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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: Competition between phonon confinement and strain-related effects

Raman scattering in combination with optical spectroscopy and structural studies by X-ray diffraction was employed to investigate the phonon confinement and strain-induced effects in 3D assemblies of variable-size zincblende ZnSe quantum dots close packed in thin film form. Nanostructured thin films were synthesized by colloidal chemical approach, while tuning of the nanocrystal size was enabled by post-deposition thermal annealing treatment. In-depth insights into the factors governing the observed trends of the position and half-width of the 1LO band as a function of the average QD size were gained. The overall shifts in the position of 1LO band were found to result from an intricate compromise between the influence of phonon confinement and lattice strain-induced effects. Both contributions were quantitatively and exactly modeled. Accurate assignments of the bands due to surface optical (SO) modes as well as of the theoretically forbidden transverse optical (TO) modes were provided, on the basis of reliable physical models (such as the dielectric continuum model of Ruppin and Englman). The size-dependence of the ratio of intensities of the TO and LO modes was studied and discussed as well. Relaxation time characterizing the phonon decay processes in as-deposited samples was found to be approximately 0.38 ps, while upon post-deposition annealing already at 200 °C it increases to about 0.50 ps. Both of these values are, however, significantly smaller than those characteristic for a macrocrystalline ZnSe sample. - Graphical abstract: Optical phonons in nanostructured thin films composed by zincblende zinc selenide quantum dots in strong size-quantization regime: competition between phonon confinement and strain-related effects. - Highlights: • Phonon confinement vs. strain-induced effects in ZnSe 3D QD assemblies were studied. • Shifts of the 1LO band result from an intricate compromise between the two effects. • SO and theoretically forbidden TO modes were accurately assigned. • Phonon relaxation time in as-deposited and annealed samples is 0.38 ps and 0.50 ps. • Both values are significantly smaller than in macrocrystalline ZnSe sample.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effect of Er{sup 3+} ions on the phase formation and properties of In{sub 2}O{sub 3}nanostructures crystallized upon microwave heating

Regular sized nanostructures of indium oxide (In{sub 2}O{sub 3}) were homogeneously grown using a facile route, i.e. a microwave-hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of Er{sup 3+} doping plays an important role in controlling the formation of cubic (bcc) and rhombohedral (rh) In{sub 2}O{sub 3} phases. The samples presented broad photoluminescent emission bands in the green-orange region, which were attributed to the recombination of electrons at oxygen vacancies. The photocatalytic activities of pure bcc-In{sub 2}O{sub 3} and a bcc-rh-In{sub 2}O{sub 3} mixture towards the UVA degradation of methylene blue (MB) were also evaluated. The results showed that Er{sup +3} doped In{sub 2}O{sub 3} exhibited the highest photocatalytic activity with a photonic efficiency three times higher than the pure oxide. The improved performance was attributed to the higher surface area, the greater concentration of electron traps due the presence of the dopant and the possible formation of heterojunctions between the cubic and rhombohedral phases. - Graphical abstract: Photodegradation curves as a function of irradiation time of the samples obtained upon rapid microwave heating. - Highlights: • Efficient and rapid microwave heating to obtain Er{sup 3+} doped In{sub 2}O{sub 3} nanostructures. • Er{sup 3+} ions doping is fundamental to stabilizing the crystalline rhombohedral phase. • Symmetry breaking induced by vacancies in the lattice leads to photoluminescence. • Surface area of doped sample was two times higher than the surface of pure oxide. • The presence of defects in the lattice structure favors photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Characterization of physicochemical properties of Pd/TiO{sub 2} nanostructured catalysts prepared by the photodeposition method

