Activating Ru in the pyramidal sites of Ru_(2)P-type structures with earth-abundant transition metals for achieving extremely high HER activity while minimizing noble metal content

Rational design of efficient pH-universal hydrogen evolution reaction catalysts to enable large-scale hydrogen production via electrochemical water splitting is of great significance,yet a challenging task.Herein,Ru atoms in the Ru_(2)P structure were replaced with M=Co,Ni,or Mo to produce M_(2-x)Ru_(x)P nanocrystals.The metals show strong site preference,with Co and Ni occupying the tetrahedral sites and Ru the square pyramidal sites of the CoRuP and NiRuP Ru_(2)P-type structures.The presence of Co or Ni in the tetrahedral sites leads to charge redistribution for Ru and,according to density functional theory calculations,a significant increase in the Ru d-band centers.As a result,the intrinsic activity of CoRuP and NiRuP increases considerably compared to Ru_(2)P in both acidic and alkaline media.The effect is not observed for MoRuP,in which Mo prefers to occupy the pyramidal sites.In particular,CoRuP shows state-of-the-art activity,outperforming Ru_(2)P with Pt-like activity in 0.5 M H_(2)SO_(4)(η10=12.3 mV;η100=52 mV;turnover frequency(TOF)=4.7 s^(-1)).It remains extraordinarily active in alkaline conditions(η10=12.9 mV;η100=43.5 mV)with a TOF of 4.5 s^(-1),which is 4x higher than that of Ru_(2)P and 10x that of Pt/C.Further increase in the Co content does not lead to drastic loss of activity,especially in alkaline medium,where,for example,the TOF of Co_(1.9)Ru_(0.1)P remains comparable to that of Ru_(2)P and higher than that of Pt/C,highlighting the viability of the adopted approach to prepare cost-efficient catalysts.

Electrochemical Realization of 3D Interconnected MoS_(3)/PPy Nanowire Frameworks as Sulfur-Equivalent Cathode Materials for Li-S Batteries

The development of freestanding and binder-free electrode is an effective approach to perform the inherent capacity of active materials and promote the mechanism study by minimizing the interference from additives.Herein,we construct a freestanding cathode composed of MoS_(3)/PPy nanowires(NWs)deposited on porous nickel foam(NF)(MoS_(3)/PPy/NF)through electrochemical methods,which can work efficiently as sulfur-equivalent cathode material for Li-S batteries.The structural stability of the MoS_(3)/PPy/NF cathode is greatly enhanced due to its significant tolerance to the volume expansion of MoS_(3)during the lithiation process,which we ascribe to the flexible 3D framework of PPy NWs,leading to superior cycling performance compared to the bulk-MoS_(3)/NF reference.Eliminating the interference of binder and carbon additives,the evolution of the chemical and electronic structure of Mo and S species during the discharge/charge was studied by X-ray absorption near-edge spectroscopy(XANES).The formation of lithium polysulfides was excluded as the driving cathode reaction mechanism,suggesting the great potential of MoS_(3)as a promising sulfur-equivalent cathode material to evade the shuttle effect for Li-S batteries.The present study successfully demonstrates the importance of structural design of freestanding electrode enhancing the cycling performances and revealing the corresponding mechanisms.

High-Performance 3D Li-B-C-Al Alloy Anode and its Twofold Li Electrostripping and Plating Mechanism Revealed by Synchrotron X-Ray Tomography

The uncontrollable Li electrostripping and plating process that results in dendritic Li growth and huge volume change of Li anode limits the practicality of Li metal batteries(LMBs).To simultaneously address these issues,designing three-dimensional(3D),lithiophilic and mechanically robust electrodes seems to be one of the cost-effective strategies.Herein,a new 3D Li-B-C-Al alloy anode is designed and fabricated.The prepared 3D alloy anode exhibits not only superior lithiophilicity that facilitates uniform Li nucleation and growth but also sufficient mechanical stability that maintains its structural integrity.Superior performance of the prepared 3D alloy is demonstrated through comprehensive electrochemical tests.In addition,non-destructive and 3D synchrotron X-ray computed tomography(SX-CT)technique is employed to investigate the underlying working mechanisms of the prepared alloy anode.A unique twofold Li electrostripping and plating mechanism under different electrochemical cycling conditions is revealed.Lastly,improved performance of the full cells built with the 3D alloy anode and LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811)cathode corroborate its potential application capability.Overall,the current work not only showcases the superiority of the 3D alloy as potential anode material for LMBs but also provides fundamental insights into its underlying working mechanisms that may further propel its research and development.

