are then evaluated at particle accelerators which produce beams of heavy charged particles representative in energy and charge of the radiation at the surface of Mars. The ultimate objective is to develop the models into a design tool for use by mission planners, flight surgeons and radiation health specialists.

Miller, Jack↗

NASA NTRS2016

Strain-Detecting Composite Materials

A composite material includes a structural material and a shape-memory alloy embedded in the structural material. The shape-memory alloy changes crystallographic phase from austenite to martensite in response to a predefined critical macroscopic average strain of the composite material. In a second embodiment, the composite material includes a plurality of particles of a ferromagnetic shape-memory alloy embedded in the structural material. The ferromagnetic shape-memory alloy changes crystallographic phase from austenite to martensite and changes magnetic phase in response to the predefined critical macroscopic average strain of the composite material. A method of forming a composite material for sensing the predefined critical macroscopic average strain includes providing the shape-memory alloy having an austenite crystallographic phase, changing a size and shape of the shape-memory alloy to thereby form a plurality of particles, and combining the structural material and the particles at a temperature of from about 100-700.degree. C. to form the composite material.

Wallace, Terryl A.↗

NASA NTRS2015

Using Dust from Asteroids as Regolith Microsamples

Meteorite science is rich with compositional indicators by which we classify parent bodies, but few sample groups are definitively linked with asteroid spectra. More robust links need to be forged between meteorites and their parent bodies to understand the composition, diversity and distribution. A major link can be sample analysis of the parent body material and comparison with meteorite data. Hayabusa, the first sample return mission of the Japanese Aerospace Exploration Agency (JAXA), was developed to rendezvous with and collect samples from asteroid Itokawa and return them to Earth. Thousands of sub-100 micron particles were recovered, apparently introduced during the spacecraft impact into the surface of the asteroid, linking the asteroid Itokawa to LL chondrites [1]. Upcoming missions Hayabusa 2 and OSIRIS-REx will collect more significant sample masses from asteroids. In all these cases, the samples are or will be a collection of regolith particles. Sample return to earth is not the only method for regolith particle analysis. Dust is present around all airless bodies, generated by micrometeorite impact into their airless surfaces, which in turn lofts regolith particles into a "cloud" around the body. The composition, flux, and size-frequency distribution of dust particles can provide significant insight into the geological evolution of airless bodies [2]. For example, the Cassini Cosmic Dust Analyzer (CDA) detected salts in Enceladus' icy plume material, providing evidence for a subsurface ocean in contact with a silicate seafloor [3]. Similar instruments have flown on the Rosetta, LADEE, and Stardust missions. Such an instrument may be of great use in obtaining the elemental, isotopic and mineralogical composition measurement of dust particles originating from asteroids without returning the samples to terrestrial laboratories. We investigated the ability of a limited sample analysis capability using a dust instrument to forge links between asteroid regolith particles and known meteorite groups. We further set limits on the number of individual particles statistically needed to robustly reproduce a bulk composition.

microsamples↗

DOE OSTI2022

Preparation of SBA-15-Supported Metals by Vapor-Phase Infiltration

A simple method is presented for incorporating various catalytic metals into the pores of SBA-15 using vapor-phase infiltration. The precursors used in Atomic Layer Deposition (ALD) for Pt, Pd, Rh, Ru, and Ni were exposed to an evacuated SBA-15, resulting in monolayer films of the adsorbed precursors inside the mesopores. The metal particles that formed after removal of the precursor ligands remained in the pores and had particle sizes ranging from 3.8 nm for Pt to 5.2 nm for Ni, as determined by Transmission Electron Microscopy (TEM), XRD, and CO chemisorption. Metal loadings for saturation exposures ranged from 5.1-wt% for Ni to 9.1-wt% for Pt; however, uniform deposition was demonstrated for lower loadings of Pd by decreasing the amount of precursor. To determine the effect of the surface composition of the mesopores, Pd particles were also added to SBA-15 that was coated with a 0.2-nm film of ZrO2.

