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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Partially reduced Ru/RuO 2 composites as efficient and pH-universal electrocatalysts for hydrogen evolution

Efficient and long-term stable electrocatalysts for the hydrogen evolution reaction (HER) via water splitting are urgently desired to ease the energy crisis and develop the sustainability of human society. However, the HER performance of state-of-the-art Pt in non-acidic solutions is unsatisfactory due to the severely sluggish kinetics. In this work, DFT theoretical calculations reveal that the Ru/RuO 2 composites enable high HER activity to be pursued under non-acidic conditions because of the distinctive Ru and RuO 2 interface, which possess not only a strong capability to adsorb and dissociate water but also appropriate binding energies of H and OH. Therefore, we employ a simple strategy, including heating under an oxygen-poor environment and/or in situ electrochemical reduction, to partially reduce RuO 2 . The formed Ru/RuO 2 interfaces demonstrate superior HER activities (e.g. η 10 = 17 mV, 35 mV dec –1 in 1 M KOH) than Pt/C (e.g. η 10 = 27 mV, 58 mV dec –1 in 1 M KOH) at both small (10–100 mA cm –2 ) and large (1 A cm –2 ) current densities in alkaline solution and even real seawater. Comprehensive experiments were conducted to investigate the structure-HER performance relationships. Moreover, benefiting from the bifunctional character of RuO2, a two-electrode system based on Ru/RuO 2 composites and RuO 2 exhibits the lowest cell voltage for water splitting in both 1 M KOH and 0.5 M H 2 SO 4 , respectively. A 300 h-stability test at 10 mA cm –2 without an obvious decay demonstrates the industrial prospects of the Ru/RuO 2 composites to generate green energy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Insights into the Reactivity of Brookite TiO 2 Nanorods in Liquid Water from Ab Initio Molecular Dynamics Simulations

Brookite TiO 2 , a rare natural polymorph of TiO 2 , has been reported to be an excellent photocatalyst for the production of hydrogen from water and aqueous alcohol solutions, especially when it is reduced and synthesized in the form of nanorods. Here, we investigate the reactivity of stoichiometric and reduced brookite nanorods in liquid water using ab initio molecular dynamics and hybrid density functional theory calculations. Our simulations show a much higher water dissociation fraction on reduced nanorods than on stoichiometric ones, with an accumulation of the resulting bridging hydroxyls (O br H) and terminal hydroxyls (Ti –OH) on different facets of the nanorod. ObrH groups accumulate preferentially on low-energy (210) facets, where they are stabilized by adjacent reduced Ti (Ti 3+ ) sites, while Ti –OH groups prefer to form at the four-fold coordinated Ti atoms on high-energy (010) facets. This hydroxylation pattern also favors the spatial localization of excited holes on the (010) facets. This coupling between water-induced surface chemistry and charge separation underpins the enhanced photocatalytic activity of brookite nanorods, providing useful information for the design of more efficient TiO2-based nanostructures for solar-driven hydrogen evolution.

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

Isotope effects in dynamics of water isotopologues induced by core ionization at an x-ray free-electron laser

Dynamical response of water exposed to x-rays is of utmost importance in a wealth of science areas. We exposed isolated water isotopologues to short x-ray pulses from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we identify significant structural dynamics with characteristic isotope effects in H 2 O 2+ , D 2 O 2+ , and HDO 2+ , such as asymmetric bond elongation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. A method to disentangle the sequences of events taking place upon the consecutive absorption of two x-ray photons is described. The obtained deep look into structural properties and dynamics of dissociating water isotopologues provides essential insights into the underlying mechanisms.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of ‘Ni(OH) 2 -clothed Pt-tetrapods’ with an amorphous Ni(OH) 2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH) 2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. Furthermore, the markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effect of Ambient Organic Acids on the Water Structure at ${\rm TiO}_{2}$ Interfaces

