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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Cyclic variations in nitrogen uptake rate of soybean plants: effects of pH and mixed nitrogen sources

To determine if the daily pattern of NO3- and NH4+ uptake is affected by acidity or NO3- : NH4+ ratio of the nutrient solution, non-nodulated soybean plants (Glycine max) were exposed for 21 days to replenished, complete nutrient solutions at pH 6.0, 5.5, 5.0, and 4.5 which contained either 1.0 mM NH4+, 1.0 mM NO3- [correction of NO3+], 0.67 mM NH4+ plus 0.33 mM NO3- (2:1 NH4+ : NO3-) [correction of (2:1 NH3+ : NO4-)], or 0.33 mM NH4+ plus 0.67 mM NO3- (1:2 NH4+ : NO3-). Net uptake rates of NH4+ and NO3- were measured daily by ion chromatography as depletion from the replenished solutions. When NH4+ and NO3- were supplied together, cumulative uptake of total nitrogen was not affected by pH or solution NH4+ : NO3- ratio. The cumulative proportion of nitrogen absorbed as NH4+ decreased with increasing acidity; however, the proportional uptake of NH4+ and NO3- was not constant, but varied day-to-day. This day-to-day variation in relative proportions of NH4+ and NO3- absorbed when NH4+ : NO3- ratio and pH of solution were constant indicates that the regulatory mechanism is not directly competitive. Regardless of the effect of pH on cumulative uptake of NH4+, the specific nitrogen uptake rates from mixed and from individual NH4+ and NO3- sources oscillated between maxima and minima at each pH with average periodicities similar to the expected interval of leaf emergence.

Non-NASA Center↗
DOE OSTI2020

Parametric study of operating conditions of an SO 2 -depolarized electrolyzer

Large-scale hydrogen generation is needed to satisfy both existing commercial demands and the realization of a hydrogen economy. The hybrid sulfur cycle has the potential to meet this goal without the use of fossil fuels. The ability to model and predict how the electrolyzer step of the cycle is affected by independent and interdependent variables is vital to maximizing the efficiency of the overall cycle. Herein, we report that our parametric study of the SO 2 -depolarized electrolyzer, representing one half of the overall reaction cycle, has identified desirable conditions and will help guide further development for operation that will achieve the benchmarks for economic feasibility. We discuss the interactions among the inlet flow rates, applied current, and cell temperature and pressure, on the resulting cell voltage and acid concentration in the liquid product stream. For example, we find that using a sulfonated polybenzimidazole (s-PBI) membrane and a platinum catalyst, a constant current density of either 0.5 A cm -2 , 0.75 A cm -2 , or 1 A cm -2 with an acid concentration of 65 wt% H 2 SO 4 can be produced at a cell voltage of 0.59 V, 0.63 V, and 0.67 V, respectively, by maintaining a cell temperature of 130 °C, a pressure of 2 bar, and a water-to-SO 2 stoichiometry of 2.77. Finally, we discuss directions for future research based on the findings in this manuscript.

08 HYDROGEN↗
NASA NTRS1984

Binding constants of phenylalanine for the four mononucleotides

Earlier work has shown that several properties of amino acids correlate directly with properties of their anticodonic nucleotides. Furthermore, in precipitation studies with thermal proteinoids and homopolyribonucleotides, an anticodonic preference was displayed between Lys-rich, Pro-rich and Gly-rich thermal proteinoids and their anticodonic polyribonucleotides. However, Phe-rich thermal proteinoid displayed a preference for its codonic nucleotide, poly U. This inconsistency seemed to be explained by a folding in of the hydrophobic residues of Phe causing the proteinoid to appear more hydrophilic. The present work used nuclear magnetic resonance techniques to resolve a limited question: to which of the four nucleotides does Phe bind most strongly? The results show quite clearly that Phe binds most strongly to its anticodonic nucleotide, AMP.

