Dilute Metal Research Articles

Dilute Pd−Ni Alloy through Low‐temperature Pyrolysis for Enhanced Electrocatalytic Hydrogen Oxidation

AbstractDesigning highly active and cost‐effective electrocatalysts for the alkaline hydrogen oxidation reaction (HOR) is critical for advancing anion‐exchange membrane fuel cells (AEMFCs). While dilute metal alloys have demonstrated substantial potential in enhancing alkaline HOR performance, there has been limited exploration in terms of rational design, controllable synthesis, and mechanism study. Herein, we developed a series of dilute Pd−Ni alloys, denoted as x% Pd−Ni, based on a trace‐Pd decorated Ni‐based coordination polymer through a facile low‐temperature pyrolysis approach. The x% Pd−Ni alloys exhibit efficient electrocatalytic activity for HOR in alkaline media. Notably, the optimal 0.5 % Pd−Ni catalyst demonstrates high intrinsic activity with an exchange current density of 0.055 mA cm−2, surpassing that of many other alkaline HOR catalysts. The mechanism study reveals that the strong synergy between Pd single atoms (SAs)/Pd dimer and Ni substrate can modulate the binding strength of proton (H)/hydroxyl (OH), thereby significantly reducing the activation energy barrier of a decisive reaction step. This work offers new insights into designing advanced dilute metal or single‐atom‐alloys (SAAs) for alkaline HOR and potentially other energy conversion processes.

Anomalous Frequency and Temperature Dependent Scattering in the Dilute Metallic Phase in Lightly Doped SrTiO_{3}.

The mechanism of superconductivity in materials with aborted ferroelectricity and its emergence out of a dilute metallic phase in systems like doped SrTiO_{3} is an outstanding issue in condensed matter physics. This dilute metal has anomalous properties that are both similar and different to those found in the normal state of other unconventional superconductors. For instance, T^{2} resistivity can be found at densities that are too small to allow current decay through electron-electron scattering. We have investigated the optical properties of the dilute metallic phase in doped SrTiO_{3} using THz time-domain spectroscopy. At low frequencies the THz response exhibits a Drude-like form as expected for typical metal-like conductivity. We observed the frequency and temperature dependencies to the low energy scattering rate Γ(ω,T)∝(ℏω)^{2}+(pπk_{B}T)^{2} expected in a conventional Fermi liquid. However, we find the lowest known p values of 0.39-0.72. As p is 2 in a canonical Fermi liquid and existing models based on energy dependent elastic scattering bound p from below to 1, our observation lies outside current explanation. Our data also give insight into the high temperature regime and show that the temperature dependence of the resistivity derives in part from strong T dependent mass renormalizations.

Dilute Pd-Ni Alloy through Low-temperature Pyrolysis for Enhanced Electrocatalytic Hydrogen Oxidation.

Designing highly active and cost-effective electrocatalysts for the alkaline hydrogen oxidation reaction (HOR) is critical for advancing anion-exchange membrane fuel cells (AEMFCs). While dilute metal alloys have demonstrated substantial potential in enhancing alkaline HOR performance, there has been limited exploration in terms of rational design, controllable synthesis, and mechanism study. Herein, we developed a series of dilute Pd-Ni alloys, denoted as x% Pd-Ni, based on a trace-Pd decorated Ni-based coordination polymer through a facile low-temperature pyrolysis approach. The x% Pd-Ni alloys exhibit efficient electrocatalytic activity for HOR in alkaline media. Notably, the optimal 0.5% Pd-Ni catalyst demonstrates high intrinsic activity with an exchange current density of 0.055 mA cm-2, surpassing that of many other alkaline HOR catalysts. The mechanism study reveals that the strong synergy between Pd single atoms (SAs)/Pd dimer and Ni substrate can modulate the binding strength of proton (H)/hydroxyl (OH), thereby significantly reducing the activation energy barrier of a decisive reaction step. This work offers new insights into designing advanced dilute metal or single-atom-alloys (SAAs) for alkaline HOR and potentially other energy conversion processes.

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels.

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li+ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li+ . The channels attract and enrich Li+ ions by up to orders of magnitude. As a result, our material sieves Li+ out of various common ions such as Na+ , K+ , Ca2+ , Mg2+ and Al3+ . Moreover, by spontaneously enriching Li+ ions, it realizes an effective Li+ /Na+ selectivity of 1422 in artificial seawater where the Li+ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels

AbstractBiological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom‐sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li+ selectivity. The pillared channels and crown ether have an angstrom‐scale size. The crown ether specifically allows the low‐barrier transport of Li+. The channels attract and enrich Li+ ions by up to orders of magnitude. As a result, our material sieves Li+ out of various common ions such as Na+, K+, Ca2+, Mg2+ and Al3+. Moreover, by spontaneously enriching Li+ ions, it realizes an effective Li+/Na+ selectivity of 1422 in artificial seawater where the Li+ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.

