Molten NaNO3 Research Articles

Molten salt mediated low-temperature direct roasting of spent lead paste

Traditional pyrometallurgy for recovery of spent lead paste suffered from high energy consumption, massive reducing agent and toxic SOx gas emission. Here, a sustainable molten nitrate salt mediated approach was proposed to realize low-temperature (500 °C) direct roasting of waste lead paste. Efficient desulfurization could not be realized via single direct smelting of the mixture containing spent lead paste, Na2CO3 and NaNO3. The introduction of Na2CO3 desulfurizer could promote the chemical conversion with PbSO4, while the process still required relatively high temperature above 900 °C to realize relatively high desulfurization efficiency. After the introduction of NaNO3 molten salt into spent lead paste-Na2CO3 system, the original solid-solid reaction in spent lead paste-Na2CO3 system was changed to solid-liquid-solid contract, providing more reaction probability between Na2CO3 and PbSO4 phase in spent lead paste. As a result, high-purity lead oxide powders were obtained with 98.7% desulfurization and 99.2% lead recovery ratio. A profit of $378.2 per ton spent lead paste could be achieved from the economically evaluations. The proposed novel pyrometallurgy approach eliminated the emission of harmful SOx from the decomposition of PbSO4 phase and releases of lead containing wastewater, offering a robust lead oxide recovery substitute from secondary lead resources while possessing significant environmental and economic benefits.

Novel value-add recycling route of industry solid waste for acting as supporting skeleton of NaNO3 phase change materials (PCMs)

This study provided a value-added utilization route for industrial solid waste by converting them into porous ceramics to act as supporting skeleton for PCMs. Steel slag (SS), ferronickel-slag (FNS) and Fly ash (FA) was used as main raw material to prepared anorthite-cordierite (AC) porous ceramics. Five groups of formula with different phase content were designed by adjusting the amount of SS and FNS addition. FactSage 8.0 software was applied to calculate the equilibrium phase composition of AC at high temperature, which provided guidance for the actual high temperature synthesis process. The prepared AC porous ceramics were found to have good mechanical strength and high porosity. Good chemical compatibility between AC and NaNO3 was demonstrated and the infiltration ratio was varied from 42% to 45%. In addition to high thermal storage capacity, AC has been found to help reduce the supercooling of NaNO3 and helps to improve the thermal storage performance. After 100 thermal cycles of melting and freezing, NaNO3/AC C-PCMs could maintained high than 97% of latent heat. Thermal transfer properties of AC were significantly enhanced after molten NaNO3 infiltrated. The thermal conductivity of NaNO3/AC40 C-PCMs at 25 °C reached 1.60 W·(m·K)−1, which is more than three times that of pure NaNO3. The good thermal storage performance of NaNO3/AC C-PCMs makes it potential candidate in high-temperature thermal storage fields like industrial waste heat recovery and solar energy storage. In a word, the application potential of metallurgical slag in the field of energy saving was well demonstrated by this study.

Diffusion and release behavior of Ag+ in ion‐exchanged antibacterial glaze

AbstractA potential method for manufacturing antibacterial ceramics can be the incorporation of Ag+ ions into the surface of ceramic glaze via Ag+↔Na+ ion exchange. The ion‐exchange process is usually modulated by the concentration of AgNO3 in the ion‐exchange medium, which, in turn, affects the antibacterial activity. Therefore, the present study investigated the diffusion behavior of Ag+ ions into the glaze at different concentrations (2–10 wt%) of AgNO3 in the ion exchange AgNO3–NaNO3 medium and their release behavior from the ion‐exchanged glaze. The antibacterial activity of the Ag+ ion‐exchanged glaze was also evaluated. As AgNO3 concentration in AgNO3–NaNO3 molten salt increased from 2 to 10 wt%, the diffusion coefficient of Ag+ ions in the molten salt increased from 1.49 × 1021 to 3.84 × 1045 cm2 s−1, and its Nernst distribution coefficient increased from 0.65 to 4.13. This led to the increased incorporation of Ag+ ions in the glaze, which was beneficial for the ion‐exchanged glaze to release Ag+ ions, with the concentration increasing from 0.03 to 0.10 μg mL−1 cm−2 in 24 h, and maintain leaching of the Ag+ ions for a long time to exert long‐term antibacterial activity.