In this work, the sol–gel and hydrothermal methods were used to synthesize TiO{sub 2}-nanostructured supports. The palladium supported on sol–gel TiO{sub 2} and on hydrothermal-method-TiO{sub 2} nanotubes was obtained by incorporating it through photodeposition. The characterization was performed by X-ray diffraction, transmission electron microscopy, N{sub 2} physisorption, pulse chemisorption, ultraviolet–visible absorption spectroscopy and X-ray photoelectron spectroscopy. Both sol–gel-palladium–TiO{sub 2} and palladium-nanotube samples showed different palladium dispersion and physicochemical properties. In the palladium-nanotube sample, high surface area (243 m{sup 2}/g), H{sub 2}Ti{sub 3}O{sub 7} stable phase, and low band gap energy (2.35 eV) were obtained. Palladium-nanotubes and palladium-TiO{sub 2}, used as reference samples, were prepared by wet impregnation. - Highlights: • The precursors of TiO{sub 2} nanotubes were synthesized by the sol–gel method. • TiO{sub 2} nanostructures showed improved textural and morphological properties. • Pd nanoparticles around 1 nm were obtained by the photodeposition method. • TiO{sub 2}-nanotube-based catalysts can be a powerful tool for facing air pollution.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanostructures evolution assessment and spectroscopic properties modification induced by electronic energy loss in KTaO 3 crystal

Modifications of micro/nanostructure and photoelectric properties under swift ion irradiation (645 MeV Xe 35+ ) of KTaO 3 crystal with varying electronic energy losses (7.2–31.4 keV/nm) and ion velocities (0.18–5.00 MeV/u) have been studied by combining experimental and calculated approaches. The i-TS calculations combined with molecular dynamics simulations are compared with the experimental observations, revealing the inner track fine structures from individual spherical defects to continuous ion tracks with core–shell morphologies, and a quantitative relationship, including the melting (0.42 eV/atom), damage (0.75 eV/atom), and amorphous (1.71 eV/atom) thresholds, is established to successfully predict the inner disorder/amorphous proportions and track damage morphologies. The surface nanostructures of nanohillocks (isolated or partial overlaps) and nanopits (serious overlaps) directly depend on the combined action of the deposited potential and kinetic energies of incident ions, which induce local melting and sublimation in the near-surface region. Owing to the decreased recombination and the increased separation efficiency between electrons and holes, the higher photogenerated charge carrier mobility enhanced the photocurrent effect, further optimizing the photoconductivity performance in Xe 35+ -irradiated KTaO 3 . Therefore, controlled defect engineering using the ion irradiation technique, as an effective strategy, could design tailored nanostructure systems and regulate photoelectric properties, further promoting the development of novel technological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Topological structure enhanced nanostructure of high temperature polymer exhibiting more than ten times enhancement of dipolar response

Nanofillers in polymer composites will induce interface regions in the polymer with non-uniform nanostructures which can be approximated as multilayer shells surrounding nanofillers. This paper studies topological nanostructures in polymers that interface with one-dimensional (1-D) and zero-dimensional (0-D) nanofillers. This new class of dielectric polymer nanocomposites involves nanofillers at ultra-low volume loading (< 1 vol percent) that generate large dielectric enhancement. The results show that the dipolar response of polyetherimide, a high temperature dielectric polymer, is increased by more than ten times with ultra-low (0.75 vol %) loading of 1-D nanofillers. The results reveal that 1-D nanofillers induce cylindrical shell-topology in the polymer matrix which is more effective in enhancing the high dielectric constant interfacial region than the spherical shell-topology generated by 0-D fillers. Furthermore, the cylindrical shells generated by 1-D fillers provide much higher dielectric enhancement over a broader interfacial region in the polymer matrix, as compared to the spherical shells induced by 0-D nanofillers.

42 ENGINEERING↗
DOE OSTI2017

Characterization of Sulfur and Nanostructured Sulfur Battery Cathodes in Electron Microscopy Without Sublimation Artifacts

Abstract Lithium sulfur (Li–S) batteries have the potential to provide higher energy storage density at lower cost than conventional lithium ion batteries. A key challenge for Li–S batteries is the loss of sulfur to the electrolyte during cycling. This loss can be mitigated by sequestering the sulfur in nanostructured carbon–sulfur composites. The nanoscale characterization of the sulfur distribution within these complex nanostructured electrodes is normally performed by electron microscopy, but sulfur sublimates and redistributes in the high-vacuum conditions of conventional electron microscopes. The resulting sublimation artifacts render characterization of sulfur in conventional electron microscopes problematic and unreliable. Here, we demonstrate two techniques, cryogenic transmission electron microscopy (cryo-TEM) and scanning electron microscopy in air (airSEM), that enable the reliable characterization of sulfur across multiple length scales by suppressing sulfur sublimation. We use cryo-TEM and airSEM to examine carbon–sulfur composites synthesized for use as Li–S battery cathodes, noting several cases where the commonly employed sulfur melt infusion method is highly inefficient at infiltrating sulfur into porous carbon hosts.