Rh↗

DOE OSTI2020

Barium Chloride Based Pyrotechnic Compositions for Green Color Emissions

Here, we present research focusing on the green light emission using Barium chloride dihydrate (BaCl2.2H2O) as an emitter contrary to commonly used Ba(NO3)2, Ba(ClO3)2, BaCO3, etc. For this work, different compositions containing BaCl2.2H2O and other components acting as oxidant, fuel, etc. were made and analyzed using TGA and burning tests. The flame intensity was captured using a photocell attached with a green color filter. It was observed that the decomposition behavior and the flame intensity were strongly influenced by the ratio of barium chloride to the oxidizer and by the particle size of the pyrotechnic composition powder. Compositions having a higher amount of oxidizer were found to decompose faster and have a more intense flame color.

Kanitkar, Swarom↗

NASA NTRS2001

Improved Spacecraft Materials for Radiation Protection

Methods by which radiation shielding is optimized need to be developed and materials of improved shielding characteristics identified and validated. The galactic cosmic rays (GCR) are very penetrating and the energy absorbed by the astronaut behind the shield is nearly independent of shield composition and even the shield thickness. However, the mix of particles in the transmitted beam changes rapidly with shield material composition and thickness. This results in part from the breakup of the high-energy heavy ions of the GCR which make contributions to biological effects out of proportion to their deposited energy. So the mixture of particles in the radiation field changes with shielding and the control of risk contributions from dominant particle types is critical to reducing the hazard to the astronaut. The risk of biological injury for a given particle type depends on the type of biological effect and is specific to cell or tissue type. Thus, one is faced with choosing materials which may protect a given tissue against a given effect but leave unchanged or even increase the risk of other effects in the same tissue or increase the risks to other adjacent tissues of a different type in the same individual. The optimization of shield composition will then be tied to a specific tissue and risk to that tissue. Such peculiarities arise from the complicated mixture of particles, the nature of their biological response, and the details of their interaction with material constituents. Aside from the understanding of the biological response to specific components, one also needs an accurate understanding of the radiation emerging from the shield material. This latter subject has been a principal element of this project. In the past ten years our understanding of space radiation interactions with materials has changed radically, with a large impact on shield design. For example, the NCRP estimated that only 2 g/sq cm. of aluminum would be required to meet the annual 500 mSv limit for the exposure of the blood forming organs (this limit is strictly for LEO but can be used as a guideline for the Mars mission analysis). The current estimates require aluminum shield thicknesses above 50 g/sq cm., which is impractical. In such a heavily shielded vehicle, the neutrons produced throughout the vehicle also contribute significantly to the exposure and this demands greater care in describing the angular dependence of secondary particle production processes. As such the continued testing of databases and transport procedures in laboratory and spaceflight experiments has continued. This has been the focus of much of the last year's activity and has resulted in improved neutron prediction capability. These new methods have also improved our understanding of the surface environment of Mars. The Mars 2003 NRA HEDS related surface science requirements were driven by the need to validate predictions on the upward flux of neutrons produced in the Martian regolith and bedrock made by the codes developed under this project. The codes used in the surface environment definition are also being used to look at in situ resources for the development of construction material for Martian surface facilities. For example, synthesis of polyimides and polyethylene as binders of regolith for developing basic structural elements has been studied and targets built for accelerator beam testing of radiation shielding properties. Preliminary mechanical tests have also been promising. Improved spacecraft materials have been identified (using the criteria reported by this project at the last conference) as potentially important for future shielding materials. These are liquid hydrogen, hydrogenated nanofibers, liquid methane, LiH, Polyethylene, Polysulfone, and Polyetherimide (in order of decreasing shield performance). Some of the materials are multifunctional and are required for other onboard systems. We are currently preparing software for trade studies with these materials relative to the Mars Reference Mission as required in the project's final year.

Wilson, John W.↗

NASA NTRS1997

Particle Characterization in Rocket Exhaust Plumes

A method to characterize particles in rocket exhaust plumes is developed. The particle velocity, size, and material composition are determined from crater characteristics resulting from impacts into aluminum and copper targets passed through the plume. The targets are mounted on a steel arm approximately 21 inches (53 cm) long which is rotated through the plume at sufficient velocity to prevent material failure resulting from thermal effects. A Scanning Electron Microscope (SEM) with secondary x-ray detectors is used to determine the particle material, and a standard optical measurement microscope is used to determine the crater diameter and depth. The crater diameter and depth are used in turn, as inputs to a ballistics computer code to estimate the velocity and size of the particle. The target has a safe residence time in the plume of approximately 50 ms before reaching an unacceptably high temperature. The = must mach a velocity of 104 ft/s (32 m/s) before entering the plume to produce the design residence time of 20 ms. The arm is actuated by a torsion spring with a 5-inch (13 cm) outer diameter, 0.625-inch (16 mm wire diameter, and 11 coils. A prototype of the entire rocket exhaust particle impact characterization system (PICS) was constructed and statically tested.