Probing the Local Structure of Na in NaNO3-Promoted, MgO-Based CO2 Sorbents via X-ray Absorption Spectroscopy.

This work provides insight into the local structure of Na in MgO-based CO2 sorbents that are promoted with NaNO3. To this end, we use X-ray absorption spectroscopy (XAS) at the Na K-edge to interrogate the local structure of Na during the CO2 capture (MgO + CO2 ↔ MgCO3). The analysis of Na K-edge XAS data shows that the local environment of Na is altered upon MgO carbonation when compared to that of NaNO3 in the as-prepared sorbent. We attribute the changes observed in the carbonated sorbent to an alteration in the local structure of Na at the NaNO3/MgCO3 interfaces and/or in the vicinity of [Mg2+···CO32-] ionic pairs that are trapped in the cooled NaNO3 melt. The changes observed are reversible, i.e., the local environment of NaNO3 was restored after a regeneration treatment to decompose MgCO3 to MgO. The ex situ Na K-edge XAS experiments were complemented by ex situ magic-angle spinning 23Na nuclear magnetic resonance (MAS 23Na NMR), Mg K-edge XAS and X-ray powder diffraction (XRD). These additional experiments support our interpretation of the Na K-edge XAS data. Furthermore, we develop in situ Na (and Mg) K-edge XAS experiments during the carbonation of the sorbent (NaNO3 is molten under the conditions of the in situ experiments). These in situ Na K-edge XANES spectra of molten NaNO3 open new opportunities to investigate the atomic scale structure of CO2 sorbents modified with Na-based molten salts by using XAS.

Effects of alkali-metal nitrate salts on hydrotalcite-based sorbents for enhanced cyclic CO2 capture at high temperatures

CO2 capture using solid-based adsorbents at high temperatures has been in the spotlight as a CO2 capture and storage (CCS) technology for solving global warming and climate change problems. Hydrotalcite is an anionic clay that is widely used as a CO2 sorbent at temperatures of 200–400 °C. In various methods to improve the relatively low CO2 uptake of hydrotalcite, the hydrotalcites with a high Mg/Al molar ratio achieved significantly increased CO2 sorption uptake. This was because the preparation method allowed incorporation of NaNO3 in the hydrotalcite structure; the maximum CO2 sorption uptake was measured as 28.4 wt% when the Mg/Al molar ratio was 30. The different degrees of NaNO3 melting, depending on the sorption temperature, led to different CO2 sorption kinetics and uptakes at 250, 275, and 300 °C. Over the repeated sorption-desorption cycles, the CO2 cyclic capacity continuously decreased under sorption at 250 and 275 °C, whereas it increased at 300 °C, regardless of the Mg/Al molar ratio. The partial melting of NaNO3 at 250 and 275 °C, below its melting temperature, provided insufficient rearrangement of molten NaNO3. This further caused sintering of the MgO structure, which also increased its crystallite size. Conversely, the accelerated rearrangement of molten NaNO3 at 300 °C, near its melting temperature, and the low CO2 uptake at the initial step inhibited sintering. Different changes in the strength of CO2 sorption on the hydrotalcite-based sorbents also appeared as the cycle number increased.

Novel low-cost steel slag porous ceramic-based composite phase change material: An innovative strategy for comprehensive utilization of steel slag resources

This work creatively proposes a novel and low-cost steel slag porous ceramic (SSPC)-based NaNO3 salt composite phase change material (PCM) using industrial solid waste steel slag as the main raw material. In this study, the foaming-gel casting process prepares SSPC with high porosity (77–83%) and mechanical strength (0.36–1.13 MPa), which shows good adsorption of NaNO3 salts. The spontaneous infiltration method prepares and characterizes the NaNO3/SSPC composite PCM by performance properties. The results show that the NaNO3 salt is uniformly adsorbed in the pores of SSPC with good chemical compatibility, and the maximum filling rate reaches 86.26%. The porous media can effectively prevent the leakage of molten NaNO3 salt. The prepared composite PCMs have lower melting and freezing temperatures, lower subcooling by 5.47 °C, and higher thermal conductivity by 121.6% compared to pure NaNO3 salt. The latent heat retention of the composite after 50 thermal cycles is more than 96%, with good thermal reliability. Finally, a prospective process of using steel slag to prepare composite PCMs for collecting and storing waste heat from the steel industry is proposed. Reusing steel slag and storing waste heat from the steel industry are realized, both beneficial for sustainable development.