25 ENERGY STORAGE↗
DOE OSTI2018

Direct Imaging of Low-Dimensional Nanostructures

Low-dimensional nanostructures are technologically desirable for their novel physical properties, as well as the benefits of packing density due to scale. In quantum computing, an ideal structure might consist of single dopant atoms precisely positioned a few nanometers below a surface [1]. There is also a need for truly atomic-scale interconnects and ancillary structures. However, due to their nanoscale dimensions, the physical properties of nanowires and related structures will depend on the environment in which they are embedded as well as their composition. This problem is particularly relevant for samples grown on ultra-clean surfaces, which may not survive outside of high-vacuum systems or which might be substantially affected by adatoms. The question then arises as to what happens to surface nanostructures or single dopant atoms during encapsulation or overgrowth.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Morphology-Driven Control of Metabolite Selectivity Using Nanostructure-Initiator Mass Spectrometry

Nanostructure-initiator mass spectrometry (NIMS) is a laser desorption/ionization analysis technique based on the vaporization of a nanostructure-trapped liquid "initiator" phase. Here in this work, we report an intriguing relationship between NIMS surface morphology and analyte selectivity. Scanning electron microscopy and spectroscopic ellipsometry were used to characterize the surface morphologies of a series of NIMS substrates generated by anodic electrochemical etching. Mass spectrometry imaging was applied to compare NIMS sensitivity of these various surfaces toward the analysis of diverse analytes. The porosity of NIMS surfaces was found to increase linearly with etching time where the pore size ranged from 4 to 12 nm with corresponding porosities estimated to be 7-70%. Surface morphology was found to significantly and selectively alter NIMS sensitivity. The small molecule (<2k Da) sensitivity was found to increase with increased porosity, whereas low porosity had the highest sensitivity for the largest molecules examined. Estimation of molecular sizes showed that this transition occurs when the pore size is <3× the maximum of molecular dimensions. While the origins of selectivity are unclear, increased signal from small molecules with increased surface area is consistent with a surface area restructuring-driven desorption/ionization process where signal intensity increases with porosity. In contrast, large molecules show highest signal for the low-porosity and small-pore-size surfaces. We attribute this to strong interactions between the initiator-coated pore structures and large molecules that hinder desorption/ionization by trapping large molecules. Lastly, this finding may enable us to design NIMS surfaces with increased specificity to molecules of interest.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Evaluation of Nanostructured β-Mn 2 V 2 O 7 Thin Films as Photoanodes for Photoelectrochemical Water Oxidation

β-Mn 2 V 2 O 7 (β-MVO) was recently reported to be a promising candidate for photoelectrochemical (PEC) water splitting, with a suitable band gap and band edge positions and reasonable stability and photoactivity in preliminary tests in alkaline solution. Here, we present an in-depth evaluation of the PEC performance and stability of phase-pure nanostructured β-Mn 2 V 2 O 7 films made by calcination of a spin-cast molecular ink. We show that β-Mn 2 V 2 O 7 dissolves in pure water, corrodes in aqueous electrolytes at pH 7 and 9, and converts to amorphous manganese (hydr)oxides within minutes at pH 13. Our β-Mn 2 V 2 O 7 films yielded only miniscule photocurrents (~uA cm -2 ) for the oxidation of iodide, sulfite, or water and the reduction of iodate or water in borate- and phosphate-buffered electrolytes at pH 7 and 9, the oxidation of [Fe(CN) 6 ] 4- or water at pH 13, and the oxidation of bromide in acetonitrile, regardless of film calcination temperature and time, film thickness, and illumination geometry. Minimal photoactivity was observed even in electrolytes in which film degradation was insignificant over the duration of the PEC tests. Ultrafast transient absorption spectroscopy shows that the poor photoactivity is likely the result of fast hole trapping and recombination at the MVO surface that leaves few free charge carriers beyond the picosecond time scale. Given its poor charge transport/extraction and chemical stability, native nanostructured β-Mn 2 V 2 O 7 is ineffective for solar water splitting and future research on this material should focus on the development of superior syntheses and film morphologies, MVO alloys, heterostructures, and surface coatings to alleviate recombination and boost operational stability. This work underscores the importance of careful follow-up studies of materials identified as "hits" in combinatorial materials discovery campaigns.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Nanostructured Metal Oxide Sorbents for the Collection and Recovery of Uranium from Seawater

