Neighbor Sites Research Articles

Polyethylene hydrogenolysis by dilute RuPt alloy to achieve H2-pressure-independent low methane selectivity

Chemical recycling of plastic waste could reduce its environmental impact and create a more sustainable society. Hydrogenolysis is a viable method for polyolefin valorization but typically requires high hydrogen pressures to minimize methane production. Here, we circumvent this stringent requirement using dilute RuPt alloy to suppress the undesired terminal C–C scission under hydrogen-lean conditions. Spectroscopic studies reveal that PE adsorption takes place on both Ru and Pt sites, yet the C–C bond cleavage proceeds faster on Ru site, which helps avoid successive terminal scission of the in situ-generated reactive intermediates due to the lack of a neighboring Ru site. Different from previous research, this method of suppressing methane generation is independent of H2 pressure, and PE can be converted to fuels and waxes/lubricant base oils with only <3.2% methane even under ambient H2 pressure. This advantage would allow the integration of distributed, low-pressure hydrogen sources into the upstream of PE hydrogenolysis and provide a feasible solution to decentralized plastic upcycling.

Analysis of scale-dependent spatial correlations of actual evapotranspiration measured by lysimeters

Accurate determination of actual evapotranspiration (ETa) is important in various research fields like hydrology, meteorology, ecology and agriculture. In situ ETa can be determined using weighing lysimeters and eddy covariance. However, despite being regarded as the most precise in situ method for measuring ETa, the information content of lysimeter measurements remains poorly understood. Here we examined the spatial correlations between ETa measured at different locations by lysimeter (ET-LYS) and at different locations by eddy covariance (ET-EC). This was done for the period 2015 - 2020 and the analysis was made for different spatial (range: 0 to 500 km) and temporal scales (range: 1 day to 1 year) using 23 lysimeters and 4 eddy covariance towers. We found that: (a) Same lysimeters at the plot scale show very high correlations of ET-LYS; (b) The Pearson correlation of daily standardized anomalies of ET-LYS between sites exhibit moderate to high correlations and were similar to that of ET-EC, indicating that lysimeter is generally as representative as EC regarding ETa, and can provide certain information at the landscape and larger regional scale. During winter, the spatial correlations for ET-LYS were smaller; (c) Wavelet analysis indicated that temporal correlations in ETa were strongest for distances in time around 12 months (yearly cycle) and less than three months. Spatial correlations were smaller under drought conditions (in the year 2018). Furthermore, combination of multiple ET-LYS from different sites improved the predictability of ET-LYS for another site, suggesting that ET-LYS can be predicted well using ET-LYS from different neighboring sites. Overall, lysimeter measurements can provide information at much larger scales compared to their small measurement area.

Insight into heterovalent metal modification for lanthanum carbonate to enhance phosphate removal at trace levels

Reducing phosphate concentrations from low levels to ultra-low levels (e.g., below 0.01 mg P/L) is crucial for preventing and treating eutrophication. Adsorption is promising but still challenged by the limited adsorption capacity at low phosphate concentrations, which leads to high costs. Herein, we propose a heterovalent metal modification strategy using Fe(II) to improve the adsorption capacity of lanthanum (La) carbonate for low-level phosphate removal. A La:Fe(II) molar ratio of 7:1 enabled the partial substitution of Fe(II) for La, resulting in a La/Fe carbonate with a high adsorption capacity. La/Fe carbonate exhibited fast adsorption kinetics, excellent applicability in a pH range of 5–7, and good reusability at low phosphate concentrations. Its adsorption capacity at low phosphate levels surpassed previously reported adsorbents. La/Fe carbonate demonstrated high resistance to complex water matrices and cost-effectiveness, achieving an effluent concentration below 0.01 mg P/L in real wastewater treatment. Mechanism analysis revealed that Fe(II) substitution led to super-saturated coordination and Fe(II) → Fe(III) conversion for charge compensation. The self-conversion of Fe(II) → Fe(III) donated electrons to neighboring La active sites, activating these active centers, which caused a positive shift in the d-band center of La active sites and enhanced interfacial electron transport between La/Fe carbonate and phosphate. This work offers an efficient, easy-to-operate, and low-cost approach to achieve ultra-low phosphate concentrations through adsorption, and fills the research gap on the mechanism of heterovalent metal modulation to enhance the phosphate adsorption capacity.

