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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Energy coupling and stoichiometry of Zn 2+ /H + antiport by the prokaryotic cation diffusion facilitator YiiP

YiiP from Shewanella oneidensis is a prokaryotic Zn 2+ /H + antiporter that serves as a model for the Cation Diffusion Facilitator (CDF) superfamily, members of which are generally responsible for homeostasis of transition metal ions. Previous studies of YiiP as well as related CDF transporters have established a homodimeric architecture and the presence of three distinct Zn 2+ binding sites named A, B, and C. In this study, we use cryo-EM, microscale thermophoresis and molecular dynamics simulations to address the structural and functional roles of individual sites as well as the interplay between Zn 2+ binding and protonation. Structural studies indicate that site C in the cytoplasmic domain is primarily responsible for stabilizing the dimer and that site B at the cytoplasmic membrane surface controls the structural transition from an inward facing conformation to an occluded conformation. Binding data show that intramembrane site A, which is directly responsible for transport, has a dramatic pH dependence consistent with coupling to the proton motive force. A comprehensive thermodynamic model encompassing Zn 2+ binding and protonation states of individual residues indicates a transport stoichiometry of 1 Zn 2+ to 2–3 H + depending on the external pH. This stoichiometry would be favorable in a physiological context, allowing the cell to use the proton gradient as well as the membrane potential to drive the export of Zn 2+ .

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Predicting Outcomes of Nanoparticle Attachment by Connecting Atomistic, Interfacial, Particle, and Aggregate Scales

Predicting nanoparticle aggregation and attachment phenomena requires a rigorous understanding of the interplay among crystal structure, particle morphology, surface chemistry, solution conditions, and interparticle forces, yet no comprehensive picture exists. We used an integrated suite of experimental, theoretical, and simulation methods to resolve the effect of solution pH on the aggregation of boehmite nanoplatelets, a case study with important implications for the environmental management of legacy nuclear waste. Real-time observations showed that the particles attach preferentially along the (010) planes at pH 8.5 and the (101) planes at pH 11. To rationalize these results, we established the connection between key physicochemical phenomena across the relevant length scales. Starting from molecular-scale simulations of surface hydroxyl reactivity, we developed an interfacial-scale model of the corresponding electrostatic potentials, with subsequent particle-scale calculations of the resulting driving forces allowing successful prediction of the attachment modes. Finally, we scaled these phenomena to understand the collective structure at the aggregate-scale . Here, our results indicate that facet-specific differences in surface chemistry produce heterogeneous surface charge distributions that are coupled to particle anisotropy and shape-dependent hydrodynamic forces, to play a key role in controlling aggregation behavior.

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

Etching-Chemistry-Driven Ruthenium Doping on Ti 3 C 2 T x MXene for Optimizing Electrochemical Performance

We demonstrate that the etching chemistry used during MXene synthesis from Ti 3 AlC 2 MAX phase significantly influences surface functionalization and structural vacancies, which in turn affect ruthenium (Ru) ion interactions. Using hydrofluoric acid (HF) and ammonium bifluoride (NH 4 HF 2 ) as etchants, we obtained MXene surfaces with distinct functional groups and Ti vacancies that impact Ru ion interactions and electrochemical performance. Both MXene variants (labeled MX(H) and MX(N), respectively) exhibited negative zeta potentials in their pristine state, but upon the addition of Ru the zeta potential for MX(H) reached 12.9 mV while that for MX(N) remained negative at −6.4 mV. This adsorption resulted in a 14.4-fold increase in the specific capacitance of MX(H)/Ru compared to pristine MX(H), whereas MX(N)/Ru exhibited only a 4.4-fold increase over its pristine counterpart. X-ray diffraction analysis identified the formation of ammonium titanium oxide fluoride, (NH 4 ) 3 TiOF 5 , on MX(N), which likely contributed to its reduced Ru adsorption. X-ray photoelectron spectroscopy suggested the presence of Ti vacancies in both MXene variants; however, their behavior toward Ru accommodation differed markedly, with MX(H) showing the most obvious shift in the Ti 2p peak in the XPS survey spectrum, while MX(N) showed the most obvious shift in the C 1s peak. Electron paramagnetic resonance spectroscopy further demonstrated a distinct alteration in the spectral signatures of MX(H) upon Ru addition, in contrast to the negligible changes in MX(N), indicating effective passivation of the Ti defect sites in MX(H) via vacancy-assisted Ru doping. Cyclic voltammetry showed that Ru-incorporated MX(H) nanocomposites exhibit more efficient redox-active sites, as reflected in their higher capacitance values. These findings highlight the pivotal role of MXene surface chemistry in controlling cation adsorption, providing valuable insights for the rational design of high-performance electrodes.