The ability to collect uranium from seawater offers the potential for a long-term green fuel supply for nuclear energy. However, extraction of uranium, and other trace minerals, is challenging due to the high ionic strength and low mineral concentrations in seawater. Herein we evaluate the use of nanostructured metal oxide sorbents for the collection and recovery of uranium from seawater. Chemical affinity, chemical adsorption capacity and kinetics of preferred sorbent materials were evaluated. High surface area manganese and iron oxide nanomaterials showed excellent performance for uranium collection from seawater. Inexpensive nontoxic carbonate solutions were demonstrated to be an effective and environmental benign method of stripping the uranium from the metal oxide sorbents. Various formats for the utilization of the nanostructured metals oxide sorbent materials are discussed including traditional and nontraditional methods such as magnetic separation. Keywords: Uranium, nano, manganese, iron, sorbent, seawater, magnetic, separations, nuclear energy

Chouyyok, Wilaiwan↗
DOE OSTI2025

Nanopolysaccharide Builder: A User-Friendly Tool for Atomistic Models of Polysaccharide-Based Nanostructures

Here, we introduce Nanopolysaccharide Builder (NPB), a user-friendly software tool designed to construct polysaccharide nanostructures─mainly those based on cellulose, chitin, and chitosan─using experimental data or user-defined parameters. NPB enables the generation of cellulose and chitin allomorphs with customizable biochemical topologies and also facilitates the construction of large bundles that replicate nanostructures found in biological support systems, including plant cell walls and arthropod cuticles. The software outputs atomic Cartesian coordinates in Protein Data Bank (PDB) format and also provides atom connectivity files in PSF and PARM formats, ensuring seamless integration with major molecular dynamics (MD) engines such as NAMD, CHARMM, GROMACS, AMBER, OpenMM, and LAMMPS. Built on an interactive visualization framework, NPB features a graphical user interface (GUI) and supports both macOS and Linux operating systems. By enabling detailed atomic-scale studies of polysaccharide evolution in extracellular matrices and cell walls of algae, bacteria, fungi, and plants, NPB is poised to advance AI-guided research in sustainable chemical development and biomass utilization.

Wan, Zhangmin [Univ. of British Columbia, Vancouve↗
DOE OSTI2018

Anisotropic Ion Diffusion and Electrochemically Driven Transport in Nanostructured Block Copolymer Electrolytes

Nanostructured block copolymer electrolytes have the potential to enable solid-state batteries with lithium metal anodes. We present complete continuum characterization of ion transport in a lamellar polystyrene-b-poly(ethylene oxide) copolymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte as a function of salt concentration. Electrochemical measurements are used to determine the Stefan–Maxwell salt diffusion coefficients $^D_{+, 0}$, $^D_{-, 0}$, and $^D_{+, -}$. Individual self-diffusion coefficients of the lithium- and TFSI-containing species were measured by pulsed-field gradient NMR (PFG-NMR). The NMR data indicate that salt diffusion is locally anisotropic, and this enables determination of a diffusion coefficient parallel to the lamellae, D ∥ , and a diffusion coefficient through defects in the lamellae, D ⊥ . We quantify anisotropic diffusion by defining an NMR morphology factor and demonstrate that it is correlated to defect density seen by transmission electron microscopy. We find agreement between the electrochemically determined Stefan–Maxwell diffusion coefficients and the diffusion coefficient D⊥ determined by PFG-NMR. Our work indicates that the performance of nanostructured block copolymer electrolytes in batteries is strongly influenced by ion transport through defects.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Transient Studies of CO 2 Adsorption over CeO 2 Nanostructures with In Situ DRIFTS and Modulation Excitation