Electronic and optical properties of Cr-Mn co-doped in monolayer MoS2: A first-principles study

The effects of Cr-Mn co-doping of neighboring and spacer sites on the electronic and optical properties of monolayer molybdenum disulfide (ML-MoS2) are investigated using a first-principles plane-wave pseudopotential method based on density-functional theory (DFT). The results show that the band structure (BS) and the bandgap of pristine ML-MoS2 are in good agreement with the available experimental and theoretical data. Electronic analysis implies that the bandgap of Cr-Mn co-doped ML-MoS2 is smaller than that of the pristine ML-MoS2 and the bandgap of Cr-Mn co-doped ML-MoS2 at spacer sites is the smallest. Moreover, the ML-MoS2 changes from a direct bandgap to an indirect bandgap semiconductor, which facilitates electron-hole pair transfer. In addition, pristine ML-MoS₂ has no magnetism, while Cr-Mn co-doped ML-MoS2 at neighboring and spacer sites present ferromagnetism. Studies of optical properties have shown that doped ML-MoS2 systems, especially Cr-Mn co-doped at spacer sites, exhibit higher sensitivity to visible and ultraviolet (UV) light along the x-axis as well as to UV light along the z-axis. This suggests the possibility of applications in photodetectors, solar cells, and photocatalysis. It is noteworthy that Cr-Mn co-doping at the spacer sites significantly improves the photovoltaic performance and light utilization efficiency of ML-MoS2 by increasing the dielectric tensor, absorption coefficient, and photoconductivity while decreasing the extinction coefficient compared with pristine ML-MoS2.

Fluoride Ion Storage and Conduction Mechanism in Fluoride Ion Battery Positive Electrode, Ruddlesden-Popper-Type Layered Perovskite La1.2Sr1.8Mn2O7 Crystal.

Structural characteristics on fluoride ion storage and conduction mechanism in La1.2Sr1.8Mn2O7, and its fluoridated materials, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, for an all-solid-state fluoride ion battery positive electrode with a high volumetric capacity surpassing those of lithium-ion ones have been revealed using the Rietveld method and maximum entropy method. In La1.2Sr1.8Mn2O7, once the F- ions are taken into the NaCl slabs in its crystal through the charging process, it forms two stable fluoride compounds, La1.2Sr1.8Mn2O7F and La1.2Sr1.8Mn2O7F2, with the help of the Mn oxidation reaction. In these oxyfluorides, thermal vibrations of the F- ions inserted are much larger, especially in the a-b plane, than along the c axis. When surplus energy, such as an electric field for charging, is applied to these crystals at near room temperature or higher, the anions immediately begin to jump to their neighboring lattice sites, resulting in sufficiently rapid and large ionic conduction. The MEM analyses and density functional theory (DFT) calculations have revealed that the F- ions enable to easily travel along the ⟨110⟩ directions in the NaCl slabs of these crystals. These structural features thus make La1.2Sr1.8Mn2O7 and its fluorides possess both of two features incompatible with each other, ion storage and conduction, indispensable for rechargeable batteries.

An ab-initio investigation of Sc and Y doped chalcopyrite MgGeN[formula omitted]

The doping of Scandium and Yttrium within chalcopyrite MgGeN2 were computationally investigated using density function theory (DFT) calculations. By calculating the formation energy, it was shown that independent single Sc and Y dopants energetically favor the occupation of the Mg site, inducing a shallow level within the conduction band. However, in the presence of a substitutional defect, the second dopant will occupy the neighboring Ge site. There is strong attractive interaction between two dopants, so that they are easily combined into a composite defect. In this case a shallow defect level appears above the valence band edge. Similar behavior is observed for the composite defects containing one dopant and an intrinsic cation vacancy, while those with one dopant and a nitrogen vacancy induce a deep defect level and greatly reduce the band gap. The investigation deepens the knowledge of Sc and Y doped II-IV-V2 compounds and may hence lead to more implementations.