2D surface engineering↗
DOE OSTI2025

Chemically Enhanced Electrodialysis (CEED) for Recovery of Rare Earth Elements

Rare-earth elements are crucial for numerous technologically relevant industries including energy, electronics, and aerospace; however, both the supply and separation of rare earths are pressing challenges. The long-term goal of the collaborative project is to develop a novel approach to existing extraction behaviors. To achieve this goal, a class of electrodialysis membranes with novel ion-gating functionality will be developed and paired with a conventional electrodialysis strategy. The hypothesis of the work is that incorporating sequestrants of suitable structures at the surface of the electrodialysis membrane will enhance extraction efficiency for ions of interest. Our ability to prepare sequestrants of diverse conformations and to adapt their molecular structure for binding lanthanides renders the proposed technology a versatile method for selective ion separation. Our approach will enable an entirely new technological approach to the separation of valuable rare-earth elements.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The NO reduction by CO over NiO x /CeO 2 catalysts with a fixed Ni surface density: pretreatment effects on the catalyst structure and catalytic activity

NiO x /CeO 2 catalysts have shown promising results in various catalytic reactions, including the NO reduction by CO. Here, in this study, we investigated the effect of oxidation and reduction treatments on the NO reduction by CO over pretreated NiO x /CeO 2 catalysts. A series of oxidized and reduced supported NiO x catalysts were synthesized in two steps: (1) the pretreatment of CeO 2 supports at different temperatures (400, 500, and 700 °C) under oxidizing and reducing conditions and (2) the synthesis of NiO x /CeO 2 catalysts by an incipient wetness impregnation method (IWI) with a fixed surface density of 5.3 Ni per nm 2 under specific conditions (oxidation/reduction) applied during the CeO 2 treatment. The prepared catalysts were characterized via BET, ICP/OES, Raman, XPS, and XRD to understand their physicochemical properties. The results showed that as the pretreatment temperature increased, the physicochemical properties of NiO x /CeO 2 catalysts were changed: a decreased specific surface area (SSA), decreased oxygen vacancy/defect sites, and an increased crystallite size. The oxidized NiO x /CeO 2 catalyst at a lower pretreatment temperature displayed a better catalytic activity, indicating that the physicochemical properties of the catalysts were key factors in enhancing the catalytic activity. To understand the intermediate species and reaction mechanism during the NO reduction by CO, an in situ DRIFTS study was performed and a possible reaction mechanism was also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Fiber-optic sensor packaging assessment and benchmarking for embedded sensing applications

Fiber optic-based sensing for non-destructive evaluation (NDE) and structural health monitoring of various infrastructure and energy assets is an increasingly important sensing scheme. Because of their immunity to electromagnetic interferences, versatility in sensing mechanisms and designs as well as capability for distributed sensing, the fiber optic sensing is of great interest for embedding within infrastructures using advanced manufacturing methods. However, the protection of fiber optic sensors during advanced manufacturing-based embedding is an important aspect for infrastructure monitoring in practice. While successful installation of fiber optic sensors has been accomplished through application of epoxy or adhesives on infrastructure surfaces, there has been only limited investigation of fiber protection packaging schemes which are compatible with in-situ repair techniques such as the metallic cold-spray. With increasing interest and importance of cold spray-based repair processes, the integration of fiber optic sensors simultaneously during the repair is equally important. In this work, we focus our efforts on investigating various types of packaging schemes for their compatibility and integrability on the surfaces of metallic structures such as oil and gas pipelines during an in-situ repair coating. First, we consider sandblasting using silica sand particles of various size for optical fibers on the surface of a metallic coupon as a useful proxy test of sensor packaging stability. Structural damage of packaging is characterized by means of optical microscopy and the optical integrity of embedded fiber optic cables is examined using optical backscatter reflectometry (OBR). In addition, initial investigation of metallic cold-spray embedded fiber optic cables under various packaging on metallic substrates is also considered with early conclusions and future directions.