Enhanced Catalytic Activity of Gold@Polydopamine Nanoreactors with Multi-compartment Structure Under NIR Irradiation

Photothermal conversion(PTC)nanostructures have great potential for applications in many fields,and therefore,they have attracted tremendous attention.However,the construction of a PTC nanoreactor with multi-compartment structure to achieve the combination of unique chemical properties and structural feature is still challenging due to the synthetic difficulties.Herein,we designed and synthesized a catalytically active,PTC gold(Au)@polydopamine(PDA)nanoreactor driven by infrared irradiation using assembled PS-b-P2VP nanosphere as soft template.The particles exhibit multi-compartment structure which is revealed by 3D electron tomography characterization technique.They feature permeable shells with tunable shell thickness.Full kinetics for the reduction reaction of 4-nitrophenol has been investigated using these particles as nanoreactors and compared with other reported systems.Notably,a remarkable acceleration of the catalytic reaction upon near-infrared irradiation is demonstrated,which reveals for the first time the importance of the synergistic effect of photothermal conversion and complex inner structure to the kinetics of the catalytic reduction.The ease of synthesis and fresh insights into catalysis will promote a new platform for novel nanoreactor studies.

Carbon materials for stable Li metal anodes: Challenges, solutions, and outlook

Lithium(Li)metal is regarded as the ultimate anode for next-generation Li-ion batteries due to its highest specific capacity and lowest electrochemical potential.However,the Li metal anode has limitations,including virtually infinite volume change,nonuniform Li deposition,and an unstable electrode-electrolyte interface,which lead to rapid capacity degradation and poor cycling stability,significantly hindering its practical application.To address these issues,intensive efforts have been devoted toward accommodating and guiding Li deposition as well as stabilizing the interface using various carbon materials,which have demonstrated excellent effectiveness,benefiting from their vast variety and excellent tunability of the structure-property relationship.This review is intended as a guide through the fundamental challenges of Li metal anodes to the corresponding solutions utilizing carbon materials.The specific functionalities and mechanisms of carbon materials for stabilizing Li metal anodes in these solutions are discussed in detail.Apart from the stabilization of the Li metal anode in liquid electrolytes,attention has also been paid to the review of anode-free Li metal batteries and solid-state batteries enabled by strategies based on carbon materials.Furthermore,we have reviewed the unresolved challenges and presented our outlook on the implementation of carbon materials for stabilizing Li metal anodes in practical applications.

Prompt Electrodeposition of Ni Nanodots on Ni Foam to Construct a High-Performance Water-Splitting Electrode:Efficient, Scalable,and Recyclable

In past decades,Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)catalysts for water splitting.With increasing demands for Ni worldwide,simplifying the fabrication process,increasing Ni recycling,and reducing waste are tangible sustainability goals.Here,binder-free,heteroatom-free,and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method.Typically,active Ni nanodot(NiND)clusters are electrodeposited on Ni foam(NF)in Ni(NO3)2 acetonitrile solution.After drying in air,NiO/NiND composites are obtained,leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode.The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials(10ηHER= 119 mV and 50ηOER=360 mV)and can promote water catalysis at 1.70 V@ 10mA cm-2.More importantly,the recovery of raw materials(NF and Ni(NO3)2)is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes.Additionally,a large-sized(S^70 cm2)NiO/NiNDs@NF catalytic electrode with high durability has also been constructed.This method provides a simple and fast technology to construct high-performance,low-cost,and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.