Chemistry of Formate and Water Ligands on Metal Oxide Cluster Nodes of Metal-Organic Framework hcp Hf-UiO-66: Keys to Understanding Reactivity of Paired μ2-OH and Defect Sites.

Many metal-organic frameworks (MOFs) incorporate nodes that are metal oxide clusters, and ligands that have been observed on these nodes include formates, acetates, water, hydroxyl groups, and others, all of which are potentially important in affecting reactivities for applications in separations, catalysis, and sensing. Formate is a common node ligand, arising from formic acid used as a modulator and from N,N-dimethylformamide used as a solvent in MOF syntheses. Yet only little work has been reported characterizing the reactivities of node formate ligands. Infrared spectra reported here show that formate bonds to two types of sites on the paired Hf6O8 nodes of hcp UiO-66, namely, defect and μ2-OH sites. Quantifying the number of formate ligands by 1H NMR spectroscopy of digested samples showed an almost equal number of formate ligands on the two sites, indicating the likelihood that they neighbor each other. These formate ligands interact with water molecules, reversibly switching their bonding from bidentate to monodentate. The formates on μ2-OH sites of hcp Hf-UiO-66 interact much more strongly with water than those on defect sites of the same node, and both interact more strongly than isolated defect sites of Hf-UiO-66. Correspondingly, the catalytic activities of hcp UiO-66 determined as turnover frequencies on each site are approximately twofold higher than those on UiO-66, bolstering the inference that methanol dehydration is catalyzed by a node defect site and a neighboring node μ2-OH site. The results show how MOFs, with their well-defined node structures, provide unprecedented opportunities to understand details of reactivities and catalysis on metal oxide clusters, in contrast to bulk metal oxide surfaces.

Construction of Fe/Co-N4 Single-Atom Sites for the Oxygen Reduction Reaction in Zinc-Air Batteries.

Insight into the modulation effect of oxygen reduction reaction (ORR) active centers is of profound significance but remains a great challenge. Here, we designed Co, Fe dual-metal single-atom sites (CoFe-DSAs/NC) uniformly anchored on nitrogen-doped multiwalled carbon nanotubes for boosting ORR performance through regulating the 4d electronic orbitals of the Co-N4 active site. Mechanism studies revealed that for the first time the neighboring Fe-N4 atomic sites were able to regulate the d-band center of Co-N4 single-atom active centers while maintaining the balance of adsorption-desorption affinity for O2 and oxygen-containing species on Co-N4, thereby resulting in a superior ORR performance with a positive half-wave potential (0.90 V vs RHE). The assembled zinc-air battery based on CoFe-DSAs/NC exhibited an increased open-circuit voltage (1.48 V) and an elevated specific capacity (782.33 mAh·g-1). The work provides a new clue for reasonably designing high-performance ORR catalysts through adjusting the d-band center of active sites.

A new hybrid deep neural network for multiple sites PM2.5 forecasting

Many studies have confirmed that fine particulate matter (PM2.5) poses significant hazards to both human health and the ecological environment. Predicting future trends in PM2.5 concentrations is crucial for preventing air pollution hazards to human health. However, current machine learning-based forecasting models often focus on specific regions or sites, resulting in poor spatial generalization performance. To address this issue, this study utilizes ERA5 meteorological reanalysis data, MERRA2 assimilated aerosol optical depth (AOD) data, and ground pollutant monitoring site data to construct a three-dimensional dataset. A novel hybrid deep neural network model (D_GAT) is proposed to simultaneously forecast the future 72h PM2.5 concentration trends for all sites in China. The D_GAT model combines the advantages of a graph attention network and a long short-term memory neural network, which can effectively aggregate spatial information between sites and simulate the spatial transport process and time series change characteristics of pollutant particles. Moreover, the proposed calculation method for attention scores quantified based on the actual pollutant propagation characteristics, combined with the upper atmosphere pollution transport process represented by AOD, can better express the pollution contributions of different neighboring sites to the predicted central site. Experimental results show that, compared to four other baseline models, the novel model achieves an average R2 of 0.732 for all sites in 72-h prediction, which is the highest among the five models, and the prediction accuracy of 72h is also in the forefront compared with the current similar research. The RMSE and MAE are 14.63 μg/m3 and 9.49 μg/m3, respectively, which are 2–4 μg/m3 lower than the other four baseline models, indicating that it has higher reliability and can achieve the goal of timely prediction and early warning. Overall, the new model is an effective tool for multiple sites generalization forecasting.