Preparation and characterization of NaNO3 shape-stabilized phase change materials (SS-PCMs) based on anorthite ceramic and cordierite ceramic for solar energy storage

In the current study, molten NaNO3 shape-stabilized phase change materials (SS-PCMs) based on anorthite ceramic and cordierite ceramic were prepared by cold-press sintering method. Chemical compatibility and wettability were considered simultaneously to determine whether the ceramics were qualified as supporting skeleton and the enhancement of the thermal properties of NaNO3 by the ceramics was also investigated. It was found that both anorthite ceramic and cordierite ceramic have good chemical compatibility with NaNO3 and no chemical reaction occurred between them. Physical compatibility was evaluated by measuring the contact angle of molten NaNO3 on a ceramic substrate. Cordierite ceramic exhibited better wettability than anorthite ceramic, although both of the contact angles decreased gradually with increasing temperature. The supercooling of the prepared anorthite ceramic-based SS-PCMs with 45 wt% NaNO3 (45ASS-PCMs) was only 0.7 °C, which was less than 2.5 °C for pure NaNO3 and 2.0 °C for cordierite ceramic-based SS-PCMs with 45 wt% NaNO3 (45CSS-PCMs). The phase transition enthalpy loss of 45ASS-PCMs after 100 thermal cycles was less than 2%, while 45CSS-PCMs reached more than 5%. Anorthite ceramic showed better capabilities than cordierite ceramic in terms of thermal reliability and stability, while cordierite ceramic was better than anorthite ceramic in enhancing thermal conductivity. The evaluation method proposed in this study provided favorable guidance for the matching of PCMs and ceramic supporting skeleton.

Palygorskite Supporting Homogeneously Dispersed Ag Nanoparticles: Molten Salt Method and Enhanced Antibacterial Performance

AbstractSupported silver nanoparticles (Ag NPs) have been used extensively as antibacterial agents in biomedicine, biotechnology, and environmental remediation. However, a facile and scalable method for preparing Ag NPs dispersed homogeneously on supports remains a challenge. In this study, a novel molten salt method was developed successfully to synthesize the supported, homogeneously dispersed Ag NPs on palygorskite. Abundant pores and ample surface hydroxyl groups of palygorskite served as anchoring sites, preventing the rapid growth, aggregation, and sintering of Ag NPs. Typically, palygorskite was mixed with AgNO3 (as a precursor) and NaNO3 (as a dispersant), and then the mixture was heated slowly. During the heating process, the AgNO3 decomposed gradually into Ag NPs and the molten NaNO3 with a high concentration of ions dispersed the newly formed Ag NPs. The Ag NPs were dispersed homogeneously on the palygorskite and had very small particle sizes (~5.8 nm) even for a significant loading amount (~9 wt.%). As antibacterial agents, the Ag/palygorskite nanocomposites showed enhanced antibacterial activity, compared with those synthesized without the introduction of molten NaNO3. In addition, the key effect of the surface hydroxyl groups of palygorskite on the characteristics of the loaded Ag and the corresponding antibacterial activity were also elucidated. As such, the present work provided a novel and facile strategy for the synthesis, without a chemical reductant or surfactant, of supported, highly dispersed Ag NPs on clay minerals and this could have potential in the scalable production and practical application of Ag-based antibacterial materials.

Uncovering the CO2 Capture Mechanism of NaNO3-Promoted MgO by 18O Isotope Labeling.