Khaled, M. A.↗
DOE OSTI2021

High-performance SO 2 -depolarized electrolysis cell using advanced polymer electrolyte membranes

Three different proton conducting polymeric membrane materials (Nafion® 115, Nafion® 212, and sulfonated Diels-Alder polyphenylene [SDAPP]) were evaluated for use in SO 2 -depolarized electrolyzers for the production of hydrogen via the hybrid sulfur cycle. Their performance was measured using different water feed strategies to minimize overpotential losses while maintaining high product acid concentration. Both thin membranes (Nafion® 212 and SDAPP) showed performance superior to that of the thicker Nafion® 115. Here, the SDAPP membrane electrode assembly (MEA) performed well at higher acid concentrations, maintaining low ohmic and kinetic overpotentials. Finally, short-term (100-h) stability tests under constant current conditions showed minimal degradation for the SDAPP and Nafion® 212 MEAs. SDAPP MEA performance approached the targets needed to make the hybrid sulfur cycle a competitive process for hydrogen production (product acid concentration ≥65 wt% H 2 SO 4 at ≤ 0.6-V cell potential and ≥0.5 A-cm –2 current density).

08 HYDROGEN↗
NASA NTRS1980

Pulse charging of lead-acid traction cells

Pulse charging, as a method of rapidly and efficiently charging 300 amp-hour lead-acid traction cells for an electric vehicle application was investigated. A wide range of charge pulse current square waveforms were investigated and the results were compared to constant current charging at the time averaged pulse current values. Representative pulse current waveforms were: (1) positive waveform-peak charge pulse current of 300 amperes (amps), discharge pulse-current of zero amps, and a duty cycle of about 50%; (2) Romanov waveform-peak charge pulse current of 300 amps, peak discharge pulse current of 15 amps, and a duty of 50%; and (3) McCulloch waveform peak charge pulse current of 193 amps, peak discharge pulse current of about 575 amps, and a duty cycle of 94%. Experimental results indicate that on the basis of amp-hour efficiency, pulse charging offered no significant advantage as a method of rapidly charging 300 amp-hour lead-acid traction cells when compared to constant current charging at the time average pulse current value. There were, however, some disadvantages of pulse charging in particular a decrease in charge amp-hour and energy efficiencies and an increase in cell electrolyte temperature. The constant current charge method resulted in the best energy efficiency with no significant sacrifice of charge time or amp-hour output. Whether or not pulse charging offers an advantage over constant current charging with regard to the cell charge/discharge cycle life is unknown at this time.

Smithrick, J. J.↗
DOE OSTI2022

Salinity and hydraulic retention time induce membrane phospholipid acyl chain remodeling in Halanaerobium congolense WG10 and mixed cultures from hydraulically fractured shale wells

Bacteria remodel their plasma membrane lipidome to maintain key biophysical attributes in response to ecological disturbances. For Halanaerobium and other anaerobic halotolerant taxa that persist in hydraulically fractured deep subsurface shale reservoirs, salinity, and hydraulic retention time (HRT) are important perturbants of cell membrane structure, yet their effects remain poorly understood. Membrane-linked activities underlie in situ microbial growth kinetics and physiologies which drive biogeochemical reactions in engineered subsurface systems. Hence, we used gas chromatography–mass spectrometry (GC–MS) to investigate the effects of salinity and HRT on the phospholipid fatty acid composition of H. congolense WG10 and mixed enrichment cultures from hydraulically fractured shale wells. We also coupled acyl chain remodeling to membrane mechanics by measuring bilayer elasticity using atomic force microscopy (AFM). For these experiments, cultures were grown in a chemostat vessel operated in continuous flow mode under strict anoxia and constant stirring. Our findings show that salinity and HRT induce significant changes in membrane fatty acid chemistry of H. congolense WG10 in distinct and complementary ways. Notably, under nonoptimal salt concentrations (7% and 20% NaCl), H. congolense WG10 elevates the portion of polyunsaturated fatty acids (PUFAs) in its membrane, and this results in an apparent increase in fluidity (homeoviscous adaptation principle) and thickness. Double bond index (DBI) and mean chain length (MCL) were used as proxies for membrane fluidity and thickness, respectively. These results provide new insight into our understanding of how environmental and engineered factors might disrupt the physical and biogeochemical equilibria of fractured shale by inducing physiologically relevant changes in the membrane fatty acid chemistry of persistent microbial taxa. GRAPHICAL ABSTRACT Salinity significantly alters membrane bilayer fluidity and thickness in Halanaerobium congolense WG10.