Callen, E. Eugene, Jr.↗

DOE OSTI2023

Achieving stable all-solid-state lithium-metal batteries by tuning the cathode-electrolyte interface and ionic/electronic transport within the cathode

All-solid-state batteries with sulfide electrolytes and high-nickel layered oxide cathodes attract much interest due to their high specific energy. However, their cycling performance is primarily influenced by the interface between the sulfide electrolyte and the high-Ni layered oxide particles, which requires the use of composite cathodes with high ionic and electronic conductivities to achieve a kinetically stable interface inside the cathode. Here, we apply Ti 2 O 3 particles to the high-Ni cathode LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), where Ti 2 O 3 not only acts as an electronic conductor to provide a fast diffusion path for electrons in the composite cathode, but also absorbs the lattice oxygen released from NCM811 cathode during cycling, stabilizing the Li 6 PS 5 Cl/NCM811 interface and suppressing electrolyte oxidation. The as-modified cathode exhibits an initial specific capacity of 192 mAh g -1 and retains 166 mAh g -1 after 140 cycles at 0.1C rate with a good capacity retention of 86.5%. Furthermore, the composite cathode displays high rate capability even at 1C rate. By contrast, the unmodified Li 6 PS 5 Cl/NCM811 cathode shows poor cycling performance with only 130 mAh g -1 remaining after 130 cycles. This work provides a new direction for the design of cathodes for all-solid-state batteries that can deliver high specific energy with long cycle life.

25 ENERGY STORAGE↗

NASA NTRS1994

Further analysis of remnants found in LDEF and Mir impact craters

This study is the further investigation of space-exposed samples recently recovered from the American satellite LDEF and the Franco-Soviet Mir 'Aragatz' experiment. Some interesting impact features have been selected as examples to demonstrate various findings. Part of the objective of the experiments was to determine the nature and origin of particles in low earth orbit (LEO). Observations show that the 'multiple foil detectors' appear to be an effective way of retaining impactor residues of larger particles. They provide a 'witness' foil that shows the shape and dimensions of the impacting particle. Several low-velocity (less than 4 km/s) oblique craters containing significant quantities of impactor residue have been identified. Energy dispersive spectrometer (EDS) analyses of the residues show evidence of micrometeoroid and debris compositions. Similarities between the meteoroid signatures and those of Brownlee particles have been noted. Evidence of at least two different grain compositions in one impacting particle is shown. The discovery of debris impacts on the trailing edge of LDEF demonstrates that artificial debris may be found, not just in circular orbits, but also in elliptical orbits.

Berthoud, S. Lucinda↗

NASA NTRSDate not supplied

Microstructure Quantification and Random Forest Regression Models for Li4Ti5O12–Ni Property Prediction

All-solid-state structural lithium-ion batteries are sought to enable all-electric propulsion in next generation aerospace concepts through improved safety and systems level weight savings. In this work, the influence of processing conditions on microstructural evolution was evaluated for anode composites of strain-free Li4Ti5O12 and metallic nickel current collector. Beyond size distributions, this study explored methods of quantifying microstructural features that describe changes in the spatial distribution and coalescence of nickel particles as a function of sample composition and sintering conditions. Processing-microstructure-property relationships were described by microstructure quantifiers including nickel particle count per area, nearest neighbor distance distribution, and edge-to-edge distance distribution. Machine learning methods were applied to compare the relative influence of processing conditions and microstructural features on electrical conductivity and mechanical strength to optimize for simultaneous energy storage and load bearing performance. Insights gained from this work inform future evaluation of alternative energy storage materials and microstructures for multifunctional performance, and generation of microstructural descriptors strengthens modeling across length scales.

anode↗

NASA NTRS2018

Impact of Powder Variability on the Microstructure and Mechanical Behavior of Selective Laser Melted Alloy 718