MgO-based CO2 sorbents promoted with molten alkali metal nitrates (e.g., NaNO3) have emerged as promising materials for CO2 capture and storage technologies due to their low cost and high theoretical CO2 uptake capacities. Yet, the mechanism by which molten alkali metal nitrates promote the carbonation of MgO (CO2 capture reaction) remains debated and poorly understood. Here, we utilize 18O isotope labeling experiments to provide new insights into the carbonation mechanism of NaNO3-promoted MgO sorbents, a system in which the promoter is molten under operation conditions and hence inherently challenging to characterize. To conduct the 18O isotope labeling experiments, we report a facile and large-scale synthesis procedure to obtain labeled MgO with a high 18O isotope content. We use Raman spectroscopy and in situ thermogravimetric analysis in combination with mass spectrometry to track the 18O label in the solid (MgCO3), molten (NaNO3), and gas (CO2) phases during the CO2 capture (carbonation) and regeneration (decarbonation) reactions. We discovered a rapid oxygen exchange between CO2 and MgO through the reversible formation of surface carbonates, independent of the presence of the promoter NaNO3. On the other hand, no oxygen exchange was observed between NaNO3 and CO2 or NaNO3 and MgO. Combining the results of the 18O labeling experiments, with insights gained from atomistic calculations, we propose a carbonation mechanism that, in the first stage, proceeds through a fast, surface-limited carbonation of MgO. These surface carbonates are subsequently dissolved as [Mg2+···CO3 2-] ionic pairs in the molten NaNO3 promoter. Upon reaching the solubility limit, MgCO3 crystallizes at the MgO/NaNO3 interface.

Numerical simulation of natural convection and heat transfer in a molten pool with embedded cooling tubes

This study described the natural circulation and heat transfer of a molten pool in a specifically designed core catcher conceived for a pressurized water reactor. In addition to external cooling, the core catcher features internal cooling tubes embedded in the molten pool. To investigate the coolability in such a configuration, first, a full-scale core catcher simulation is conducted to give a preliminary study under a real SA situation. Results illustrated that cooling efficiency can be remarkably enhanced due to the inner tubes. Then a test facility of the 2D slice with the geometrical scaled factor of 1:4 has been developed, and molten salt (NaNO3–KNO3) experiments will be implemented in the near future. This study also performed a pre-test simulation using molten NaNO3–KNO3 as a stimulant to study the heat transfer and flow characteristics of the salt pool. The melt convection in the test section was represented by a two-dimensional mesh with a WMLES turbulence model using the FLUENT code. The simulation captured the heat transfer enhancement by the cooling tubes as expected, and the results would help decide the proper test matrix and improvement of instrumentation required to obtain the necessary data for code validation.

Polymorphism and sodium-ion conductivity of NaTa2PO8 synthesized via the Li+/Na+ ion-exchange reaction of LiTa2PO8

Ion exchange reaction is a promising method to explore metastable compounds that could not be synthesized by conventional high-temperature solid-phase reactions. Herein, a new sodium tantalum phosphate, NaTa2PO8 was synthesized via the Li+/Na+ ion-exchange reaction of the parent compound, LiTa2PO8 in molten NaNO3 medium. NaTa2PO8 underwent an irreversible phase transition from the low- (LT-NaTa2PO8) to the high-temperature polymorph (HT-NaTa2PO8) at approximately 1000 °C. The crystal structures were solved using an ab initio structural determination method based on synchrotron X-ray powder diffraction data. The LT-NaTa2PO8 presented an orthorhombic structure, closely related to that of the parent LiTa2PO8 structure. In contrast, the HT-NaTa2PO8 was found to adopt a monoclinic structure, belonging to a family of monophosphate tungsten bronzes with pentagonal tunnels. The ionic conductivities of LT-NaTa2PO8 (σ = 5 × 10−5 S/cm at 309 °C) and HT-NaTa2PO8 (σ = 2 × 10−7 S/cm at 300 °C) exhibited Arrhenius behavior with activation energies of 0.49 and 0.79 eV, respectively. Bond valence energy landscape (BVEL) calculations indicated that a three-dimensional (3D) conduction pathway is formed in LT-NaTa2PO8 structure, while the conduction pathway in HT-NaTa2PO8 shows a two-dimensional (2D) character.