03 NATURAL GAS↗
NASA NTRS1995

Spectroscopic Evidence Against Nitric Acid Trihydrate in Polar Stratospheric Clouds

Heterogeneous reactions on polar stratospheric clouds (PSC's) play a key role in the photochemical mechanism thought to be responsible for ozone depletion in the Antarctic and Arctic. Reactions of PSC particles activate chlorine to forms that are capable of photochemical ozone destruction, and sequester nitrogen oxides (NOx) that would otherwise deactivate the chlorine. Although the heterogeneous chemistry is now well established, the composition of the clouds themselves is uncertain. It is commonly thought that they are composed of nitric acid trihydrate, although observations have left this question unresolved. Here we reanalyse infrared spectra of type 1 PSCs obtained in Antarctica in September 1987, using recently measured optical constants of the various compounds that might be present in PSCs. We find these PSCs were not composed of nitric acid trihydrate but instead had a more complex compositon, perhaps that of a ternary solution. Because cloud formation is sensitive to their composition, this finding will alter our understanding of the locations and conditions in which PSCs form. In addition, the extent of ozone loss depends on the ability of the PSCs to remove NOx permanently through sedimentation, The sedimentation rates depend on PSC particle size which in turn is controlled by the composition and formation mechanism.

Toon, Owen B.↗
DOE OSTI2020

Spectroscopic characterization of a new Re(i) tricarbonyl complex with a thiosemicarbazone derivative: towards sensing and electrocatalytic applications

This work describes the preparation of a new thiosemicarbazone derivative, (Z)- N -ethyl-2-(6-oxo-1,10-phenanthrolin-5(6 H )-ylidene)hydrazinecarbothioamide (phet) and its respective Re( I ) tricarbonyl chloro complex, fac -[ReCl(CO) 3 (phet)]. The spectroscopic, photophysical and electrochemical properties of the new complex were fully investigated through steady state and time-resolved techniques along with computational calculations. In fac -[ReCl(CO) 3 (phet)], the new ligand is coordinated to the metal center through the pyridyl rings of the phenanthroline moiety. The unbound electron pairs in the S atom of the bending thiosemicarbazone group induce new low energy lying electronic transitions. Consequently, enhanced visible light absorption up to 550 nm is observed in acetonitrile due to the overlap between MLCT Re→phet and IL phet(n→π*) transitions. The absorption bands and emission quantum yields of fac -[ReCl(CO) 3 (phet)] are sensitive to proton concentration due to an acid-basic equilibrium in the N atoms of the thiosemicarbazone. Proton dissociation constants of 10.0 ± 0.1 and 11.4 ± 0.2 were determined respectively for the ground and excited states of the new complex. Spectral changes could also be observed in the presence of Zn 2+ cations which can be further explored for sensing applications. The electrochemical behavior of the new complex was studied in detail, revealing up to four one electron reduction processes in the range from 0 to -2.4 V vs. Fc + /Fc. With support of DFT calculations, the first three processes are ascribed to the reduction of the coordinated phet ligand followed by the Re I/0 reduction and consequent Cl - release. Furthermore, the new complex was able to act as an electrocatalyst for CO 2 reduction into CO ( E onset = -1.92 V vs. Fc + /Fc), with a turnover frequency of 2.81 s -1 and turnover number of 24 ± 1 in anhydrous acetonitrile, being the first Re( I ) tricarbonyl complex with a thiosemicarbazone derivative described for this goal. The detailed characterization carried out here can drive the development of new Re( I )-thiosemicarbazone derivatives for different applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

Low dielectric thermoplastic polyimide resin

NASA-Langley studies of polymer structure-property relationships have led to the development of a method for the reduction of dielectric constants in polyimides through chemical alterations of polymer backbone composition to reduce chain-chain electronic interactions, as well as through the incorporation of fluorine atoms into the polymer molecular structure. Still-greater dielectric constant reductions are obtainable by means of a physical incorporation of diamic acid additives into these low-dielectric polyimide systems; the resulting thermoplastic resins are applicable to polymer matrices for composite structural materials.