Powder-bed additive manufacturing processes use fine powders to build parts layer-by-layer. Alloy 718 powder feedstocks for selective laser melting (SLM) additive manufacturing are produced commercially by both gas and rotary atomization and are available typically in the 10-45 or 15-45 microns size ranges. A comprehensive investigation was conducted to understand the impact of powder variability on the microstructure and mechanical behavior of SLM 718 heat treated to Aerospace Material Specification (AMS) 5664. This study included sixteen virgin powders and three once-recycled powders within the 10-45 and 15-45 microns size ranges that were obtained from seven direct source suppliers and one reseller. Although alike as highly regular spheroids, these powders showed distinct differences in composition (especially Al, C and N contents), particle size distributions, and powder features such as degree of agglomeration, fusion and surface roughness. Compositional differences expectedly had the strongest impact on microstructure. High N and C contents formed TiN-nitrides and/or (Nb,Ti,Mo)-C carbides on the grain boundaries, prevented recrystallization during heat treatment, and resulted in retained (001)-scalloped shaped grains that ranged from 19 to 41 microns in average size. In the absence of this particle pinning, the average grain size of the heat treated SLM 718 ranged from 51 microns to 90 microns. Room temperature tensile and high cycle fatigue (HCF) testing compared as-fabricated (AF) and low stress ground (LSG) surface conditions. Tensile testing revealed consistent behavior between the two surface conditions and amongst the powder lots. The finer grained SLM 718 builds displayed the lowest tensile properties. A SLM 718 build fabricated from a powder with eight times lower C content showed statistically better tensile properties presumably due to enhanced coarsening of (delta)-Ni3Nb precipitates. The specimens from once-recycled powders had slightly higher tensile strengths and slightly higher ductility compared to their virgin equivalents; once-recycling also did not substantially degrade the mean HCF life. The LSG fatigue lives agreed with conventionally manufactured 718 data, while AF lives exhibited a knock-down due to surface roughness. The fatigue lives of AF specimens were statistically equivalent across powder lots except for one and failures typically initiated at stress concentrators associated with SLM surface asperities. Fatigue testing of low stress ground specimens result in both transgranular and within facet crack initiations. More than half of the cracks initiated from these facets for the machined condition; however, these facets appeared to be within grains that were larger-than-average in size. A nitrogen-atomized powder with fine prior particles of TiN-nitrides and M(Ti,Nb,Mo)C carbides from atomization on powder surfaces resulted in the best fatigue performance with segregation of these particles to the SLM 718 grain boundaries leading to higher resistance to early-stage crack propagation. Typically the fine-grained builds with minor phases along the grain boundaries did not perform well in fatigue, whereas a larger-grain build with lower carbon content and coarser delta-Ni3Nb precipitates showed the next best HCF response. Further details of the build microstructure and its impact on tensile and fatigue behavior was considered.

laser deposition↗

DOE OSTI2024

Recycling of additively printed anisotropic Nd-Fe-B bonded magnets

A high potential cost-effective and environmentally friendly method has been applied for recycling anisotropic Nd-Fe-B bonded magnets. Waste additively printed Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) Nd-Fe-B anisotropic bonded magnet was pulverized into composite powder containing Nd-Fe-B particles and nylon binder through cryomilling at a liquid nitrogen temperature (~77 K) under Ar inert atmosphere. Then, the cryomilled composite powder was warm compacted into a bonded magnet. Further, the magnetic particles were aligned during post-compaction annealing under a magnetic field of 30 kOe. The recycled bonded magnets have a higher density (3% enhancement), but slightly inferior magnetic properties compared to the original magnets, i.e., the magnetic remanence, coercivity and maximum energy product are reduced by 2%, 3% and 8%, respectively. The scanning electron microscopy revealed that some HDDR Nd-Fe-B powder crumbled into fine particles during cryomilling. Powder X-ray diffraction showed a small amount of Nd-oxide impurity in the cryomilled powder. The slightly deteriorated magnetic properties are ascribed to the oxidation of Nd-Fe-B particles due to formation of fresh fracture surface during cryomilling. The approach enables the direct reuse of end-of-life bonded magnets in an economical and environmentally friendly way.