Experiments of in-situ DRIFTS combined with modulation excitation (ME) spectroscopy showed a rich surface chemistry associated with the adsorption of CO 2 on nanocubes and nanospheres of ceria. The nanocubes exposed faces with a (100) orientation, with the edges and corners displaying (110) and (111) orientations, respectively. Here, the nanospheres mainly contained ceria (111) and (110) planes. DFT calculations showed that CO 2 is a multidentate adsorbate on ceria that can undergo changes in its bonding configuration depending on the chemical environment. At 250 °C, a temperature typically used for the conversion of CO 2 into oxygenates, alkanes and olefins, CO 2 reacted with O centers or OH groups present on the nanocubes and nanospheres to yield bi- and tri-dentate carbonates, hydroxycarbonates, and formates. Both nanostructures were highly reactive and a dynamic equilibrium was established: carbonate species were rapidly generated upon the injection of CO 2 and they decomposed upon the removal of CO 2 from the gas phase. In the case of the ceria nanocubes, the adsorption/desorption processes were essentially reversible, opening the door to catalytic transformations. A larger concentration of defects in the ceria nanospheres led to strongly bound carbonates and formates that may be spectators, site blockers, or surface modifiers in catalytic processes. In the ME studies, additional intermediates were detected, and it was clear that the response of surface species to the presence/absence of CO 2 was highly dependent on the morphology of the ceria nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Ab Initio -Based Bond Order Potential to Investigate Low Thermal Conductivity of Stanene Nanostructures

We introduce a bond order potential (BOP) for stanene based on an ab initio derived training data set. The potential is optimized to accurately describe the energetics, as well as thermal and mechanical properties of a free-standing sheet, and used to study diverse nanostructures of stanene, including tubes and ribbons. As a representative case study, using the potential, we perform molecular dynamics simulations to study stanene’s structure and temperature-dependent thermal conductivity. We find that the structure of stanene is highly rippled, far in excess of other 2-D materials (e.g., graphene), owing to its low in-plane stiffness (stanene: ~ 25 N/m; graphene: ~ 480 N/ m). The extent of stanene’s rippling also shows stronger temperature dependence compared to that in graphene. Furthermore, we find that stanene based nanostructures have significantly lower thermal conductivity compared to graphene based structures owing to their softness (i.e., low phonon group velocities) and high anharmonic response. Our newly developed BOP will facilitate the exploration of stanene based low dimensional heterostructures for thermoelectric and thermal management applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Electrochemical Growth of Copper Hydroxy Double Salt Films and Their Conversion to Nanostructured p-Type CuO Photocathodes

New electrochemical synthesis methods were developed to produce copper hydroxy double salts (Cu-HDS) films with four different intercalated anions (NO 3 - , SO 4 2- , Cl - , and dodecyl sulfate (DS)) as pure crystalline films as-deposited (Cu 2 NO 3 (OH) 3 , Cu 4 SO 4 (OH) 6 , Cu 2 Cl(OH) 2 , and Cu 2 DS(OH) 3 ). These methods are based on p-benzoquinone reduction, which increases the local pH at the working electrode and triggers the precipitation of Cu 2+ and appropriate anions as Cu-HDS films on the working electrode. The resulting Cu-HDS films could be converted to crystalline Cu(OH) 2 and CuO films by immersing them in basic solutions. Since Cu-HDS films were composed of 2D crystals due to the atomic level layered structure of HDS, the CuO films prepared from Cu-HDS films have unique low dimensional nanostructures, creating high surface areas, which cannot be obtained by direct deposition of CuO that has a 3D atomic level crystal structure. Here, the resulting nanostructures allowed the CuO films to facilitate electron-hole separation and demonstrate great promise for photocurrent generation when investigated as a photocathode for a water splitting photoelectrochemical cell. Electrochemical synthesis of Cu-HDS films and their facile conversion to CuO films will provide new routes to tune morphologies and properties of the CuO electrodes that may not be possible by other synthesis means.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Kinetically Controlled Formation of Semi-crystalline Conjugated Polymer Nanostructures