Phosphor-doping modulates the d-band center of Fe atoms in Fe-N4 catalytic sites to boost the activity of oxygen reduction

Regulating the electronic structure by phosphor-doping is a preferred strategy to boost the performance of carbon-based catalysts for oxygen reduction reaction (ORR). Here, a porous Fe, P, N-codoped carbon catalyst (PCF-FeTz-900) is designed by a phytic acid-assisted thermal etching strategy, in which P atoms are first doped into the carbon matrix to form a stable PC bond, and then FeN4 sites are produced from Fe-2,4,6-Tris(2-pyridyl)-s-triazine complex (Fe-TPTz). Theoretical calculations suggest that the electrons are transferred from the doped P atom to the neighboring FeN4 sites, which facilitates the ORR at the Fe sites by reducing the energy barrier and the adsorption energy of intermediates. Additionally, the P-doped FeN4 (FeN4P) structure manifests a lower free energy difference than that of FeN4 and the d-band center of Fe is also lowered, which further ensures its higher ORR catalytic ability. As a result, the PCF-FeTz-900 catalyst exhibits superior ORR activity and stability in alkaline electrolyte, and the assembled primary zinc-air battery shows greater performances compared to the commercial Pt/C catalyst. This work can provide an effective pathway for modulating the performance of doped-carbon materials in energy conversion devices.

Unraveling the Origin of the Repulsive Interaction between Hydrogen Adsorbates on Platinum Single-Crystal Electrodes.

Hydrogen adsorption on platinum (Pt) single-crystal electrodes has been studied intensively in both experiments and computations. Yet, the precise origin and nature of the repulsive interactions observed between hydrogen adsorbates (Hads) have remained elusive. Here, we use first-principles density functional theory calculations to investigate in detail the interactions between Hads on Pt(111), Pt(100), and Pt(110) surfaces. The repulsive interaction between Hads on Pt(111) is deconvoluted into three different physical contributions, namely, (i) electrostatic interactions, (ii) surface distortion effect, and (iii) surface coordination effect. The long-range electrostatic interaction, which is generally considered the most important source of repulsive interactions in surface adsorption, was found to contribute less than 30% of the overall repulsive interaction. The remaining >70% arises from the other two contributions, underscoring the critical influence of surface-mediated interactions on the adsorption process. Surface distortion and coordination effects are found to strongly depend on the coverage and adsorption geometry: the effect of surface distortion dominates when adsorbates reside two or more Pt atoms apart; the effect of surface coordination dominates if hydrogen is adsorbed on neighboring adsorption sites. The above effects are considerably less pronounced on Pt(100) and Pt(110), therefore resulting in weaker interactions between Hads on these two surfaces. Overall, the study highlights the relevance of surface-mediated effects on adsorbate-adsorbate interactions, such as the often-overlooked surface distortion. The effect of these interactions on the hotly debated adsorption site for the adsorbed hydrogen intermediate in the hydrogen evolution reaction is also discussed.