Fiber-optic sensors, Sensors packaging, Metallic C↗
DOE OSTI2026

Modulation induced by very-large-scale motions on the inclination angle of wall-attached eddies: an atmospheric surface layer experiment

The forward leaning inclination angle, 𝛾, of coherent turbulent structures is a well-known feature of wall-bounded turbulent flows. Although invariant across friction Reynolds numbers within the range 𝑅𝑒 𝜏 =10 3 −10 6 , 𝛾 can vary significantly across turbulent scales within a high-Reynolds-number flow. Very-large-scale motions (VLSMs) are known to induce significant changes in the instantaneous shear profile, which is a conditioning event that could trigger variability in the inclination angle of smaller coherent turbulent structures. Although this aspect has been extensively studied via numerical and laboratory experiments, few studies have explored this feature for a very-high-Reynolds-number atmospheric flow. In this work, the inclination angle of turbulent structures within the atmospheric surface layer at a very high Reynolds number (𝑅𝑒 𝜏 =7.9 ×10 5 ) is investigated by deploying a scanning Doppler light detection and ranging and a super large particle image velocimetry (SLPIV) apparatus. The inclination angle of wall-attached eddies is inferred either from the two-point correlation of streamwise velocity (𝛾 =41.1∘) or with a scale-dependent approach through the spectral linear stochastic estimator (SLSE). The SLSE (and, thus, the scale-dependent inclination angle) is conditionally evaluated based on the high- and low-momentum events induced by VLSMs, both in the streamwise (𝑢′𝑉𝐿𝑆𝑀) and in the vertical (𝑤′ 𝑉𝐿𝑆𝑀) velocity components. As a result, lower inclination angles (𝛾 =30° −50°) are found for 𝑢$^{'}_{VLSM}$ >0 (𝑤$^{'}_{VLSM}$ <0), while higher values (50° −85°) are ascribed to 𝑢$^{'}_{VLSM}$ <0 (𝑤$^{'}_{VLSM}$ >0). This result emphasises the primary role that VLSMs play in shaping the wall-attached eddy geometry, which, in turn, is crucial to determine the Reynolds stress balance within the wall-attached eddy range.

42 ENGINEERING↗
DOE OSTI2022

Exsolution-Driven Surface Transformation in the Host Oxide

Exsolution synthesizes self-assembled metal nanoparticle catalysts via phase precipitation. An overlooked aspect in this method thus far is how exsolution affects the host oxide surface chemistry and structure. Such information is critical as the oxide itself can also contribute to the overall catalytic activity. Here, combining X-ray and electron probes, we investigated the surface transformation of thin-film SrTi 0.65 Fe 0.35 O 3 during Fe 0 exsolution. We found that exsolution generates a highly Fe-deficient near-surface layer of about 2 nm thick. Moreover, the originally single-crystalline oxide near-surface region became partially polycrystalline after exsolution. Such drastic transformations at the surface of the oxide are important because the exsolution-induced nonstoichiometry and grain boundaries can alter the oxide ion transport and oxygen exchange kinetics and, hence, the catalytic activity toward water splitting or hydrogen oxidation reactions. These findings highlight the need to consider the exsolved oxide surface, in addition to the metal nanoparticles, in designing the exsolved nanocatalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Self-Assembly of Anisotropic Particles on Curved Surfaces