A molecular-level understanding of the effects of ambient organic compounds on the wettability of titanium dioxide ( ${\rm TiO}_{2}$ ) surfaces is relevant to many of its energy-related and environmental applications. Herein, we focus on two common atmospheric carboxylic acids, formic and acetic acid, and characterize their adsorption/ desorption at the aqueous interfaces of anatase and rutile ${\rm TiO}_{2}$ using molecular dynamics with an ab initio deep neural network potential. Our simulations show that these acids prefer to be localized in the interfacial water layers close to the ${\rm TiO}_{2}$ surface where they are stabilized by the interaction/exchange of their acid proton with a surface oxygen, rather than chemisorb at the surface Ti sites by displacing the adsorbed water. Notably, these acids make the surface of anatase hydrophobic, whereas the larger fraction of adsorbed water dissociation can offset their effect on rutile. Furthermore, these results provide a picture where carboxylic acids control the wettability of ${\rm TiO}_{2}$ largely through acid-base chemistry at the interface rather than chemisorption on the oxide surface, a finding that can help improve the design of self-cleaning surfaces and photocatalytic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Trace levels of PtRu on NiMo foam electrodes towards hydrogen evolution reaction

Electrochemical water splitting plays a critical role in high purity hydrogen production. To lower capital cost and energy consumption, efficient catalysts are required to boost the hydrogen evolution reaction (HER), especially in alkaline media. Although PtRu alloy materials are still considered the state-of-the-art catalyst for the HER under alkaline media, large-scale application is hindered by its scarcity and high cost. NiMo alloy catalysts can be potential Pt-free alternatives to drive the sluggish kinetics of the HER under alkaline media, but their HER activity is still not ideal due to the limitation of Volmer step. Herein, we investigated the impact of trace levels of PtRu catalysts on NiMo electrodes towards the HER by incorporating advantages of both PtRu and NiMo catalysts to minimize cost and maintain a promising HER activity. Trace levels of PtRu catalysts from 0.0173 to 0.2648 mg cm −2 were loaded on commercial NiMo foam electrodes by a facile electrodeposition technique utilizing ppm concentration levels of PtRu in electrolyte. The results show that 0.0173 mg cm −2 PtRu loading on NiMo electrode can significantly enhance HER activity compared to the pristine NiMo foam electrode (Tafel slopes drop from ∼170 to ∼60 mV dec −1 ) due to the remarkable decline of energy barriers towards water dissociation and hydrogen adsorption. Meanwhile, the rate determining step (RDS) switches from the Volmer step to the Heyrovsky step when the PtRu loading increases to 0.0675 mg cm −2 . Promising catalytic stability is observed at 100 mA cm −2 over the course of 50 h with a PtRu loading of 0.1198 mg cm −2 . In conclusion, this work demonstrates a potential strategy to decrease the cost and simultaneously maintain superior HER performance by integrating trace levels of PtRu catalyst with NiMo foam electrodes.

Electrochemical water splitting↗
DOE OSTI2024

Construction of a Pt‐CeO x Interface for the Electrocatalytic Hydrogen Evolution Reaction

Abstract The creation of metal‐metal oxide interfaces is an important approach to fine‐tuning catalyst properties through strong interfacial interactions. This article presents the work on developing interfaces between Pt and CeO x that improve Pt surface energetics for the hydrogen evolution reaction (HER) within an alkaline electrolyte. The Pt‐CeO x interfaces are formed by depositing size‐controlled Pt nanoparticles onto a carbon support already coated with ultrathin CeO x nanosheets. This interface structure facilitates substantial electron transfer from Pt to CeO x , resulting in decreased hydrogen binding energies on Pt surfaces, and water dissociation for the HER, as predicted by the density functional theory (DFT) calculations. Electrochemical testing indicates that both Pt specific activity and mass activity are improved by a factor of 2 to 3 following the formation of Pt‐CeO x interfaces. This study underscores the significance and potential of harnessing robust interfacial effects to enhance electrocatalytic reactions.

25 ENERGY STORAGE↗
DOE OSTI2025

Robust Oxygen‐Vacancy‐Engineered Co(OH) 2 /Cu Heterostructures Boost Nitrate Electroreduction to Ammonia beyond 2 A cm −2