Stoakley, D. M.↗
DOE OSTI2023

Lewis Acids and Electron-Withdrawing Ligands Accelerate CO Coordination to Dinuclear Cu I Compounds

A series of dinuclear molecular copper complexes were prepared and used to model the binding and Lewis acid stabilization of CO in heterogeneous copper CO 2 reduction electrocatalysts. Experimental studies (including measurement of rate and equilibrium constants) and electronic structure calculations suggest that the key kinetic barrier for CO binding may be a σ-interaction between CuI and the incoming CO ligand. The rate of CO coordination can be increased upon the addition of Lewis acids or electron-withdrawing substituents on the ligand backbone. Conversely, K eq for CO coordination can be increased by adding electron density to the metal centers of the compound, consistent with stronger π-backbonding. Lastly, the electrochemically measured kinetic results were mapped onto an electrochemical zone diagram to illustrate how these system changes enabled access to each zone.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Fouling characterization and treatment of water reuse concentrate with membrane distillation: Do organics really matter

Membrane distillation (MD) for the treatment of concentrated brines has been limited in part by membrane fouling, resulting in subsequent flux decline and membrane wetting. This study provides new insight into the identification of fouling and scaling mechanisms and pretreatment strategies for mitigating flux decline with MD treatment of water reuse reverse osmosis concentrate (ROC). Bench-scale direct contact MD experiments were performed with untreated and pretreated ROC. Biological activated carbon (BAC), chemical water softening, or fluidized bed crystallization reactor coupled with ion exchange (FBCR-IX) were selected as pretreatment strategies to isolate the effects of organic fouling and calcium scaling. Organic and inorganic compounds were analyzed by high-performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Calcium ions were found to be the major contributor to flux decline despite the high organic content in the ROC. Minimal organic fouling is likely because the organic matter in the ROC is hydrophilic, limiting hydrophobic-hydrophobic interactions between the organics and the membrane. Furthermore, the water flux declined by 63 % after removing organic compounds by BAC pretreatment, with 60 % of the calcium mass precipitating from the solution. Whereas, the water flux remained constant after removing multivalent ions with fluidized bed crystallization. Cleaning the membrane by acid washing and temperature reversal recovered 73 % and 12 % of the water flux, respectively. The analyses outlined in this study can assist in selecting appropriate fouling and scaling mitigation strategies for water reuse ROC and a wide range of feed solutions used in MD applications.

42 ENGINEERING↗
DOE OSTI2024

Structure Sensitive Reaction Kinetics of Chiral Molecules on Intrinsically Chiral Surfaces

Enantiospecific heterogeneous catalysis utilizes chiral surfaces to resolve enantiomers via structure sensitive surface chemistry. The catalyst design challenge is the identification of chiral surface structures that maximize enantiospecificity. Herein, we develop data driven models for the enantiospecificity of tartaric acid reactions on chiral Cu(hkl) R&S surfaces. Measurements of enantiospecific rate constants were obtained by using curved Cu(hkl) R&S surfaces that enable kinetic measurements on hundreds of chiral surface orientations. One model uses feature vectors derived from generalized coordination numbers to capture the local structure around Cu atoms exposed by the Cu(hkl) R&S surfaces. The second model introduces the use of chiral cubic harmonic functions to capture the symmetry constraints of the face-centered cubic Cu structure. The model using 58 generalized coordination numbers has a fitting error similar to that of the model using only 5 cubic harmonic functions. The two models predict maxima in the enantiospecificity on surfaces with very similar surface orientations. The models developed in this work are applicable for any enantiospecific reaction happening on any chiral material with a cubic lattice structure, opening the way to understanding the surface structure sensitivity of the enantiospecific reaction kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Stability of plutonium oxide nanoparticles in the presence of montmorillonite and implications for colloid facilitated transport

The physical and chemical stability of PuO 2 nanoparticles (intrinsic colloids) in groundwater will control their transport and may affect the performance of high-level radioactive waste repositories. In this study, we examined the chemical stability of two types of PuO 2 nanoparticles at both 25 and 80 °C. The “alkaline” PuO 2 nanoparticles were prepared by neutralizing an acidic Pu(IV) solution with dilute NaOH to pH ~9.5. The “acidic” PuO 2 nanoparticles were precipitated from 0.1 M nitric acid by heating a Pu(IV) solution at 60–80 °C for 30 min. The chemical stability of these PuO 2 nanoparticles was tested in the presence of montmorillonite, a common mineral in the environment and potentially relevant backfill material in some nuclear waste repository designs. The “alkaline” PuO 2 nanoparticles were found to be unstable over a timescale of months at both 25 and 80 °C, with elevated temperature enhancing their dissolution rates and sorption to montmorillonite. PuO 2 nanoparticle dissolution rates decreased with increasing Pu concentration, consistent with solution saturation. The “acidic” PuO 2 nanoparticles appeared to remain stable for much longer than the “alkaline” PuO2 nanoparticles. The “alkaline” PuO 2 nanoparticle dissolution rate constants were as high as 10 -11.9±0.4 mol m -2 s -1 and 10 -11.2±0.2 mol m -2 s -1 at 25 and 80 °C, respectively, while the “acidic” PuO 2 nanoparticle dissolution rate at 80 °C was 10 -13.5 mol m -2 s -1 . Based on transmission electron microscopy, the “alkaline” and “acidic” PuO 2 nanoparticles were of similar size (2.5–4.5 and 2–3 nm nanoparticles, respectively). However, the “acidic” PuO 2 nanoparticles formed more ordered nanoparticle aggregates. Our results suggest that the specific conditions experienced during PuO 2 nanoparticle formation could significantly affect the stability of PuO 2 in the presence of competing sorption processes and, in turn, the relative importance of intrinsic versus pseudocolloid transport in the environment.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS2003