Sodiophilic and conductive carbon cloth guides sodium dendrite-free Na metal electrodeposition

Sodium metal battery(SMB)technology is one of the most promising candidates for next-generation rechargeable energy storage systems due to its high theoretical capacity and economical costeffectiveness.Unfortunately,its practical implementation is hindered by several challenges including short life-span and fast capacity decay,which is closely related to the uncontrollable generation of the sodium dendrites.Herein,a nitrogen and oxygen co-doped three-dimensional carbon cloth with hollow tubular fiber units was constructed as the host material for Na plating(Na@CC)to tackle these challenges.The obtained composite electrode can effectively reduce the nucleation overpotential of Na,guide the homogeneous Na^(+)flux,increase the kinetics of Na electrodeposition,lower the effective current density and eventually suppress the formation of electrochemically inactive Na dendrites.As a result,batteries built with the Na@CC composites exhibited stable long-term cycling stability.To gain an in-depth and comprehensive understanding of such phenomena,non-destructive and three-dimensional synchrotron X-ray tomography was employed to investigate the cycled batteries.Moreover,the COMSOL Multiphysics simulation was further employed to reveal the Na electrodeposition mechanisms.The current work not only showcases the feasibility of currently proposed sodiophilic 3 D Na@CC composite electrode but also provides fundamental insights into the underlying working mechanisms that govern its outstanding electrochemical performance.

Magnetic Phase Diagram of Cu4-xZnx(OH)6FBr Studied by Neutron-Diffraction and μSR Techniques

We systematically investigate the magnetic properties of Cu4-xZnx(OH)6FBr using the neutron diffraction and muon spin rotation and relaxation(μSR) techniques.Neutron-diffraction measurements suggest that the longrange magnetic order and the orthorhombic nuclear structure in the x=0 sample can persist up to x=0.23 and 0.43,respectively.The temperature dependence of the zero-field μSR spectra provides two characteristic temperatures,TA0 and Tλ,which are associated with the initial drop close to zero time and the long-time exponential decay of the muon relaxation,respectively.Comparison between TA0 and TM from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to x=0.82.On the other hand,the doping level where Tλ becomes zero is about 0.66,which is much higher than threshold of the long-range order,i.e.,~0.4.Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above x=0.66 with the perfect kagome planes.

Anomalies in the short-range local environment and atomic diffusion in single crystalline equiatomic CrMnFeCoNi highentropy alloy

Multi-edge extended X-ray absorption fine structure(EXAFS)spectroscopy combined with reverse Monte Carlo(RMC)simulations was used to probe the details of element-specific local coordinations and component-dependent structure relaxations in single crystalline equiatomic CrMnFeCoNi high-entropy alloy as a function of the annealing temperature.Two representative states,namely a high-temperature state,created by annealing at 1373 K,and a low-temperature state,produced by long-term annealing at 993 K,were compared in detail.Specific features identified in atomic configurations of particular principal components indicate variations in the local environment distortions connected to different degrees of compositional disorder at the chosen representative temperatures.The detected changes provide new atomistic insights and correlate with the existence of kinks previously observed in the Arrhenius dependencies of component diffusion rates in the CrMnFeCoNi high-entropy alloy.

Insights into the kinetics–morphology relationship of 1-, 2-, and 3D TiNb_(2)O_(7) anodes for Li-ion storage

Understanding the influence of electrode material’s morphology on electrochemical behavior is of great significance for the development of rechargeable batteries,however,such studies are often limited by the inability to precisely control the morphology of electrode materials.Herein,nanostructured titanium niobium oxides(TiNb_(2)O_(7))with three different morphologies(one-dimensional(1D),two-dimensional(2D),and three-dimensional(3D))were synthesized via a facile microwave-assisted solvothermal method.The influence of the morphological dimension of TiNb_(2)O_(7) as electrode material on the electrochemical performance in Li-ion batteries(LIBs)and the underlying correlation with the electrochemical kinetics were studied in detail.2D TiNb_(2)O_(7)(TNO-2D)shows a superior rate capability and cycling stability,associated with improved kinetics for charge transfer and Li-ion diffusion,compared to the 1D and 3D materials.Operando X-ray diffraction measurements reveal the structural stability and crystallographic evolution of TNO-2D upon lithiation and delithiation and correlate the Li-ion diffusion kinetics with the lattice evolution during battery charge and discharge.Moreover,carbon-coated TNO-2D achieves enhanced rate capability(205 mAh·g^(-1) at 50 C)and long-term cycling stability(87%after 1000 cycles at 5 C).This work provides insights into the rational morphology design of electrode materials for accelerated charge transfer and enhanced fast-charging capability,pushing forward the development of electrode materials for high-power rechargeable batteries in future energy storage.