Green mining of mining water using surface e-precipitation

Surface e-precipitation (SEP) is a largely unknown in separation electrochemical technique that uniquely combines the kinetic advantage of chemical precipitation with the advantages of conventional surface-based separation techniques such as electrodeposition/electrowinning (e-deposition), electrosorption, and adsorption. This work explores the potential of SEP in recovering valuable elements and removing toxic elements from mining water of a polysulfide ore origin. Without employing any reagent, in a simple batch-type laboratory setup with a carbon electrode, SEP alone or in combination with e-deposition can concentrate groups of dilute (20–30 mg/L) and ultradilute (<2 mg/L) valuable metals such as Zn, Al, Cu, Co, Ni, and rare earth elements (REE) vs gangue metals such as Mn, Fe, and an excess of Ca and Mg by an order of magnitude at highly competitive rate and energy consumption values which can reach 0.25 m3/(kg carbon ⋅ min) and 0.02 kWh/m3, respectively. The recovery and relative content of the concentrated metals can be controlled by the method design and operational variables such as applied potential, retention time (water treatment rate), and the number of stages. The uptake of Zn and Cu by SEP and e-deposition, respectively, is compared in mining waters and synthetic sulfate solutions. This comparison reveals that the ionic matrix of mining water promotes SEP but inhibits e-deposition. The comparison with the chemical precipitation at similar pH and reaction time shows that SEP has higher selectivity but lower recovery. These results demonstrate that SEP is a promising novel approach to valorizing and decontaminating acid mine drainage (AMD), process water, and metal-loaded wastewater.

Effect of Metal Chloride Impurities on Equilibrium Potential of Fe/FeCl2 in Eutectic LiCl-KCl

Abstract In this study, interaction of dilute metal chloride solutes in molten eutectic LiCl-KCl was studied via equilibrium potential measurements. Open circuit potential (OCP) was measured between a pure iron rod and a Ag/AgCl reference electrode with concentration of FeCl2 varying from 0.2-1 mol% at 530oC. The Nernst equation was used to calculate activity coefficient of FeCl2 based on OCP. Measurements were made in LiCl-KCl-FeCl2 with and without additions of 0.5 mol% CsCl, NaCl, and LaCl3. The activity coefficient of FeCl2 was found to be unaffected by these small concentrations of CsCl, LaCl3, and NaCl. However, there was observed evidence that the activity coefficient of FeCl2, above 0.8 mol% Fe, may be affected by the presence of LaCl3 at higher concentrations beginning around 0.5 mol% La. Over the full range of conditions tested, the activity coefficient of FeCl2 in molten LiCl-KCl ranged from 2.95x10-5 to 1.01x10-4.

T-Square Dependence of the Electronic Thermal Resistivity of Metallic Strontium Titanate.

The temperature dependence of the phase space for electron-electron (e-e) collisions leads to a T-square contribution to electrical resistivity of metals. Umklapp scattering is identified as the origin of momentum loss due to e-e scattering in dense metals. However, in dilute metals like lightly doped strontium titanate, the origin of T-square electrical resistivity in the absence of umklapp events is yet to be pinned down. Here, by separating electron and phonon contributions to heat transport, we extract the electronic thermal resistivity in niobium-doped strontium titanate and show that it also displays a T-square temperature dependence. Its amplitude correlates with the T-square electrical resistivity. The Wiedemann-Franz law strictly holds in the zero-temperature limit, but not at finite temperature, because the two T-square prefactors are different by a factor of ≈3, like in other Fermi liquids. Recalling the case of ^{3}He, we argue that T-square thermal resistivity does not require umklapp events. The approximate recovery of the Wiedemann-Franz law in the presence of disorder would account for a T-square electrical resistivity without umklapp.

Divalent Metal Cation Optical Sensing Using Single-Walled Carbon Nanotube Corona Phase Molecular Recognition.