The surface curvature of membranes, interfaces, and substrates plays a crucial role in shaping the self-assembly of particles adsorbed on these surfaces. However, little is known about the interplay between particle anisotropy and surface curvature and how they couple to alter the free energy landscape of particle assemblies. Using molecular dynamics simulations, we investigate the effect of prescribed curvatures on a quasi-2D assembly of anisotropic patchy particles. By varying curvature and surface coverage, we uncover a rich geometric phase diagram, with curvature inducing ordered structures entirely absent on planar surfaces. Large spatial domains of ordered structures can contain hidden microdomains of orientational textures imprinted by the surface on the assembly. The dynamical landscape is also reshaped by surface curvature, with a glass-like state emerging at modest densities and high curvature. Changes to the symmetry of the surface curvature are found to result in distinct structures, including phases with mesoscale ordering. In conclusion, our findings show that the coupling between surface curvature and particle geometry opens an unexplored space of morphologies and structures that can be exploited for material design.

Fluids↗
DOE OSTI2021

Post-remediation geophysical assessment: Investigating long-term electrical geophysical signatures resulting from bioremediation at a chlorinated solvent contaminated site

There is a growing need to assess long-term impacts of active remediation strategies on treated aquifers. A variety of biogeochemical alterations can result from interactions of the amendment with the aquifer, conceivably leading to a geophysical footprint of the long-term alteration of an aquifer. This concept of post-remediation geophysical assessment was investigated in a shallow, chlorinated solvent-contaminated aquifer six to eight years after amendment delivery. Surface resistivity imaging and cross-borehole resistivity and induced polarization (IP) imaging were performed on a transect that spanned treated and untreated zones of the aquifer. Established relationships between IP parameters and surface electrical conductivity were used to predict vertical profiles of electrolytic conductivity and surface conductivity from the inverted cross-borehole images. Aqueous geochemistry data, along with natural gamma and magnetic susceptibility logs, were used to constrain the interpretation. The electrical conductivity structure determined from surface and borehole imaging was foremost controlled by the electrolytic conductivity of the interconnected pore space, being linearly related to fluid specific conductance. The electrolytic conductivity (and thus the conductivity images alone) did not discriminate between treated and untreated zones of the aquifer. In contrast, inverted phase angles and surface conductivities did discriminate between treated and untreated zones of the aquifer, with the treated zone being up to an order of magnitude more polarizable in places. Supporting aqueous chemistry and borehole logging datasets indicate that this geophysical footprint of the long-term impact of the remediation on the aquifer is most likely associated with the formation of polarizable, dispersed iron sulfide minerals. The study opens the door to the possibility of employing time-lapse electrical geophysical measurements to assist with long-term environmental stewardship of legacy sites undergoing active remediation.

bioremediation↗
DOE OSTI2022

The role of coverage effects on the structure–sensitivity of formic acid electrooxidation on Pd surfaces

Direct formic acid (FA) fuel cells (DFAFCs) with Pd anode catalysts are promising for small portable applications. During the electrooxidation of formic acid (FAO), CO accumulates on the Pd electrocatalyst, thereby decreasing its performance. In this work, we use density functional theory (DFT; RPBE) to elucidate the significance of coverage effects on the structure–sensitivity of FAO over four low–index Pd surfaces: Pd(1 1 1), Pd(1 0 0), Pd(1 1 0), and Pd(2 1 1). We construct coverage–dependent Gibbs free energy diagrams and in agreement with experiment, predict that Pd(1 0 0) and Pd(2 1 1) are the most active surfaces. Additionally, we find that the presence of CO spectator species can alter the preferred electrooxidation pathway under different applied potentials. Furthermore, such pathway transitions appear to be critical for rationalizing experimental trends regarding electrocatalytic activity and are only captured when coverage effects are accounted for. Insights derived from this work may facilitate the design of improved FAO electrocatalysts.