Anomalous thermal expansion and enhanced magnetocaloric effect in<001>-textured Mn_(x)Fe_(5-x)Si_(3) alloys

The development of zero and negative therma expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were obtained in directionally-solidified Mn_(x)Fe_(5-x)Si_(3)alloys with a strong<001>texture,in striking contrast to positive thermal expansion in their isotropic counterparts Magnetometry and in-situ X-ray diffraction(XRD)measurements were performed to uncover the origin of the anomalous thermal expansion.Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples,where the magnetic moments are aligned within the ab plane of the hexagonal structure Temperature-dependent XRD on the x=1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition.As a result,the macroscopic ZTE(~0.22×10^(-6)K^(-1))in the x=1 sample can be attributed to the microscopic magneto volume effect within the ab plane,which is realized by the introduction of the<001>-textured microstructure.Besides,the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x=1.5 and 2 samples.Additionally,textured x=1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly-oriented grains.Consequently this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.

Recyclable Perovskite Solar Cells with Lead Sulfate Contact

Previous cost analysis of perovskite solar cells(PSCs)has revealed that the transparent conductive oxide(TCO)substrates account for most of the material cost,emphasizing the need to recover TCO in PSC recycling.However,the conventional use of compact and ultrathin electron transport materials(ETMs)such as TiO_(2)and SnO_(2),poses a challenge to their removal from the substrate,hindering effective PSC recycling.Here,PbSO_(4) nanoparticles with(011)surface were used as ETM to fabricate PSCs.The yielded metallicity on the PbSO_(4) nanoparticle surface promoted extracted electron transport across the nanoparticle surface.A certified efficiency as high as 17.9%for the submodule(204.9 cm^(2))with PbSO_(4) was realized successfully,and the best effi-ciency on a small area(0.1 cm^(2))reached 24.1%.The PbSO_(4) layer was removed effortlessly from the substrate by simple aminoethanol washing to recover the TCO,the most expensive component of PSCs.This work provides a novel strategy to prepare soluble insulator-based ETMs by constructing metallic surfaces of nanoparticles;thus,fabricating efficient and recyclable PSCs.

Spin dynamics of the E8 particles

Unlike the classical phase transition driven by thermal fluctuations,the quantum phase transition arises at zero temperature when the system is tuned by a non-thermal parameter[1].For a continuous quantum phase transition,novel physics with higher symmetry may emerge at the quantum critical point(QCP).

Research Article Local structure and magnetic properties of a nanocrystalline Mnrich Cantor alloy thin film down to the atomic scale

The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.

Oxidization-induced structural optimization of Ni_(3)Fe-N-C derived from 3D covalent organic framework for high-efficiency and durable oxygen evolution reaction

NiFe composites have been regarded as promising candidates to replace commercial noble-based electrocatalysts for the oxygen evolution reaction(OER).However,their practical applications still suffer from poor conductivity,limited activity,durability.To address these issues,herein,by utilizing three-dimensional covalent organic framework(3D-COF)with porous confined structures and abundant coordinate N sites as the precursor,the partially oxidized Ni_(3)Fe nanoalloys wrapped by Ndoped carbon(N-C)layers are constructed via simple pyrolysis and subsequent oxidization.Benefiting from the 3D curved hierarchical structure,high-conductivity of Ni_(3)Fe and N-C layers,well-distributed active sites,the as-synthesized O-Ni_(3)Fe-NC catalyst demonstrates excellent activity and durability for catalyzing OER.Experimental and theoretical analyses disclose that both high-temperature oxidization and the OER process greatly promote the formation and exposure of the Ni(Fe)OOH active species as well as lower charge transfer resistance,inducing its optimized OER activity.The robust graphitized N-C layers with superior conductivity and their couplings with oxidized Ni_(3)Fe nanoalloys are beneficial for stabilizing catalytic centers,thereby imparting O-Ni_(3)Fe-N-C with such outstanding stability.This work not only provides a rational guidance for enriching and stabilizing high-activity catalytic sites towards OER but also offers more insights into the structural evolution of NiFe-based OER catalysts.