Electrocatalytic nitrate reduction reaction (NO 3 RR) presents a sustainable paradigm for green NH 3 synthesis and NO 3 − wastewater valorization. However, overcoming sluggish NO 3 RR kinetics under industrial-current operation persists as a critical challenge. Herein, robust oxygen vacancy-enriched heterostructures (O v -Co(OH) 2 /Cu) are engineered through in situ electrochemical reconstruction. By coupling Cu-mediated NO 3 − -to-NO 2 − conversion with O v -Co(OH) 2 -accelerated NO 2 − -to-NH 3 transformation, this heterostructured system delivers an unprecedented NH 3 yield rate of 167.8 mg h −1 cm −2 and 97.7% Faradaic efficiency at >2 A cm −2 , while maintaining exceptional current tolerance over 25 h. Operando spectroscopic characterizations and theoretical calculations reveal that the introduction of O v in Co(OH) 2 synergistically accelerates water dissociation to ensure continuous hydrogen supply and optimizes *NOOH adsorption, reducing the energy barrier for the rate-limiting step (*NO 2 to *NOOH). To demonstrate practical viability, a membrane-electrode-assembly electrolyzer integrating NO 3 RR with glycerol oxidation reaction achieves highly effective co-production of NH 3 and formate alongside wastewater treatment. In conclusion, this work offers new insights into the rational design of electrocatalysts through in situ reconstruction-induced vacancy engineering for scalable and practical NO 3 RR applications.

ammonia synthesis↗
DOE OSTI2026

Combining ToF‐SIMS and Multivariate Analysis to Resolve Active Sites on Ni‐Based HER Catalysts

Unambiguous identification of active sites in heterogeneous catalysis remains a major challenge, particularly for materials with ultrathin, chemically mixed surface layers. Here, we demonstrate a generalizable approach that combines time-of-flight secondary ion mass spectrometry (ToF-SIMS) with multivariate statistical analysis (principal component analysis [PCA] and multivariate curve resolution [MCR]) to resolve catalytically relevant motifs at the nanoscale. Using Ni electrodes as a model system, PCA distinguished hydroxide-enriched domains from oxide- and metal-rich regions, while MCR decomposed depth profiles and 3D images into hydroxide, oxide, and metallic layers with nanometer resolution. A unique secondary-ion fragment, NiO 3 H 3 − (m/z 108.94), emerged as a marker of hydroxide-rich environments and correlated with hydrogen evolution reaction (HER) activity across a series of Ni electrodes. Complementary density functional theory (DFT) calculations revealed that Ni(OH) 2 clusters adjacent to metallic Ni offer the most favorable water dissociation energetics, establishing the structural origin of the marker. While illustrated here for Ni-based HER, this workflow provides a broadly applicable framework to isolate and rank near-surface patterns that govern catalytic activity, thereby extending ToF-SIMS from a qualitative probe to a predictive tool for active site identification.

HER active sites↗
DOE OSTI2026

Electronegativity-Guided Site Differentiation in High-Entropy Alloy for pH-universal Hydrogen Evolution Reactions

Enhancing the intrinsic activity of transition metal catalysts for the hydrogen evolution reaction (HER) remains a critical challenge in sustainable energy conversion. Herein, we report an electronegativity-guided site differentiation strategy in a single-phase CoNiCuMoW high-entropy alloy (HEA) via electrodeposition by incorporating high-electronegativity 4d/5d orbital transition metals (Mo, W) into the face-centered cubic (fcc) matrix (CoNiCu). The as-synthesized HEA demonstrates exceptional HER performance in all pH conditions, delivering an outstanding overpotential of 65 mV (alkaline), 28 mV (acidic), and 155 mV (neutral) at a current density of 100 mA cm−2, showing performance comparable to commercial Pt/C and has excellent long-term stability at high current density (1 A cm−2, 1000 h). X-Ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations reveal that the incorporation of Mo/W simultaneously alters the local coordination environment and induces element-dependent charge redistribution, accompanied by a system-level d-band center downshift, thereby optimizing the hydrogen binding strength across multimetallic sites. Meanwhile, oxophilic Mo/W sites lower the water dissociation energy barrier. These synergistic effects collectively enable efficient and durable pH-universal HER performance.

Wu, Yutong↗
DOE OSTI2024

Unlocking High Capacity and Reversible Alkaline Iron Redox Using Silicate-Sodium Hydroxide Hybrid Electrolytes

Alkaline iron (Fe) batteries are attractive due to the high abundance, low cost, and multiple valent states of Fe but show limited columbic efficiency and storage capacity when forming electrochemically inert Fe 3 O 4 on discharging and parasitic H 2 on charging. Herein, sodium silicate is found to promote Fe(OH) 2 /FeOOH against Fe(OH) 2 /Fe 3 O 4 conversions. Electrochemical experiments, operando X-ray characterization, and atomistic simulations reveal that improved Fe(OH) 2 /FeOOH conversion originates from (i) strong interaction between sodium silicate and iron oxide and (ii) silicate-induced strengthening of hydrogen-bond networks in electrolytes that inhibits water transport. Furthermore, the silicate additive suppresses hydrogen evolution by impairing energetics of water dissociation and hydroxyl de-sorption on iron surfaces. In conclusion, this new silicate-assisted redox chemistry mitigates H 2 and Fe 3 O 4 formation, improving storage capacity (199 mAh g -1 in half-cells) and coulombic efficiency (94 % after 400 full-cell cycles), paving a path to realizing green battery systems built from earth-abundant materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