Colloidal single-walled carbon nanotubes (SWCNTs) offer a promising platform for the nanoscale engineering of molecular recognition. Optical sensors have been recently designed through the modification of noncovalent corona phases (CPs) of SWCNTs through a phenomenon known as corona phase molecular recognition (CoPhMoRe). In CoPhMoRe constructs, DNA CPs are of great interest due to the breadth of the design space and our ability to control these molecules with sequence specificity at scale. Utilizing these constructs for metal ion sensing is a natural extension of this technology due to DNA's well-known coordination chemistry. Additionally, understanding metal ion interactions of these constructs allows for improved sensor design for use in complex aqueous environments. In this work, we study the interactions between a panel of 9 dilute divalent metal cations and 35 DNA CPs under the most controlled experimental conditions for SWCNT optical sensing to date. We found that best practices for the study of colloidal SWCNT analyte responses involve mitigating the effects of ionic strength, dilution kinetics, laser power, and analyte response kinetics. We also discover that SWCNT with DNA CPs generally offers two unique sensing states at pH 6 and 8. The combined set of sensors in this work allowed for the differentiation of Hg2+, Pb2+, Cr2+, and Mn2+. Finally, we implemented Hg2+ sensing in the context of portable detection within fish tissue extract, demonstrating nanomolar level detection.

Phonon drag thermal Hall effect in metallic strontium titanate

SrTiO3, a quantum paralectric, displays a detectable phonon thermal Hall effect (THE). Here, we show that the amplitude of the THE is extremely sensitive to stoichiometry. It drastically decreases upon substitution of a tiny fraction of Sr atoms with Ca, which stabilizes the ferroelectric order. It drastically increases by an even lower density of oxygen vacancies, which turn the system to a dilute metal. The enhancement in the metallic state exceeds by far the sum of the electronic and the phononic contributions. We explain this observation as an outcome of three features: 1) Heat is mostly transported by phonons; 2) the electronic Hall angle is extremely large; and 3) there is substantial momentum exchange between electrons and phonons. Starting from Herring's picture of phonon drag, we arrive to a quantitative account of the enhanced THE. Thus, phonon drag, hitherto detected as an amplifier of thermoelectric coefficients, can generate a purely thermal transverse response in a dilute metal with a large Hall angle. Our results reveal a hitherto-unknown consequence of momentum-conserving collisions between electrons and phonons.

Superconductivity from energy fluctuations in dilute quantum critical polar metals

Superconductivity in low carrier density metals challenges the conventional electron-phonon theory due to the absence of retardation required to overcome Coulomb repulsion. Here we demonstrate that pairing mediated by energy fluctuations, ubiquitously present close to continuous phase transitions, occurs in dilute quantum critical polar metals and results in a dome-like dependence of the superconducting Tc on carrier density, characteristic of non-BCS superconductors. In quantum critical polar metals, the Coulomb repulsion is heavily screened, while the critical transverse optical phonons decouple from the electron charge. In the resulting vacuum, long-range attractive interactions emerge from the energy fluctuations of the critical phonons, resembling the gravitational interactions of a chargeless dark matter universe. Our estimates show that this mechanism may explain the critical temperatures observed in doped SrTiO3. We provide predictions for the enhancement of superconductivity near polar quantum criticality in two- and three-dimensional materials that can be used to test our theory.

Understanding and Modifying the Scaling Relations for Ammonia Synthesis on Dilute Metal Alloys: From Single-Atom Alloys to Dimer Alloys

Understanding and Modifying the Scaling Relations for Ammonia Synthesis on Dilute Metal Alloys: From Single-Atom Alloys to Dimer Alloys

Sr2+ and Ba2+ salts induced conformational structure of sodium polyacrylate PAA investigated by molecular dynamics simulations

The shrinkage of sodium-poly(acrylate) PAA in divalent salt (strontium chloride (SrCl2) and barium chloride (BaCl2) solutions is investigated by atomistic molecular dynamics (MD) simulations to study the salt effect on PAA structure. The salt concentration (Cs) was varied in the range of 0 < Cs < 1 M for fully charged PAA. The PAA radius-of-gyration (Rg) decreases with Cs in the presence of both the divalent salts in qualitative agreement with experiments. The PAA chain stiffness calculated in persistence length (Lp) decreases over the entire range of Cs. At lower Cs, the PAA chains don't form aggregate, while at higher salt concentrations, PAA chains undergo self-association in both the divalent salts. The PAA-Water H-bonds decreases with Cs significantly in the presence of BaCl2 as compared to SrCl2. The PAA-Na+ radial distribution function (RDF) shows a decrease in its coordination number with Cs. The distribution of salt-ions around PAA shows that the Ba2+ condensation onto PAA is more significant than Sr2+ because of a greater coordination number for the former than the latter. Overall, the present study significantly advanced the molecular-level understanding of PAA microstructure in the dilute divalent metal salt solution.