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

Solution Chemistry to Control Boron-Containing Monolayers on Silicon: Reactions of Boric Acid and 4-Fluorophenylboronic Acid with H- and Cl-terminated Si(100)

In this work, the reactions of boric acid and 4-fluorophenylboronic acid with H- and Cl-terminated Si(100) surfaces in solution were investigated. X-ray photoelectron spectroscopy (XPS) studies reveal that both molecules react preferentially with Cl–Si(100) and not with H–Si(100) at identical conditions. On Cl–Si(100), the reactions introduce boron onto the surface, forming a Si–O–B structure. The quantification of boron surface coverage demonstrates that the 4-fluorophenylboronic acid leads to ~2.8 times higher boron coverage compared to that of boric acid on Cl–Si(100). Consistent with these observations, density functional theory studies show that the reaction of boric acid and 4-fluorophenylboronic acid is more favorable with the Cl- versus H-terminated surface and that on Cl–Si(100) the reaction with 4-fluorophenylboronic acid is ~55.3 kJ/mol more thermodynamically favorable than the reaction with boric acid. The computational studies were also used to demonstrate the propensity of the overall approach to form high-coverage monolayers on these surfaces, with implications for selective-area boron-based monolayer doping.

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

CH 4 Activation over Perovskite Catalysts: True Density and Reactivity of Active Sites

The high thermal stability of perovskites has drawn attention toward their applications for catalytic CH 4 activation and conversion, typically occurring at high temperatures. The reaction rates of perovskite catalysts for CH 4 combustion, however, trail behind those of noble metal catalysts. Ways to optimize the performance of perovskite catalysts are destined to trial-and-error approaches unless their complex reconstructed surfaces are correlated with fundamental kinetic parameters. Discerning the intrinsic activity of surface catalytic sites and the density of those sites is crucial to rationally envision complex metal oxides with enhanced catalytic performance. Here, the present work presents a detailed kinetic analysis of catalytic CH 4 combustion over a set of seven perovskites (SrTiO 3 , SrZrO 3 , SrFeO 3 , LaFeO 3 , LaInO 3 , LaCoO 3 , LaMnO 3 ) with various surface terminations. Steady-state isotopic transient kinetic analysis was employed to measure turnover frequency (TOF) and density of surface intermediates (N) under operando conditions. Top surface characterization elucidated performance-structure relationships between near-monolayer surface composition and intrinsic reactivity of the catalysts. By using a chemical etching procedure to expose Fe-sites at the top surface of LaFeO 3 (LaFeO 3 , HNO 3 ), its TOF was increased 4-fold, compared with the unmodified sample, although N on the surface of LaFeO 3 , HNO 3 decreased. Density functional theory simulations corroborated that surface Fe-termination and La-Fe termination offer lower energetic barriers for CH 4 activation when compared with La-termination. In general, surface reconstruction is shown as a tool to tune TOF and N to improve reaction rates. This work fills a gap in current kinetic studies of perovskites through a careful assessment and discussion of the density and intrinsic reactivity of active sites for methane combustion over well-characterized reconstructed perovskite surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Diffractive optical computing in free space

Abstract Structured optical materials create new computing paradigms using photons, with transformative impact on various fields, including machine learning, computer vision, imaging, telecommunications, and sensing. This Perspective sheds light on the potential of free-space optical systems based on engineered surfaces for advancing optical computing. Manipulating light in unprecedented ways, emerging structured surfaces enable all-optical implementation of various mathematical functions and machine learning tasks. Diffractive networks, in particular, bring deep-learning principles into the design and operation of free-space optical systems to create new functionalities. Metasurfaces consisting of deeply subwavelength units are achieving exotic optical responses that provide independent control over different properties of light and can bring major advances in computational throughput and data-transfer bandwidth of free-space optical processors. Unlike integrated photonics-based optoelectronic systems that demand preprocessed inputs, free-space optical processors have direct access to all the optical degrees of freedom that carry information about an input scene/object without needing digital recovery or preprocessing of information. To realize the full potential of free-space optical computing architectures, diffractive surfaces and metasurfaces need to advance symbiotically and co-evolve in their designs, 3D fabrication/integration, cascadability, and computing accuracy to serve the needs of next-generation machine vision, computational imaging, mathematical computing, and telecommunication technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Genomic discovery of an evolutionarily programmed modality for small-molecule targeting of an intractable protein surface