P‐Doping Modulated RuIr Nanoparticles Anchored on Co/N/C Catalysts with Improved Alkaline Hydrogen Evolution Activity and Stability

Achieving efficient and stable hydrogen evolution reactions in alkaline conditions is crucial for hydrogen production. In this study, a RuIr/Co (SA) NC-P catalyst featuring RuIr alloys alongside P-doping and CoNx sites is developed. RuIr alloying optimizes the electronic structure between Ru and Ir, promoting electron transfer from Ru to Ir. P-doping further modulates the electronic properties of RuIr alloys, optimizing hydrogen binding energy and weakening Ru─OH binding energy, facilitating rapid H 2 generation and OH ad transfer. Meanwhile, CoNx promotes water dissociation, providing a fast proton delivery path for RuIr alloys. The catalyst exhibits enhanced HER activity with a low overpotential of 20 mV at 10 mA cm −2 , a Tafel slope of 20.4 mV dec −1 , and a turnover frequency of 19.5 H 2 s −1 at 150 mV overpotential. Moreover, catalyst stability is improved 8 times by mitigating RuIr alloy dissolution/agglomeration via P-doping. In conclusion, this work introduces a promising approach for developing efficient and stable HER electrocatalysts.

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

Affinity for OH – Produces Four-Coordinated Zn 2+ Impurities in Hydrated Amorphous Calcium Carbonate

Using ab initio based molecular dynamics and electronic structure calculations, we show that Zn impurities in hydrated amorphous calcium carbonate (ACC) have a much lower coordination number than other divalent impurities due to covalent interactions between the 3d Zn shell and the oxygen atoms of the carbonate and water groups. Further, the local structure around Zn in ACC, including the predicted low coordination number, is confirmed by X-ray absorption spectroscopy of synthetic Zn-bearing ACC. The strong Zn–O chemical interaction leads to substantial water dissociation and slightly disrupts the hydrogen bonding network. Implications of Zn 2+ incorporation for ACC stability are discussed.

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

Fullerene Promotes CO 2 Reduction to Methanol by a Cobalt(II) Phthalocyanine Electrocatalyst

Heterogenization of molecular electrocatalysts offers an attractive way to improve the catalytic selectivity and efficiency of CO 2 conversion to liquid fuels. Herein, we employ density functional theory to compare the mechanism of CO 2 RR by a cobalt(II) tetra(amino)phthalocyanine (Co(II)Pc(NH 2 ) 4 ) electrocatalyst with and without the presence of fullerene support. Our DFT calculations suggest that the CO 2 reduction mechanism is initiated by a metal-based electron reduction followed by subsequent CO 2 nucleophilic addition, electron transfer, proton transfer, water dissociation, and proton-coupled electron transfer steps that lead to CO and methanol formation. We show that graphitic interactions between the Co(II)Pc(NH 2 ) 4 electrocatalyst and C 60 support selectively improve the CO 2 RR to methanol at mild potentials. The undesirable hydrogen evolution reaction (HER) was also investigated for both electrocatalysts and proceeds via the protonation of the cobalt metal center over the nitrogen atom in the inner ring. The competition between the HER and the CO 2 RR was improved in favor of CO and methanol formation using the Co(II)Pc(NH 2 ) 4 @C 60 electrocatalyst. Overall, our results suggest C 60 as a promising graphitic support for molecular electrocatalysts integration for CO 2 catalysis.