Conjugated polymer (CP) materials that are considered as an attractive choice for various electronic and optoelectronic applications possess highly heterogeneous complex structures that can span several orders of magnitude in length scale. This is due to the intricate coupling effects of weak secondary interactions and entropic forces that determine molecular organization in bulk polymer materials. Understanding the influence of molecular interactions on the emergence and evolution of nano- and microscale structures is of paramount importance to the guided design and development of condensed CP materials. Such understanding is even more critical for the rational design of hierarchical systems away from equilibrium, where weak molecular interactions can guide the system along competing kinetic pathways toward local energy minima and metastable architectures. In this work, we studied a promising concept for accessing various kinetically stabilized semi-crystalline CP nanostructures that are formed in the process of controlled chain-growth Kumada catalyst-transfer polymerization initiated by a small-molecule catalytic species which can exist in equilibrium between free and aggregated states. Specifically, we chose a small-molecule perylenedicarboximide (PDCI) polymerization catalytic initiator which has a strong tendency toward reversible supramolecular assembly–disassembly that can be controlled by temperature. Addition of a thiophene monomer to a solution of the PDCI initiator starts the chain-growth polymerization process, which produces distinct nanoscale semi-crystalline polythiophene structures formed under predominant kinetic control. Furthermore, we demonstrated that, depending on the reaction temperature (which affects the fine balance between the position of PDCI assembly–disassembly equilibrium, rate of polymerization, and solvent–solute interactions for the growing polythiophene chains), a range of kinetically trapped hierarchically organized semi-crystalline CP systems with substantially varying optoelectronic properties could be obtained. In addition to spectroscopic and electron microscopic studies, in order to better reveal the structural aspects of the generated polymer nanoscale systems, we carried out a series of X-ray diffraction and neutron scattering experiments which indicated complex hierarchical organization in these kinetically stabilized CP assembled materials. We expect that this in situ polymerization-based approach can lead to a general way to expand access to various semi-crystalline CP nanostructured materials with broadly tunable electronic and optical properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Electrostatic Interactions Control the Nanostructure of Conjugated Polyelectrolyte–Polymeric Ionic Liquid Blends

Polyelectrolyte complexation offers unique opportunities to compatibilize polymers with very different backbone chemistries and to control the morphology of the resulting blend via electrostatic manipulation. In this study, we demonstrate the ability to formulate homogeneous complexes of a conjugated polyelectrolyte with a polymeric ionic liquid, utilizing the electrostatic attraction among their oppositely charged side chains. Variation of electrostatic parameters, such as counterion concentration or polymer charge fraction, tunes the morphology of these polymer complexes from homogeneously disordered blend to weakly structured microemulsion where the local ordering arises from backbone-immiscibility-induced microphase segregation. Our experimental observations are in qualitative agreement with both field-theoretic simulation and random-phase approximation calculations. Simulated morphology snapshots suggest and experimental evidence also indicates that the microphase-segregated complex likely takes on a cocontinuous microemulsion structure. Our findings show that ionic interactions are an effective pathway to compatibilize polymers at macroscopic length scales while achieving controlled nanostructures in these ionic blends. Such systems have great potential for engineering the nanostructure of polymers to tailor applications such as nanofiltration, catalysis, and energy storage, where local ordering can enhance the physical properties of an otherwise macroscopically homogeneous structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

High Efficiency Si Photocathode Protected by Multifunctional GaN Nanostructures

Photoelectrochemical water splitting is a clean and environmentally friendly method for solar hydrogen generation. Its practical application, however, has been limited by the poor stability of semiconductor photoelectrodes. In this work, we demonstrate the use of GaN nanostructures as a multifunctional protection layer for an otherwise unstable, low-performance photocathode. The direct integration of GaN nanostructures on n + -p Si wafer not only protects Si surface from corrosion but also significantly reduces the charge carrier transfer resistance at the semiconductor/liquid junction, leading to long-term stability (>100 h) at a large current density (>35 mA/cm 2 ) under 1 sun illumination. The measured applied bias photon-to-current efficiency of 10.5% is among the highest values ever reported for a Si photocathode. Here given that both Si and GaN are already widely produced in industry, our studies offer a viable path for achieving high-efficiency and highly stable semiconductor photoelectrodes for solar water splitting with proven manufacturability and scalability.

36 MATERIALS SCIENCE↗