Aluminum doping of mesoporous silica as a promising strategy for increasing the energy storage of shape stabilized phase change materials containing molten NaNO3: KNO3 eutectic mixture

Efficient thermal energy storage at high temperature is necessary for both industrial waste heat utilization and continuous solar power generation. Shape-stabilized phase change materials containing mesoporous aluminosilicates and eutectic NaNO3: KNO3 (1:1 mol) molten salt mixture were obtained at 90% wt. salt. The influence of aluminum doping was studied for the first time. All samples show thermal stability up to 550 °C and two distinct phase transitions corresponding to the melting/freezing of nanoconfined and interparticle salt phases. The radius and spherical shape of the nanoconfined phase were determined from the melting and freezing point depressions with respect to bulk. The enthalpy decrease was quantified in terms of surface tension and the contributions of a non-melting fraction of surface adsorbed ions. SBA-15 type aluminosilicates matrices yield composites with high latent heat storage of 76–77 Jg−1, of which 8 Jg−1 for the nanoconfined phase and good thermal reliability. Aluminum doping is a simple and promising strategy for obtaining high temperature, efficient thermal energy storage materials due to a lack of non-melting salt fraction. The resulting shape-stabilized PCMs have a higher operating temperature range and latent heat storage, offering a 36% increase in total heat capacity over the pristine salt.

The corrosion behavior of 304 stainless steel in NaNO3-NaCl-NaF molten salt and vapor.

Corrosion behavior of 304 stainless steel in molten NaNO3–NaCl–NaF salt and NaNO3–NaCl–NaF vapor has been studied at 450 °C. The results showed that the samples suffered weight loss, and surface oxides, i.e. Fe2O3 and FeCr2O4 characterized by XRD, were formed after corrosion. The surface oxide layer was about 1.1 μm in thickness after corrosion in molten NaNO3–NaCl–NaF salt, which was relatively homogeneous and dense. Whereas, the distribution of surface oxides was not even, and a shedding phenomenon was observed after corrosion molten NaNO3–NaCl–NaF vapor. This is mainly attributed to the existence of NO2 and NO in the molten NaNO3–NaCl–NaF vapor determined by thermogravimetric infrared spectroscopy, which affected the adherence between oxides and the matrix. Additionally, the corrosion rate of 304 stainless steel in molten NaNO3–NaCl–NaF salt is almost close to that in solar salt, which demonstrates that the synergy influence of Cl− and F− on the rate of 304 stainless steel is not significant. This work not only enriches the database of molten salt corrosion, but provides references for the selection of alloy and molten salt in the CSP.

Unravelling the Mechanism of Intermediate-Temperature CO2 Interaction with Molten-NaNO3 -Salt-Promoted MgO.

The optimization of MgO-based adsorbents as advanced CO2 -capture materials is predominantly focused on their molten-salt modification, for which theoretical and experimental contributions provide great insights for their high CO2 -capture performance. The underlying mechanism of the promotion effect of the molten salt on CO2 capture, however, is a topic of controversy. Herein, advanced experimental characterization techniques, including in situ environmental transmission electron microscopy (eTEM) and CO2 chemisorption by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), transient 18 O-isotopic exchange, and density functional theory (DFT), are employed to elucidate the mechanism of the CO2 interaction with molten-salt-modified MgO in the 250-400°C range. Herein, eTEM studies using low (2-3 mbar) and high (700 mbar) CO2 pressures illustrate the dynamic evolution of the molten NaNO3 salt promoted and unpromoted MgO carbonation with high magnification (<50nm). The formation of 18 O-NaNO3 (use of 18 O2 ) and C16 O18 O following CO2 interaction, verifies the proposed reaction path: conversion of NO3 - (NO3 - → NO2 + + O2- ), adsorption of NO2 + on MgO with significant weakening of CO2 adsorption strength, and formation of [Mg2+ … O2- ] ion pairs preventing the development of an impermeable MgCO3 shell, which largely increases the rate of bulk MgO carbonation.