Modeling Aerosol Nucleation

The goal of this work has been to understand how nitric acid condenses on cirrus ice cloud particles by analyzing data obtained during the SAGE III Ozone Loss and Validation Experiment (SOLVE) research mission based out of Kiruna, Sweden. Ms. Gamblin simultaneously analyzed gas phase nitric acid data along with particulate NO, data, particulate, vapor and gas-phase water data from several different instruments, particle size data, which included surface area and volume measurements, ozone concentration data as well as temperature, pressure and GPS coordinates of the sampled air parcel. All parameters where held constant with only one allowed to vary in order to determine what controls the extent to which nitric acid will condensation on ice. In addition, this data was compared to theoretical values of nitric acid condensation on ice based upon recent laboratory data. Comparison of these two data sets shows the field data does not agree with what is expected in the laboratory at comparable temperatures and nitric acid pressures. The most significant difference is that surface coverages in the atmosphere were found to be elevated relative to surface coverages measured in the laboratory. The results of this study were accepted for publication by Geophysical Research Letters.

Toon, Owen B.↗
DOE OSTI2023

Low and High LET Degradation Studies of Metal-Loaded Organic Phase Ligands in the ALSEP Process

Organic solutions comprising the Actinide Lanthanide Separation Process (ALSEP) solvent consisting of 0.5 M 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and 0.05 M N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane were subjected to low LET and high LET irradiation before and after equilibration with an aqueous phase of 3 M HNO 3 . Degradation dose constants revealed greater ligand degradation due to gamma irradiation than alpha irradiation for both ligands. Furthermore, equilibration with nitric acid did not have a significant impact on ligand degradation for either irradiation source. Identified degradation products were similar for both gamma and alpha irradiation and occurred mostly through the rupture of the N–C carbonyl and C–O ether bonds for T2EHDGA and the C–Oether bond in HEH[EHP]. Acid contact appears to alter the degradation pathway by favoring the formation of higher molecular weight recombination products. Furthermore, mixed T2EHDGA-HEH[EHP]-NO 3 complexes were formed with Nd(III) after extraction from 3 M HNO 3 , and low LET gamma irradiation of the Nd(III) loaded organic solution produced similar degradation products as the organic solution absent of Nd(III). Interestingly, and likely due to the greater radiolytic susceptibility of T2EHDGA than HEH[EHP], a HEH[EHP]-Nd(III) complex appears to form as the T2EHDGA degrades with increasing absorbed dose.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1991

Effects of systemic carbidopa on dopamine synthesis in rat hypothalamus and striatum

Significant concentrations of carbidopa (CD) were found in rat hypothalamus, striatum, and in striatal microdialysis efflux after intraperitoneal administration of the drug. Efflux levels peaked one hour after administration of 100 mg/kg at 0.37 microg/kg or about 2 percent of serum levels. Concurrent CD levels in hypothalamus and striatum were about 2.5 percent and 1.5 percent, respectively, of corresponding serum levels. Levels of dopamine and its principal metabolites in striatal efflux were unaffected. The removal of the brain blood by saline perfusion decreased the striatal and hypothalamic CD concentrations only by 33 percent and 16 percent, respectively. In other rats receiving both CD and levodopa (LD), brain L-dopa, dopamine, and 3,4-dihydroxyphenvlacetic acid (DOPAC) levels after one hour tended to be proportionate to LD dose. When the LD dose remained constant, increasing the CD dose dose-dependently enhanced L-dopa levels in the hypothalamus and striatum. However, dopamine levels did not increase but, in contrast, decreased dose-dependently (although significantly only in the hypothalamus). CD also caused dose-dependent decrease in striatal 3-O-methyldopa (3-OMD) and in striatal and hypothalamic homovanillic acid (HVA), when the LD dose was 50 mg/kg. We conclude that, at doses exceedimg 50 mg/kg, sufficient quantities of CD enter the brain to inhibit dopamine formation, especially in the hypothalamus. Moreover, high doses of LD/CD, both of which are themselves catechols, can inhibit the O-methylation of brain catecholamines formed from the LD.