Correlation governs the impurity (Ti, Zr, Hf) diffusion in face−centered cubic iridium through first−principles calculation

Solid state diffusion depends on many factors, including crystal structure, vacancy concentration, energy barrier, jump frequency, correlation, etc.. In this work, those factors were systematically investigated for dilute IVB transition metals X (X = Ti, Zr, Hf) diffusion in face−centered cubic (FCC) Ir using first−principles calculations together with quasi−harmonic thermodynamics, climb−image nudged elastic band (CINEB), and five−frequency diffusion model. The results show that correlation which is often neglected in low melting point metals and alloys plays a key role in the impurity diffusion in Ir. The correlation factor which ranges from 10−13 at 500 K to 10−1 at 2000 K overturns the contributions from other factors, like vacancy concentration, energy barrier, and jump frequency. The diffusion coefficient of Ir−X (X = Ti, Zr, Hf) systems follows DHf > DZr > DTi, different from our traditional knowledge. Our findings not only give a good recount to the counterintuitive experimental phenomena in Ir oxidation resistance coating or ultrahigh−temperature Ir-based superalloys, but also provide valuable diffusion data for rational design of Ir-based materials for applications with harsh environment.

Insights about inductively coupled plasma optical emission spectroscopy interferences of major rare earth elements in complex e-waste feeds

The advent of rare earth elements (REEs) with optoelectronic properties has shifted the technology paradigm from digital to a smart and hybrid world. Their substantial uses also resulted in a large piling up of e-waste. Therefore, e-waste is now a lucrative recycling target for the recovery of such critical raw materials. Their recycling from e-waste is often challenged by dilute metal concentration, complex composition, and difficult chemical characterisation. Generally, the characterisation of e-waste involves elemental determination techniques, such as inductively coupled plasma optical emission spectroscopy (ICP-OES) or inductively coupled plasma mass spectrometry (ICP-MS). ICP-OES is attractive for a recycling or research sector because it has a higher matrix tolerance and lower cost than ICP-MS. In this work, the intensity at 445 line positions measured by an ICP-OES instrument was compiled in a 2D diagram to map interferences by 27 prominent lines from 9 REEs. The second diagram shows the impact at 230 neighbouring line positions measured in each of, in total, 17 (i.e., 9 REEs and 8 non-REEs) single-standard solutions in terms of the concentration of the element type affected. The spectral interference correction algorithm proposed here had been developed by us for a recycling process to obtain pure Y, Eu, and Tb from fluorescent powder (FP) in spent lamps. The ICP-OES analysis and spectral interference correction approach presented here can be applied to any element and e-waste type. To underline this, the paper gives examples for elements in dissolved FP and surrogate NdFeB magnet samples.

On the Origin and the Amplitude of T‐Square Resistivity in Fermi Liquids

AbstractIn 1937, Baber, Landau, and Pomeranchuk postulated that collisions between electrons generates a contribution to the electric resistivity of metals with a distinct T2 temperature dependence. The amplitude of this term is small in common metals, but dominant in metals hosting either heavy carriers or a low concentration of them. The temperature dependence is set by the size of the scattering phase, but the microscopic source of dissipation is not straightforward. To explain how electron–electron collisions lead to momentum leak, Umklapp events or multiple electron reservoirs have been invoked. This interpretation is challenged by several experimental observations: the persistence of T‐square resistivity in dilute metals (in which the two mechanisms are irrelevant), the successful extension of Kadowaki–Woods scaling to dilute metals, and the observation of a size‐dependent T‐square thermal resistivity () and its WiedemannFranz correlation with T‐square electrical resistivity. This paper argues that much insight is provided by the case of normal liquid 3He where the T‐square temperature dependence of energy and momentum diffusivity is driven by fermionfermion collisions. The amplitude of T‐square resistivity in 3He and in metals share a common scaling. Thus, the ubiquitous T‐square electrical resistivity ultimately stems from the Fermi‐liquid temperature dependence of momentum diffusivity.

Convective heat transfer estimation of dilute metal oxide nanofluids in VUV surface tuned minichannel using Mach-Zehnder interferometry