Understanding relationship of sepiolite structure tailoring and the catalytic behaviors in glycerol steam reforming over Co/sepiolite derived Co-phyllosilicate catalyst

Bio-glycerol Steam reforming over green and economical Co/sepiolite (SEP) catalysts was a promising strategy to hydrogen production. The activation pretreatment of SEP played a vital role for boosting catalytic behavior of Co/SEP. This work originally explored a full activation of SEP by molten NaOH for tailoring the physicochemical properties of Co-based catalysts prepared by urea precipitation method. Differing from the acid pickling/calcination and molten NaNO3 activation, the molten NaOH treatment enhanced surface area of SEP by desilicication/dealumination effect and further improved the exposure of framework Si and its surface ‘reactivity’. According to the characterization results of N2 adsorption-desorption, XRD, TEM, H2-TPR, CO/CO2-TPD and XPS, it was found that the feathered Co-phyllosilicate formed on Co/SEP-NaOH catalyst, which enhanced the metal-support interaction, surface area and basic/metallic sites. In contrast, the molten NaNO3 treatment facilitated the transformation of SEP into loughlinite and it was adverse to metal dispersion. Therefore, Co/SEP-NaOH catalyst possessed the highest conversion (92%) and H2 yield (68%) during the activity test at 600 °C and the superior resistance to amorphous coke. Additionally, DFT analysis was introduced to simulate the process of glycerol adsorption and decomposition and demonstrated the Co–CoO interface as the primary reaction sites for the catalytic process.

A Comparative Study of High-Temperature Latent Heat Storage Systems

High-temperature latent heat storage (LHS) systems using a high-temperature phase change medium (PCM) could be a potential solution for providing dispatchable energy from concentrated solar power (CSP) systems and for storing surplus energy from photovoltaic and wind power. In addition, ultra-high-temperature (&gt;900 °C) latent heat storage (LHS) can provide significant energy storage density and can convert thermal energy to both heat and electric power efficiently. In this context, a 2D heat transfer analysis is performed to capture the thermo-fluidic behavior during melting and solidification of ultra-high-temperature silicon in rectangular domains for different aspect ratios (AR) and heat flux. Fixed domain effective heat capacity formulation has been deployed to numerically model the phase change process using the finite element method (FEM)-based COMSOL Multiphysics. The influence of orientation of geometry and heat flux magnitude on charging and discharge performance has been evaluated. The charging efficiency of the silicon domain is found to decrease with the increase in heat flux. The charging performance of the silicon domain is compared with high-temperature LHS domain containing state of the art salt-based PCM (NaNO3) for aspect ratio (AR) = 1. The charging rate of the NaNO3 domain is observed to be significantly higher compared to the silicon domain of AR = 1, despite having lower thermal diffusivity. However, energy storage density (J/kg) and energy storage rate (J/kgs) for the silicon domain are 1.83 and 2 times more than they are for the NaNO3 domain, respectively, after 3.5 h. An unconventional counterclockwise circular flow is observed in molten silicon, whereas a clockwise circular flow is observed in molten NaNO3 during charging. The present study establishes silicon as a potential PCM for designing an ultra-high-temperature LHS system.

Improved thermal conductivity of form-stable NaNO3: Using the skeleton of porous ceramic modified by SiC

Corrosion and low thermal conductivity are considered as two great challenges for the application of salts-based phase change materials (PCMs). To address these problems, a novel skeleton, namely SiC modified diatomite-based porous ceramic, was prepared to develop form-stable NaNO3 salt. The results showed that a good wettability and chemical compatibility existed between SiC and molten NaNO3. Thermal conductivity of composite PCMs was found to be nearly linearly related with the concentration of SiC. 20% SiC added into the skeleton helped to enhance thermal conductivity of composites by 50%, benefited by the formation of a high thermally conductive heat transfer path. A smaller particle size of SiC contributed to a higher thermal conductivity of composites by increasing the heat transfer area between PCMs and skeleton. Form-stable NaNO3 (56.6%) that had a skeleton modified by 10% SiC (only 4.3% in composites) with particle size of 50 nm possessed a thermal conductivity of 2.06 W/(m·K) at 25 °C, which was 265% higher than that of pure NaNO3. Such composites also performed quite a good stability during the 500 thermal cycles, in terms of chemical compatibility, thermal conductivity, latent heat, phase transition temperature, and mechanical strength. Therefore, the novel composite PCMs exhibited a great application prospect in thermal energy storage.