Sensitivity of sub-annual grey pine (Pinus sabiniana) stem growth to water supply and demand in central California

Pinus sabiniana (grey pine) is a common associate of Quercus douglasii (blue oak) in the iconic, ecologically-rich, and economically-relevant Mediterranean woodland savannah of California, USA. While there are dozens of Q. douglasii sites in the International Tree-Ring Data Bank, P. sabiniana was conspicuously absent, and little is known about its growth patterns or water relations. Here, we introduce a new tree-ring chronology of P. sabiniana collected in central California and assess climatic drivers of annual and sub-annual growth. Specifically, we examine earlywood, latewood, and total annual ring widths and analyse their relationships with variables related to water supply (precipitation, soil moisture) and water demand (air temperature, potential evaporation rate). Annual and earlywood widths had nearly identical responses to climate, likely because annual widths mostly consisted of earlywood (mean: 88 %). In both cases, growth was strongly and positively associated with water supply and negatively associated with water demand. Soil moisture was, by far, the strongest and most temporally-consistent correlate of P. sabiniana growth: correlations between soil moisture and annual growth were >0.8 for five contiguous 3-month seasons. Other variables were significant, in part, because of their influence on soil moisture. The association between latewood growth and climate was qualitatively similar but weaker and, with the exception of soil moisture, more seasonally localised (precipitation was relevant in winter and early spring and water demand variables were relevant in summer, somewhat later in the season than for total ring width and earlywood). Further, P. sabiniana growth was nearly always more sensitive to soil moisture than growth of either co-located Q. douglasii or P. ponderosa (ponderosa pine) at a neighbouring site, suggesting that it may act as a particularly sensitive harbinger of drought stress in this ecosystem.

Amino-Induced Modulation of Electronic State and Neighboring Site Distance through Second Shell Boosted Catecholase-Mimicking Activity of Electron-Rich Cu Center.

Boosting the biomimetic catalytic activity of nanozyme is important for its potential application. One common strategy to achieve this goal mainly focused on manipulating the electronic state of metal site through the first coordination shell to modulate the adsorption/desorption strength of related reactant, intermediate and/or product, but remained challenging. Taking Cu-based catecholase-mimicking nanozyme for example, this work herein reports a different strategy involving amino-induced modulation of electronic state through the second shell to raise the electron density of Cu site, which further triggers the repulsion effect between neighboring geminal Cu centers to increase the Cu─Cu distance. The resulting nanozyme with electron-rich Cu site (DT-Cu) presents a lower work function and an upshifted d-band center in comparison with its counterpart (i.e., relatively electron-deficient TA-Cu), which promotes the electron transfer and enhances the adsorption strengths of Cu site for O2, catechol and H2O2 intermediate. The longer Cu─Cu distance of DT-Cu accelerated the O─O bond dissociation of H2O2 intermediate. This expedites the oxygen reduction process during catecholase-like catalysis, which together with the enhanced O2/H2O2/catechol adsorption corporately boosts the catecholase-like activity of DT-Cu.

The Conundrum of "Pair Sites" in Langmuir-Hinshelwood Reaction Kinetics in Heterogeneous Catalysis.

Understanding reaction kinetics is crucial for designing and applying heterogeneous catalytic processes in chemical and energy conversion. Here, we revisit the Langmuir-Hinshelwood (L-H) kinetic model for bimolecular surface reactions, originally formulated for metal catalysts, assuming immobile adsorbates on neighboring pair sites, with the rate varying linearly with the density of surface sites (sites per unit area); r ∝ [*]o 1. Supported metal oxide catalysts, however, offer systematic control over [*]o through variation of the active two-dimensional metal oxide loading in the submonolayer region. Various reactions catalyzed by supported metal oxides are analyzed, such as supported VO x catalysts, including methanol oxidation, oxidative dehydrogenation of propane and ethane, SO2 oxidation to SO3, propene oxidation to acrolein, n-butane oxidation to maleic anhydride, and selective catalytic reduction of nitric oxide with ammonia. The analysis reveals diverse dependencies of reaction rate on [*]o for these surface reactions, with r ∝ [*]o n , where n equals 1 for reactions with a unimolecular rate-determining step and 2 for those with a bimolecular rate-limiting step or exchange of more than 2 electrons. We propose refraining from a priori assumptions about the nature and density of surface sites or adsorbate behavior, advocating instead for data-driven elucidation of kinetics based on the density of surface sites, adsorbate coverage, etc. Additionally, recent studies on catalytic surface mechanisms have shed light on nonadjacent catalytic sites catalyzing surface reactions in contrast to the traditional requirement of adjacent/pair sites. These findings underscore the need for a more nuanced approach in modeling heterogeneous catalysis, especially supported metal oxide catalysts, encouraging reliance on experimental data over idealized assumptions that are often difficult to justify.

