Selective Dealloying Research Articles

The Effect of Cold Work and Irradiation on the Dealloying Behavior of Ni-Cr Alloys in Molten Fluoride Salts

Molten salt nuclear reactor (MSR) environments present several challenges to structural materials, such as corrosion coupled with radiation damage occurring at high homologous temperatures. When a corrosion driving force exists, such as the presence of an oxidizing impurity with a half-cell redox potential higher than those of the alloying elements, selective dealloying of the less noble element (LN) in a multi-component structural alloy can occur [1]. This process can result in interesting corrosion morphologies such as the formation of a relatively uniform penetrating bicontinuous porous structures in grain interiors and penetrating dealloying along grain boundaries. Irradiation can induce solute segregation and/or saturation of non-equilibrium defects that interact with the corrosion front [2]. Currently, it remains uncertain how irradiation damage within an alloy impacts the process of molten salt dealloying, rendering the morphological instability.In this work, the corrosion dealloying behavior of Ni20Cr alloy (wt.%) was studied in molten LiF-NaF-KF (or FLiNaK) salts at 600°C. Ni20Cr alloys were subjected to two different conditions of Ni ion radiation, one carried out at 25°C and the other at 600°C, creating a peak damage depth nearing ~3µm at approximately 60 dpa. As a surrogate for microstructural damage by radiation, a separate set of Ni20Cr alloys were cold-worked to achieve reductions of thickness of 10%, 30%, and 50% which induce lattice defects in the form of dislocations. Additional samples were subjected to the identical potentiostatic holds attempted previously in molten FLiNaK in carefully selected electrochemical potential regimes where only Cr dealloying occurs in FLiNaK [2]. A porous Ni-rich ligament was formed that undergoes coarsening and densification. Electrochemical impedance spectroscopy (EIS) was used to quantify the porous structures. The pre-irradiated then post-corrosion samples were examined by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) techniques to characterize micro and nanoscale changes in structure and composition. Irradiation produced deeper dealloying depths than observed on annealed samples. Furthermore, the roles of dislocation array and grain boundaries dislocation pile ups, which serve as short-circuit paths for outward Cr transport, during the dealloying process, were closely examined. Acknowledgment Research is primarily supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES). This work was performed in the Department of Materials Science and Engineering (DMSE) in the Center for Electrochemical Science and Engineering (CESE) at the University of Virginia. Utilization of the Malvern-Panalytical Empyrean diffractometer was supported by Nanoscale Materials Characterization Facility (NMCF) with National Science Foundation (NSF) under award CHE-2102156. H.C. acknowledges the National Science Foundation Graduate Research Fellowship (GRFP), GRANT#: 1842490.

Monolithic gold saturated on nanoporous gold@mirror template for highly reliable and fast surface-enhanced Raman scattering detection

The primary challenge hindering the broad application of surface-enhanced Raman scattering (SERS) is the variability in substrate performance due to site differences, leading to unstable detection results. Thus, the current work reports the constant potential deposition of gold (Au) nanostructure on a hybrid nanoporous gold (npAu)-Au mirror template to generate highly stable monolithic Au-saturated npAu@Au-mirror substrate. By systematically adjusting electrochemical variables, different sizes, shapes, and nanogaps of Au nanostructure are generated with high-intensity electromagnetic field regions (hot junctions) for enhanced SERS response. The resulting reproducible and enhanced SERS response of the Au-saturated npAu@Au-mirror mainly originates from i) the precise control of potential and accumulation time (−0.3 V and t = 100 s) to generate uniform and symmetric particle size, dispersion, and nanogaps formation through the reduction, nucleation, and growth of Au nanoparticles; ii) free selective dealloying and complete immersion of Au50Ag50 to ensure identical conditions across the alloy surface. The metrics for substrate efficiency were evaluated for reproducibility (n = 100, RSD = 14.22%), signal stability (storage time 25 days and variation in batches and multiple synthesis runs) and enhancements (enhancement factor∼1.3 × 107). The substrate was extended for the rapid and direct malachite green detection in fish samples with a detection limit of 1.7 × 10−9 mol L−1 and good recoveries (96.69 ± 2.18%∼98.51 ± 0.63%). The monolithic Au-saturated npAu@Au-mirror substrate might be implemented for routine analysis of other target types in food safety-related applications.

Nanoporous NiPt alloy by dealloying of amorphous NiZrPt metallic glass for alkaline hydrogen evolution reaction

The development of high-performance and low-cost alkaline hydrogen precipitation catalysts is critical for the large-scale application of hydrogen energy. In this work, the nanoporous alloy catalysts were synthesized by dealloying melt-spun NiZrPt ribbons. The optimal sample after dealloying shows excellent HER performance in alkaline medium, with a small overpotential of 15 mV to deliver 10 mA cm−2 and a low Tafel slope of 20 mV/dec. The material characterization reveals that the incorporation of Ni modulates the electronic structure of Pt. After selective dealloying of Zr and Ni, a Pt-enriched nanoporous structure was formed on the catalyst surface. Meanwhile, the remaining Ni sites acted as synergistic sites to activate the Pt sites, which allowed for better hydrogen adsorption energy and faster kinetics of the catalytic reaction. Besides, the favorable mechanical flexibility of the material makes it potential for self-supporting electrode. This work presents a way to prepare low-Pt efficient catalysts by amorphous alloy dealloying.

Surface activation via selective dealloying of Cu-based metallic glasses for efficient catalytic behavior.