Electroless Ni–P coatings on low-Cr steels: A cost-efficient solution for solar thermal applications

The corrosion behavior of an electroless Ni–P coating on low-Cr X20CrMoV12-1 steel as a cost-efficient substrate-coating combination is investigated in molten NaNO 3 –KNO 3 nitrates at 600 °C. Results indicated that the as-deposited Ni–P coating was transformed to a thermally treated diffusion coating upon exposure to the molten salt without additional heat treatment prior to the exposure. Detailed evolution of the Ni–P coating and the oxidation behavior during the 1000-h immersion test is discussed. Results showed competitive corrosion resistance of the coating system compared to that of the sophisticated Ni alloy 230, with the advantage of an inherent barrier against Cr dissolution form the substrate. The significant corrosion resistance of the electroless plated Ni–P coating is attributed in part to the protective Ni--rich oxide scale and in other part to the in-situ formed Ni 3 P barrier at the oxide-substrate interphase boundary. - Electroless Ni–P coating was developed on a low-cost X20CrMoV12-1 substrate - Interdiffusion occurred during the immersion test at 600 °C - The as-coated substrate required no additional heat treatment prior to the molten salt exposure - An outer Ni–Cr rich oxide scale and an inner Ni 3 P layer formed during the immersion test - The Ni–Cr scale and Ni 3 P layer protected the substrate against molten salt corrosion and Cr-dissolution

Influence of partial components removal on pyrolysis behavior of lignocellulosic biowaste in molten salts

Using molten NaNO3–KNO3–NaNO2 for biowaste pyrolysis provides a promising way to synergize the utilization of biowaste and fluctuating solar energy. However, the diversity of lignocellulosic biowaste and violent decomposition complicated the interactions between natural constituents. In this study, the pyrolysis behavior of woody and agricultural herbaceous lignocellulosic biowaste in molten salts was comprehensively investigated at 300 °C. Through the selective removal of partial hemicellulose or lignin, the specific role of the original structure on the products formation characteristics was further estimated. The results showed that more volatiles were released from the hemicellulose-enriched agricultural herbaceous biowaste than cellulose-enriched woody biowaste. The yields of water and organic liquids from hemicellulose or lignin removal were higher than that of raw biowaste. Specifically, hemicellulose dominated the generation of nitrogenous substances in the liquid products. As for the gas product, its yield from the hemicellulose removal sample was higher than raw biowaste but it decreased after removing lignin. Lignin was the primary contributor to the combustible CO, H2, and CH4, while the production of CO2 was more affected by hemicellulose. The lignin would compete with hemicellulose and be superior to the latter in the reaction with molten salt.

Highly conductive titania supported iridium oxide nanoparticles with low overall iridium density as OER catalyst for large-scale PEM electrolysis

To enable future large-scale generation of hydrogen via proton exchange membrane (PEM) electrolysis, utilization of scarce iridium-based catalysts required for the oxygen evolution reaction (OER) has to be significantly lowered. To address this question, the facile synthesis of a highly active TiO2 supported iridium oxide based OER catalyst with reduced noble metal content and an Ir-density of the catalyst powder as low as 0.05–0.08 gIr cm-3 is described in this work. A high surface area corrosion-resistant titania catalyst support homogeneously coated with a 1-2 nm thin layer of amorphous IrOOHx is oxidized in molten NaNO3 between 350-375°C. This procedure allows for a controllable phase transformation and crystallization to form a layer of interconnected IrO2 nanoparticles of ≈2 nm on the surface of the TiO2 support. The increase in crystallinity is thereby accompanied by a significant increase in conductivity of up to 11 S cm-1 for a 30 wt% Ir loaded catalyst. Oxidized samples further display a significantly increased stability with less detectable Ir dissolution under OER conditions. With a mass-based activity of 59 A g-1 at an overpotential of 300 mV, the electrocatalytic activity is maintained at the level of the highly active amorphous IrOOHx phase used as precursor and outperforms it at higher current densities through the increased conductivity. MEA measurements with catalyst loadings of 0.2-0.3 mg cm-2 further confirm the high catalytic activity and initial stability at industrially relevant current densities. The introduced synthesis approach therefore shows a path for the fabrication of novel highly active and atom-efficient oxide supported catalysts with complex nanostructures and thin homogenous nanoparticle coatings that allows a future large-scale application of PEM electrolysis technology without restrictions by the natural abundance of iridium.