Coupled ESR and U-series dating of the northernmost evidence of Gigantopithecus from Jianshi Longgudong site, China

Gigantopithecus was a great ape once lived in Southeast Asia and China during the Pleistocene, and the northernmost evidence of its presence is presently known from the Longgupo and Jianshi Longgudong sites located in the West-Hubei and Three Gorges region in Southof China. Here, we report the first radiometric dating by ESR/U-series method on mammalian teeth of Jianshi Longgudong site which was found in 1970s, and renowned by the discovery of both possible hominin and Gigantopithecus fossils in association with undoubted stone artifacts. As the cave site was completely emptied by the successive excavations, the analyzed teeth were selected from museum collections while the dosimetry was established from reworked sediments sampled on the site. The results obtained on two fossil teeth from the lower layer 8 give a weighted mean age of 1512 ± 94 ka, while a mean age of 1044 ± 53 ka was obtained for two other teeth from the upper layer 4. These ESR/U-series dating results, in agreement with the fauna record, are younger than the previous paleomagnetic dating interpretation and suggest that Jianshi Longgudong sequence is younger than the Olduvai subchron and the neighboring Longgupo site dated by the same methods to ca 2.2–2.5 Ma.

Percolation in random sequential adsorption of lattice animals on a three-dimensional cubic lattice

Percolation properties of the Random Sequential Adsorption (RSA) of objects of various shapes on simple three-dimensional (3D) cubic lattice are studied numerically by means of Monte Carlo simulations. Depositing objects are “lattice animals”, made of a certain number of nearest neighbor sites on a lattice. The aim of this work is to investigate the impact of the geometrical properties of the shapes on the values of percolation threshold θp∗. We analyzed all lattice animals of size n⩽5.Thanks to an extensive database of studied objects, we found that the number of nearest neighbors N1 and the radius of gyration Rg of the objects are correlated with the values of percolation threshold θp∗. For lattice animals of the same size, the percolation threshold θp∗ decreases with an increase in the number of the object’s nearest neighbors N1. If objects of the same size n have the same number of nearest neighbors N1, their percolation threshold θp∗ decreases with an increase in the radius of gyration Rg.

Caught in the Act of Substitution: Interadsorbate Effects on an Atomically Precise Fe/Co/Se Nanocluster.

Directing groups guide substitution patterns in organic synthetic schemes, but little is known about pathways to control reactivity patterns, such as regioselectivity, in complex inorganic systems such as bioinorganic cofactors or extended surfaces. Interadsorbate effects are known to encode surface reactivity patterns in inorganic materials, modulating the location and binding strength of ligands. However, owing to limited experimental resolution into complex inorganic structures, there is little opportunity to resolve these effects on the atomic scale. Here, we utilize an atomically precise Fe/Co/Se nanocluster platform, [Fe3(L)2Co6Se8L'6]+ ([1(L)2]+; L = CN t Bu, THF; L' = Ph2PN(-)Tol), in which allosteric interadsorbate effects give rise to pronounced site-differentiation. Using a combination of spectroscopic techniques and single-crystal X-ray diffractometry, we discover that coordination of THF at the ligand-free Fe site in [1(CN t Bu)2]+ sets off a domino effect wherein allosteric through-cluster interactions promote the regioselective dissociation of CN t Bu at a neighboring Fe site. Computational analysis reveals that this active site correlation is a result of delocalized Fe···Se···Co···Se covalent interactions that intertwine edge sites on the same cluster face. This study provides an unprecedented atom-scale glimpse into how interfacial metal-support interactions mediate a collective and regiospecific path for substrate exchange across multiple active sites.