The vast majority of intracellular protein targets are refractory toward small-molecule therapeutic engagement, and additional therapeutic modalities are needed to overcome this deficiency. Here, the identification and characterization of a natural product, WDB002, reveals a therapeutic modality that dramatically expands the currently accepted limits of druggability. WDB002, in complex with the FK506-binding protein (FKBP12), potently and selectively binds the human centrosomal protein 250 (CEP250), resulting in disruption of CEP250 function in cells. The recognition mode is unprecedented in that the targeted domain of CEP250 is a coiled coil and is topologically featureless, embodying both a structural motif and surface topology previously considered on the extreme limits of “undruggability” for an intracellular target. Structural studies reveal extensive protein–WDB002 and protein–protein contacts, with the latter being distinct from those seen in FKBP12 ternary complexes formed by FK506 and rapamycin. Outward-facing structural changes in a bound small molecule can thus reprogram FKBP12 to engage diverse, otherwise “undruggable” targets. The flat-targeting modality demonstrated here has the potential to expand the druggable target range of small-molecule therapeutics. As CEP250 was recently found to be an interaction partner with the Nsp13 protein of the SARS-CoV-2 virus that causes COVID-19 disease, it is possible that WDB002 or an analog may exert useful antiviral activity through its ability to form high-affinity ternary complexes containing CEP250 and FKBP12.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Porous mesh manifold for enhanced boiling performance

High-performance electronics are continuously demanding cooling of higher heat fluxes. Phase-change cooling, including pool boiling, is a useful approach to address this challenge; however, competition between liquid and vapor flows generally limit the heat fluxes that can be dissipated. A range of strategies to control these flows have been investigated previously, including capillary guides. Here a manifold structure formed from a metallic mesh is investigated to control the disposition of liquid and vapor phases above a pool fed boiling surface enhanced with porous structures. Copper mesh forms defined liquid flow paths, using capillary action to guide and distribute liquid evenly over the heated surface, along with open channels to facilitate vapor escape. The mesh provides a novel structure for liquid guidance that imposes low resistance to liquid flow while occluding a minimal area of heated surface underneath. The manifold performance is characterized in boiling fed by a pool of water above a laser-textured aluminum nitride heat dissipation surface with pin–fin structures having heights of 110 µm and spacing of 30 µm with a heated area of 5 mm x 5 mm. A maximum heat flux of 490 W/cm 2 is reached with the manifold in the pool fed configuration, representing an increase of more than 65% over the porous pin fin surface alone. The maximum stable superheat observed for the manifold of 36K is 14K higher than that for the porous surface without the manifold. The factors limiting performance of the manifold are analyzed. High superheat is attributed to partial flooding of the boiling surface as suggested by the reduction in superheat using external suction. Similar systems and structures for enhanced two-phase cooling are compared.

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

Actuation via surface chemistry induced surface stress

A method of controlling macroscopic strain of a porous structure includes contacting a porous structure with a modifying agent which chemically adsorbs to a surface of the porous structure and modifies an existing surface stress of the porous structure. Additional methods and systems are also presented.

Biener, Juergen↗
DOE OSTI2020

Constructing an Adaptive Heterojunction as a Highly Active Catalyst for the Oxygen Evolution Reaction

Electrochemical water splitting is of prime importance to green energy technology. Particularly, the reaction at the anode side, namely the oxygen evolution reaction (OER), requires a high overpotential associated with O—O bond formation, which dominates the energy-efficiency of the whole process. Activating the anionic redox chemistry of oxygen in metal oxides, which involves the formation of superoxo/peroxo-like (O 2 ) n – , commonly occurs in most highly active catalysts during the OER process. Here, a highly active catalyst is designed: electrochemically delithiated LiNiO 2 , which facilitates the formation of superoxo/peroxo-like (O 2 ) n – species, i.e., NiOO*, for enhancing OER activity. The OER-induced surface reconstruction builds an adaptive heterojunction, where NiOOH grows on delithiated LiNiO 2 (delithiated-LiNiO 2 /NiOOH). At this junction, the lithium vacancies within the delithiated LiNiO 2 optimize the electronic structure of the surface NiOOH to form stable NiOO* species, which enables better OER activity. This finding provides new insight for designing highly active catalysts with stable superoxo-like/peroxo-like (O 2 ) n – for water oxidation.

36 MATERIALS SCIENCE↗