Defect-density control of platinum-based nanoframes with high-index facets for enhanced electrochemical properties

Structure-engineered platinum-based nanoframes(NFs)at the atomic level can effectively improve the catalytic performance for fuel cells and other heterogeneous catalytic fields.We report herein,a microwave-assisted wet-chemical method for the preparation of platinum-copper-cobalt NFs with tunable defect density and architecture,which exhibit enhanced activity and durability towards the electro-oxidation reactions of methanol(MOR)and formic acid(FAOR).By altering the reduction/capping agents and thus the nucleation/growth kinetics,trimetallic platinum-copper-cobalt hexapod NFs with different density high-index facets are achieved.Especially,the rough hexapod nanoframes(rh-NFs)exhibit excellent specific activities towards MOR and FAOR,7.25 and 5.20 times higher than those of benchmark Pt/C,respectively,along with prolonged durability.The excellent activities of the rh-NFs are assigned to a synergistic effect,including high density of defects and high-index facets,suitable d-band center,and open-framework structure.This synergistic working mechanism opens up a new way for enhancing their electrocatalytic performances by increasing defect density and high-index facets in open-framework platinum-based NFs.

Enhanced reversibility of the magnetoelastic transition in(Mn,Fe)2(P,Si)alloys via minimizing the transition-induced elastic strain energy

Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.

Efficient application of carbon-based nanomaterials for high-performance perovskite solar cells

The power conversion efficiency of perovskite solar cells(PSCs) has rapidly risen from 3.8% to over25.0% in just about one decade, which attracts a lot of attention from the scientific and engineering communities.However, some challenges remain, hindering the progress of commercialization such as intrinsic and extrinsic(environmental) stabilities, which can be improved by an interface and structural engineering. In recent years, some reports indicate that the interfacial engineering using carbon-based nanomaterials additives plays a crucial role in the process of charge carriers and perovskite crystal growth and thereby enhances device performance and operational stability. Here, we review the development of the varieties of carbon-based nanomaterials applications in PSCs, such as hole-transporting layers(HTLs), electron-transporting layers(ETLs), perovskite bulk layer, and their interfaces.Furthermore, we proposed a further suggestion about the optimized preparation conditions for the preparation of PSCs, which may inspire the researcher to discover, design,and manufacture the more efficient perovskite solar cells in academic and industry.

Al-driven peculiarities of local coordination and magnetic properties in single-phase Al_(x)-CrFeCoNi high-entropy alloys

Modern design of superior multi-functional alloys composed of several principal components requires in-depth studies of their local structure for developing desired macroscopic properties.Herein,peculiarities of atomic arrangements on the local scale and electronic states of constituent elements in the single-phase face-centered cubic(fcc)-and body-centered cubic(bcc)-structured high-entropy Alx-CrFeCoNi alloys(x=0.3 and 3,respectively)are explored by element-specific X-ray absorption spectroscopy in hard and soft X-ray energy ranges.Simulations based on the reverse Monte Carlo approach allow to perform a simultaneous fit of extended X-ray absorption fine structure spectra recorded at K absorption edges of each 3d constituent and to reconstruct the local environment within the first coordination shells of absorbers with high precision.The revealed unimodal and bimodal distributions of all five elements are in agreement with structure-dependent magnetic properties of studied alloys probed by magnetometry.A degree of surface atoms oxidation uncovered by soft X-rays suggests different kinetics of oxide formation for each type of constituents and has to be taken into account.X-ray magnetic circular dichroism technique employed at L2,3 absorption edges of transition metals demonstrates reduced magnetic moments of 3d metal constituents in the sub-surface region of in situ cleaned fcc-structured Al0.3-CrFeCoNi compared to their bulk values.Extended to nanostructured versions of multicomponent alloys,such studies would bring new insights related to effects of high entropy mixing on low dimensions.

Characterization and modeling of the temperature-dependent thermal conductivity in sintered porous silicon-aluminum nanomaterials

Nanostructured silicon and silicon-aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering(SPS)of silicon nanopowder,mesoporous silicon(pSi),and aluminum nanopowder.The interplay of metal-assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity.Morphology and temperaturedependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport.Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions.We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples.In contrast,strong grain growth is observed for sintered nanopowders under similar sintering conditions.We observe that aluminum agglomerations induce local grain growth,while aluminum diffusion is observed in porous silicon and dispersed nanoparticles.A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains.With a modified Landauer/Lundstrom approach the relative thermal conductivity and the scattering length are extracted.The relative thermal conductivity confirms the applicability of Kirkpatrick’s effective medium theory.The extracted scattering lengths are in excellent agreement with the harmonic mean of log-normal distributed domain sizes and the interpore distances combined by Matthiessen’s rule.