Suzuki segregation behavior and mechanism in a Co–Cr–Fe–Ni–Mo high-entropy alloy

The knowledge of the Suzuki effect in compositionally complex CoNiCrMo and CoCrFeNiMo solid-solution alloys is rather limited. In this study, the enrichment of Co and Mo atoms and depletion of Cr, Fe, and Ni atoms were determined within the region of four atomic layers at stacking faults (SFs) in a typical quinary concentrated solid-solution alloy (Co0.95Cr0.8Fe0.25Ni1.8Mo0.475) by using scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. To better understand the Suzuki effect, two-stage first-principles Monte Carlo (MC) simulations each with up to 3000 trial swap steps were performed. First, the simulation results suggested the strong tendency of Mo segregation at the second nearest neighbor (2NN) sites at SFs. Nonetheless, as a further Mo segregation induces the excessively large lattice distortion and intrinsic strain energy, it would be inhibited. It was deemed one potential reason for the finite Mo segregation. Second, the simulations revealed the origin and formation of co-segregation of Co and Mo atoms. The segregated Mo atoms at the 2NN sites attract Co atoms, forming the local D019-type ordering at SFs. As a consequence, the stacking fault energy can reach a strongly negative value below −500 mJ/m2. Meanwhile, the Co/Mo co-segregated SFs have high stability against phase transitions to intermetallics and martensite at 773 K.

In Operando X-ray Spectroscopic and DFT Studies Revealing Improved H2 Evolution by the Synergistic Ni-Co Electron Effect in the Alkaline Condition.

The different electrolyte conditions, e.g., pH value, for driving efficient HER and OER are one of the major issues hindering the aim for electrocatalytic water splitting in a high efficiency. In this regard, seeking durable and active HER electrocatalysts to align the alkaline conditions of the OER is a promising solution. However, the success in this strategy will depend on a fundamental understanding about the HER mechanism at the atomic scale. In this work, we have provided thorough understanding for the electrochemical HER mechanisms in KOH over Ni- and Co-based hollow pyrite microspheres by in operando X-ray spectroscopies and DFT calculations, including NiS2, CoS2, and Ni0.5Co0.5S2. We discovered that the Ni sites in hollow NiS2 microspheres were very stable and inert, while the Co sites in hollow CoS2 microspheres underwent reduction and generated Co metallic crystal domains under HER. The generation of Co metallic sites would further deactivate H2 evolution due to the large hydrogen desorption free energy (-1.73 eV). In contrast, the neighboring Ni and Co sites in hollow Ni0.5Co0.5S2 microspheres exhibited the electronic interaction to elevate the reactivity of Ni and facilitate the stability of Co without structure or surface degradation. The energy barrier in H2O adsorption/dissociation was only 0.73 eV, followed by 0.06 eV for hydrogen desorption over the Ni0.5Co0.5S2 surface, revealing Ni0.5Co0.5S2 as a HER electrocatalyst with higher durability and activity than NiS2 and CoS2 in the alkaline medium due to the synergy of neighboring Ni and Co sites. We believe that the findings in our work offer a guidance toward future catalyst design.

Combining techno-economic modeling and spatial analysis for heat planning in rural regions: A case study of the Holbæk municipality in Denmark

This study examines the opportunities and challenges related to heat decarbonization in rural municipalities by applying a spatial analysis in combination with techno-economic modeling using TIMES. While the transition to low-carbon heating technologies is progressing in urban areas, this shift is happening more slowly in rural areas, reflecting a difference in decarbonization rate between urban and rural contexts. This study takes the Holbæk Municipality in Denmark as a case to investigate the potential for rural heating systems considering local fuels, excess heat, and investments in different energy infrastructures. The technology options investigated include both individual heating technologies, such as domestic boilers and heat pumps, and district heating. The modeling results demonstrate that use of excess heat from the municipal wastewater treatment plant and the neighboring industrial site for district heating competes with individual heating systems that have heat pumps and biogas-fueled boilers, where the mix depends on the conditions assumed for each technology and the heat demand density. The extent of district heating expansion differs between districts in the municipality, ranging from 14% to 100% depending on the heat demand density and proximity to the current district heating network. The different possibilities for the transition of the heating sector revealed in this work indicate that a successful transition will require both a clear policy for the heating sector and an explicit decarbonization strategy for the industries that can provide excess heat for district heating.