36 MATERIALS SCIENCE↗

NASA NTRS1984

Sulfur dioxide and particles in quiescent volcanic plumes from Poas, Arenal, and Colima volcanos, Costa Rica and Mexico

Measurements of SO2 emission rates and concentrations and of particle distribution, size, shape, and composition were made in quiescent volcanic plumes emitted into the troposphere from Poas and Arenal volcanos, Costa Rica, and Colima volcano, Mexico. SO2 emission rates were 700 + or - 180 metric tons per day (t/d) for Poas, 210 + or - 30 t/d for Arenal, and 320 + or - 50 t/d for Colima. The concentrations of SO2 calculated from the COSPEC/lidar data were 5-380 ppb. Concentrations of SO2 measured directly by flame photometry were 10-250 ppb. Particles collected in the plumes with a quartz crystal microbalance impactor were mostly less than 3 microns in diameter and consisted of droplets of dilute sulfur-bearing solutions and minor amounts of layer silicate particles coated with a sulfur-bearing film or crust. Total particle concentrations were 4.7 micrograms per cu.m for Poas and 18.8 micrograms per cu.m for Colima. Comparison of concentrations of SO2 in the plumes with gas samples collected at fumaroles on the ground suggests that the plumes are diluted by the atmosphere by factors of up to 100,000.

Casadevall, T. J.↗

NASA NTRS1978

Ion microprobe analyses of aluminous lunar glasses - A test of the 'rock type' hypothesis

Previous soil survey investigations found that there are natural groupings of glass compositions in lunar soils and that the average major element composition of some of these groupings is the same at widely separated lunar landing sites. This led soil survey enthusiasts to promote the hypothesis that the average composition of glass groupings represents the composition of primary lunar 'rock types'. In this investigation the trace element composition of numerous aluminous glass particles was determined by the ion microprobe method as a test of the above mentioned 'rock type' hypothesis. It was found that within any grouping of aluminous lunar glasses by major element content, there is considerable scatter in the refractory trace element content. In addition, aluminous glasses grouped by major elements were found to have different average trace element contents at different sites (Apollo 15, 16 and Luna 20). This evidence argues that natural groupings in glass compositions are determined by regolith processes and may not represent the composition of primary lunar 'rock types'.

Meyer, C., Jr.↗

NASA NTRS2005

Improved Anode for a Direct Methanol Fuel Cell

A modified chemical composition has been devised to improve the performance of the anode of a direct methanol fuel cell. The main feature of the modified composition is the incorporation of hydrous ruthenium oxide into the anode structure. This modification can reduce the internal electrical resistance of the cell and increase the degree of utilization of the anode catalyst. As a result, a higher anode current density can be sustained with a smaller amount of anode catalyst. These improvements can translate into a smaller fuel-cell system and higher efficiency of conversion. Some background information is helpful for understanding the benefit afforded by the addition of hydrous ruthenium oxide. The anode of a direct methanol fuel cell sustains the electro-oxidation of methanol to carbon dioxide in the reaction CH3OH + H2O--->CO2 + 6H(+) + 6e(-). An electrocatalyst is needed to enable this reaction to occur. The catalyst that offers the highest activity is an alloy of approximately equal numbers of atoms of the noble metals platinum and ruthenium. The anode is made of a composite material that includes high-surface-area Pt/Ru alloy particles and a proton-conducting ionomeric material. This composite is usually deposited onto a polymer-electrolyte (proton-conducting) membrane and onto an anode gas-diffusion/current-collector sheet that is subsequently bonded to the proton-conducting membrane by hot pressing. Heretofore, the areal density of noble-metal catalyst typically needed for high performance has been about 8 mg/cm2. However, not all of the catalyst has been utilized in the catalyzed electro-oxidation reaction. Increasing the degree of utilization of the catalyst would make it possible to improve the performance of the cell for a given catalyst loading and/or reduce the catalyst loading (thereby reducing the cost of the cell). The use of carbon and possibly other electronic conductors in the catalyst layer has been proposed for increasing the utilization of the catalyst by increasing electrical connectivity between catalyst particles. However, the relatively low density of carbon results in thick catalyst layers that impede the mass transport of methanol to the catalytic sites. Also, the electrical conductivity of carbon is less than 1/300th of typical metals. Furthermore, the polymer-electrolyte membrane material is acidic and most metals are not chemically stable in contact with it. Finally, a material that conducts electrons (but not protons) does not contribute to the needed transport of protons produced in the electro-oxidation reaction.

Valdez, Thomas↗