Alcohols↗
DOE OSTI2026

Intrinsically Conductive {pi}‑d Conjugated Layers with Co–N4 Active Sites for Efficient Nitrate Electrocatalysis and Zinc-Nitrate Batteries

Electrochemical synthesis of ammonia from nitrate has been extensively investigated as a potential alternative to the energy-intensive Haber-Bosch process. This approach not only operates under ambient conditions but also simultaneously removes nitrate contaminants while producing ammonia as a value-added product. However, the ongoing quest lies in designing an efficient electrocatalyst that achieves a high ammonia yield rate, high selectivity, and long-term stability. Herein, we report the outstanding performance of a Co–N4 coordinated π-d layered Co3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) in nitrate electrocatalysis. The unique combination of abundant Co–N4 active sites and superior electrical conductivity enables significant electrocatalytic activity, delivering a maximum ammonia yield rate of 56.8 mg cm–2 h–1 at −0.8 V vs RHE and a Faradaic efficiency of ∼91% at −0.4 V vs RHE. Mechanistic analysis reveals that alkaline conditions accelerate water dissociation to generate adsorbed hydrogen intermediates (H*), which are utilized by Co–N4 sites to drive the stepwise hydrogenation of nitrate to ammonia while suppressing competing hydrogen evolution reaction (HER) pathways. Furthermore, integration of this catalyst into a zinc-nitrate battery resulted in a maximum power density of 5.3 mW cm–2 and an open-circuit potential of ∼1.45 V. These results highlight the potential of π-d conjugated Co–N4 materials as an efficient catalyst for both environmental remediation and energy conversion.

Namvar, shahrirar↗
DOE OSTI2026

Measuring pH Changes Inside a Bipolar Membrane Junction

Here, the local pH environment within bipolar membrane (BPM) junctions is complex and not well understood, yet it is important to control for advancing the performance of BPM-based electrochemical systems. We report a voltammetric strategy using an ultrathin Ni mesh pH probe to spatially resolve pH changes in the BPM junction during model BPM electrolyzer operation. Under reverse bias, we observe depletion of OH – at the anion-exchange layer (AEL) interface, with a degree diminishing with increasing distance from the AEL. These gradients correlate with current-dependent water dissociation (WD) and are modulated by the electric field and the surface charge state of the catalyst. By correlating spatial pH profiles with the surface-charging behavior of WD catalysts, we explore a mechanism of catalyst-mediated H + and OH – transfer facilitated by hydrogen-bonding networks. These findings highlight the role of local chemistry and electrostatics in BPM performance and offer new methods to probe and engineer catalytic junctions in electrochemical energy devices.

Hou, Shujin [University of California, Berkeley, C↗
DOE OSTI2019

Hydroxide promotes carbon dioxide electroreduction to ethanol on copper via tuning of adsorbed hydrogen

Producing liquid fuels such as ethanol from CO 2 , H 2 O, and renewable electricity offers a route to store sustainable energy. The search for efficient electrocatalysts for the CO 2 reduction reaction relies on tuning the adsorption strength of carbonaceous intermediates. Here, we report a complementary approach in which we utilize hydroxide and oxide doping of a catalyst surface to tune the adsorbed hydrogen on Cu. Density functional theory studies indicate that this doping accelerates water dissociation and changes the hydrogen adsorption energy on Cu. We synthesize and investigate a suite of metal-hydroxide-interface-doped-Cu catalysts, and find that the most efficient, Ce(OH) x -doped-Cu, exhibits an ethanol Faradaic efficiency of 43% and a partial current density of 128 mA cm -2 . Mechanistic studies, wherein we combine investigation of hydrogen evolution performance with the results of operando Raman spectroscopy, show that adsorbed hydrogen hydrogenates surface *HCCOH, a key intermediate whose fate determines branching to ethanol versus ethylene.

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

General synthesis of high-entropy single-atom nanocages for electrosynthesis of ammonia from nitrate

Given the growing emphasis on energy efficiency, environmental sustainability, and agricultural demand, there’s a pressing need for decentralized and scalable ammonia production. Converting nitrate ions electrochemically, which are commonly found in industrial wastewater and polluted groundwater, into ammonia offers a viable approach for both wastewater treatment and ammonia production yet limited by low producibility and scalability. Here we report a versatile and scalable solution-phase synthesis of high-entropy single-atom nanocages (HESA NCs) in which Fe and other five metals-Co, Cu, Zn, Cd, and In-are isolated via cyano-bridges and coordinated with C and N, respectively. Incorporating and isolating the five metals into the matrix of Fe resulted in Fe-C5 active sites with a minimized symmetry of lattice as well as facilitated water dissociation and thus hydrogenation process. As a result, the Fe-HESA NCs exhibited a high selectivity toward NH3 from the electrocatalytic reduction of nitrate with a Faradaic efficiency of 93.4% while maintaining a high yield rate of 81.4 m h -1 mg -1 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