Kaakkola, S.↗
NASA NTRS1992

Effects of systemic carbidopa on dopamine synthesis in rat hypothalamus and striatum

Significant concentrations of carbidopa (CD) were found in rat hypothalamus, striatum, and in striatal microdialysis efflux after intraperitoneal administration of the drug. Efflux levels peaked one hour after administration of 100 mg/kg at 0.37 micrograms/ml, or about 2% of serum levels. Concurrent CD levels in hypothalamus and striatum were about 2.5% and 1.5%, respectively, of corresponding serum levels. Levels of dopamine and its principal metabolites in striatal efflux were unaffected. The removal of the brain blood by saline perfusion decreased the striatal and hypothalamic CD concentrations only by 33% and 16%, respectively. In other rats receiving both CD and levodopa (LD), brain L-dopa, dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels after one hour tended to be proportionate to LD dose. When the LD dose remained constant, increasing the CD dose dose-dependently enhanced L-dopa levels in the hypothalamus and striatum. However dopamine levels did not increase but, in contrast, decreased dose-dependently (although significantly only in the hypothalamus). CD also caused dose-dependent decrease in striatal 3-O-methyldopa (3-OMD) and in striatal and hypothalamic homovanillic acid (HVA), when the LD dose was 50 mg/kg. We conclude that, at doses exceeding 50 mg/kg, sufficient quantities of CD enter the brain to inhibit dopamine formation, especially in the hypothalamus. Moreover, high doses of LD/CD, both of which are themselves catechols, can inhibit the O-methylation of brain catecholamines formed from the LD.

NASA Discipline Regulatory Physiology↗
DOE OSTI2021

Investigations of the stability of etched or platinized p-InP(100) photocathodes for solar-driven hydrogen evolution in acidic or alkaline aqueous electrolytes

Here, the stability of p-InP photocathodes performing the hydrogen-evolution reaction (HER) has been evaluated in contact with either 1.0 M H 2 SO 4 (aq) or 1.0 M KOH(aq), with a focus on identifying corrosion mechanisms. Stability for the solar-driven HER was evaluated using p-InP electrodes that were either etched or coated with an electrodeposited Pt catalyst (p-InP/Pt). Variables such as trace O 2 were systematically controlled during the measurements. Changes in surface characteristics after exposure to electrochemical conditions as well as electrode dissolution processes were monitored using X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma mass spectrometry (ICP-MS). In either H 2 SO 4 or KOH, etched p-InP photoelectrodes corroded cathodically under illumination, forming metallic In 0 at the electrode surface. In contrast, electrodeposition of Pt kinetically stabilized illuminated p-InP photocathodes in both H 2 SO 4 and KOH by inhibiting the cathodic corrosion pathway. Notably, when held at 0 V vs. the reversible hydrogen electrode (RHE) in 1.0 M H 2 SO 4 (aq), p-InP/Pt exhibited a stable current density (J) of ~–18 mA cm –2 for >285 h under simulated 1 Sun illumination. The long-term current density vs. potential (J–E) behavior at pH 0 and pH 14 of p-InP/Pt photocathodes correlated with changes in the surface chemistry as well as the dissolution of p-InP. In acidic media, the J–E behavior of p-InP/Pt photocathodes remained nearly constant with time, but the surface of a p-InP/Pt electrodes gradually turned P-rich via a slow and continuous leaching of In ions. In alkaline electrolyte, the surface of p-InP/Pt electrodes was passivated by formation of an InO x layer that exhibited negligible dissolution but led to a substantial degradation in the J–E characteristics. Consequently, changes in the catalytic kinetics and surface stoichiometry are both important considerations for determining the corrosion chemistry and the long-term operational stability of InP photoelectrodes.

14 SOLAR ENERGY↗