• Minichannels were surface tuned with 30 min of Vacuum Ultraviolet irradiation. • Test fluids used were dilute concentrations of alumina and silica nanofluids and Deionized water. • Mach-Zehnder interferometry was utilized to extract heat transfer data from the minichannels. • Effect of surface tuning was visible only at low Reynolds Number. • At high Reynolds number, the advective effects became more significant. • Higher concentration of alumina nanofluid showed better heat transfer rates under all flow conditions. Convective heat transfer performances of dilute metal oxide suspensions in D.I water (Deionized water) flowing through a VUV (Vacuum Ultraviolet) surface tuned mini channel with a hydraulic diameter of 3 mm were quantified in this work. The experiment was carried out first on a channel with untreated PDMS coating with a contact angle of 86.2 ± 2.7° and then with a VUV treated PDMS channel having a contact angle of 2.7 ± 2.1°. Mach-Zehnder interferometry, a non-intrusive measurement technique, was employed to conduct fringe analysis in the test channel. Modified Naylor – Duarte method was used to quantify the heat transfer coefficients in the minichannels. Experiments conducted using alumina and silica nanofluids were compared with D.I water in both channels. The experiments were carried out at three different heat inputs (5 W, 10 W, and 15 W) and three other Reynolds numbers (294, 591, and 855). At Re = 294 and 5 W of heat input, the highest volume fraction of alumina nanofluid in VUV treated minichannel recorded a 5.92 ± 1.9% increment in heat transfer rates compared to the same charge in untreated minichannel. For the same flow conditions in VUV treated minichannels, 0.02 vol% alumina nanofluid recorded a 20.11 ± 3.4% increment in heat transfer rates than D.I water, while it was 6.11 ± 2.7% for 0.02 vol% of silica nanofluids. In the VUV treated minichannel at 5 W and Re = 294, the boundary layer thickness showed a reduction of 9.64 ± 1.6% for 0.02 vol% alumina nanofluid, as compared to the untreated channel. But at Re = 855, the percentage enhancement in heat transfer was confined to 1.74% for all test fluids in surface tuned minichannel. It was found that the heat transfer in the VUV treated minichannel was superior compared to that in the untreated minichannel at lower Reynolds number ( Re = 294). The results showed that alumina nanofluids performed significantly better than silica nanofluids at a given concentration in both minichannels. The plausible reasons for the enhancement in heat transfer rates in VUV treated minichannels are also discussed.

Chromium can cluster in molten salts

Highly dilute metal ions can aggregate in a high-temperature ionic-liquid medium and form long-lived clusters. The unexpected finding, which is the result of a study that combines experiment and modeling, sheds light on the early stages of corrosion in molten salt reactors (MSRs). MSRs are a next-generation, high-efficiency nuclear power plant technology in which nuclear fuel contained in a high-temperature salt circulates through the reactor in the liquid state. By running roughly 500 °C higher than today’s solid-fuel commercial reactors, MSRs promise to boost thermodynamic efficiency. More than 50 years after researchers began studying MSRs, however, the technology remains under development. One reason is that molten salts can corrode reactor vessels, slowly leaching chromium from alloys that otherwise perform well. To probe the corrosion process at the atomic level, Alexander S. Ivanov of Oak Ridge National Laboratory and coworkers used X-ray scattering and theoretical simulations to study the behavior of

Thermodynamically Induced Transport Anomaly in Dilute Metals ZrTe_{5} and HfTe_{5}.

A 40-year-old puzzle in transition metal pentatellurides ZrTe_{5} and HfTe_{5} is the anomalous peak in the temperature dependence of the longitudinal resistivity, which is accompanied by sign reverses of the Hall and Seebeck coefficients. We give a plausible explanation for these phenomena without assuming any phase transition or strong interaction effect. We show that, due to intrinsic thermodynamics and diluteness of the conducting electrons in these materials, the chemical potential displays a strong dependence on the temperature and magnetic field. With that, we compute resistivity, Hall and Seebeck coefficients in zero field, and magnetoresistivity and Hall resistivity in finite magnetic fields, in all of which we reproduce the main features that are observed in experiments.

Wide Critical Fluctuations of the Field-Induced Phase Transition in Graphite.

In the immediate vicinity of the critical temperature (T_{c}) of a phase transition, there are fluctuations of the order parameter that reside beyond the mean-field approximation. Such critical fluctuations usually occur in a very narrow temperature window in contrast to Gaussian fluctuations. Here, we report on a study of specific heat in graphite subject to a high magnetic field when all carriers are confined in the lowest Landau levels. The observation of a BCS-like specific heat jump in both temperature and field sweeps establishes that the phase transition discovered decades ago in graphite is of the second order. The jump is preceded by a steady field-induced enhancement of the electronic specific heat. A modest (20%) reduction in the amplitude of the magnetic field (from 33 to 27T) leads to a threefold decrease of T_{c} and a drastic widening of the specific heat anomaly, which acquires a tail spreading to two times T_{c}. We argue that the steady departure from the mean-field BCS behavior is the consequence of an exceptionally large Ginzburg number in this dilute metal, which grows steadily as the field lowers. Our fit of the critical fluctuations indicates that they belong to the 3DXY universality class as in the case of the ^{4}He superfluid transition.