Surface activation is considered to regulate the electronic structures of materials for enhancing catalytic capability. Herein, we report a controllable strategy for constructing three-dimensional micro-nanoporous copper catalysts with high reactivity and activity for the degradation reaction of organic pollutants. Various micro-nanoporous structures and in situ formation processes by chemical selective dealloying of Cu-based metallic glasses are evaluated due to the surface modification. The porous catalysts exhibit superior catalytic performance, attributing to the catalytic mechanisms related to the superior surface activity of nanoscale copper composites and the strong oxidizing capability of activated radicals. These findings will provide a promising synthesis approach for three-dimensional micro-nanoporous catalysts for many chemical reactions.

Hierarchical-heterostructured porous intermetallics in nickel-cobalt-aluminum alloys as efficient electrocatalysts for hydrogen evolution

Extensive researches have unequivocally revealed the remarkable potential of hierarchical porous intermetallic materials within the realms of electrocatalysis and energy materials. Nevertheless, the efficient and cost-effective synthesis of such electrocatalysts remains a challenging task, and the atomic-level mechanisms underlying hydrogen evolutions at active catalytic sites are still insufficiently comprehended. Herein, we report a novel synthesis technique for the hierarchical-heterostructured non-noble Ni-Co-Al intermetallics using spark plasma sintering followed by a selective dealloying process. This approach maximizes the electrochemical active surface area, thereby facilitating highly efficient hydrogen evolution reactions with an impressively low overpotential of only 75 mV at a current density of 10 mA cm−2 and a Tafel slope of 54 mV dec−1. Through operando X-ray absorption fine structure and theoretical calculations, the dynamic evolution process during the hydrogen evolution reaction procedure is investigated and the atomic Ni and Co sites are identified as synergistic catalytic sites. These characteristics render this hierarchical-heterostructured porous intermetallics appealing contenders for electrocatalysts utilized in high-performance large-scale hydrogen generation applications.

Evaluation of Corrosion Behavior of Various Fe- and Ni-Based Alloys in Molten Li2BeF4 (FLiBe)

Reliable performance of structural alloys is essential for the successful implementation of Generation-IV fluoride salt–cooled high-temperature reactors (FHRs). Most FHR designs are considering molten salt (2LiF-BeF2), or FLiBe, as a primary coolant or fuel carrier. The main corrosion mechanism for alloys exposed to molten fluoride salts is the selective dealloying of active alloying elements. Alloy composition has a significant effect on their high-temperature mechanical properties, but also affects their corrosion behavior. Although Hastelloy-N and its variants show good corrosion resistance compared to higher Cr-containing Ni- or Fe-based alloys, the mechanical properties of these alloys degrade quickly at temperatures above ~600°C. Twelve Ni-based or Fe-based alloys were selected due to their high temperature stability or their low Cr alloy composition and tested for their corrosion behavior in FLiBe. The results show that the mode and the extent of alloy degradation by selective dissolution mechanism corelates well with the overall alloy composition, and not just the concentration of active elements. It was found that there was good correlation between weight loss of the tested alloys and the ratio of major active elements (Cr, Mn) to that of the more noble alloying elements (Ni, Mo).

Selective dealloying of chemically disordered Pt-Ni bimetallic nanoparticles for the oxygen reduction reaction.

Changes in electronic and compositional structures of Pt-Ni electrocatalysts with 44% of Ni fraction with repeated chemical dealloying have been studied. By comparing the Pt-enriched surfaces formed using hydroquinone and sulfuric acid as a leaching agent, we found that hydroquinone generated Pt-enriched surfaces exhibit the highest oxygen reduction reaction (ORR) activity after repeating the treatment twice. In particular, it was found that while sulfuric acid causes an uncontrollable dissolution of Ni clusters, the unique selectivity of hydroquinone allows the preferential dissolution of Ni atoms alloyed with Pt. Despite its wide usage in the field, the results show that traditional acid leaching is unsuitable for Pt-Ni alloys with a high Ni content and an incomplete alloying level. We finally proved that the unique and lasting selectivity of hydroquinone enables an incompletely alloyed Pt-Ni catalyst to obtain a highly ORR active Pt shell region without an extensive loss of Ni.

Biodegradable open-porous scaffolds made of sintered magnesium W4 and WZ21 short fibres show biocompatibility in vitro and in long-term in vivo evaluation

Open-porous scaffolds made of W4 and WZ21 fibres were evaluated to analyse their potential as an implant material. WZ21 scaffolds without any surface modification or coating, showed promising mechanical properties which were comparable to the W4 scaffolds tested in previous studies. Eudiometric testing results were dependent on the experimental setup, with corrosion rates differing by a factor of 3. Cytotoxicity testing of WZ21 showed sufficient cytocompatibility. The corrosion behavior of the WZ21 scaffolds in different cell culture media are indicating a selective dealloying of elements from the magnesium scaffold by different solutions. Long term in-vivo studies were using 24 W4 scaffolds and 12 WZ21 scaffolds, both implanted in rabbit femoral condyles. The condyles and important inner organs were explanted after 6, 12 and 24 weeks and analyzed. The in-vivo corrosion rate of the WZ21 scaffolds calculated by microCT-based volume loss was up to 49 times slower than the in-vitro corrosion rate based on weight loss. Intramembranous bone formation within the scaffolds of both alloys was revealed, however a low corrosion rate and formation of gas cavities at initial time points were also detected. No systemic or local toxicity could be observed. Investigations by μ-XRF did not reveal accumulation of yttrium in the neighboring tissue. In summary, the magnesium scaffold´s performance is biocompatible, but would benefit from a surface modification, such as a coating to obtain lower the initial corrosion rates, and hereby establish a promising open-porous implant material for load-bearing applications. Statement of significanceMagnesium is an ideal temporary implant material for non-load bearing applications like bigger bone defects, since it degrades in the body over time. Here we developed and tested in vitro and in a rabbit model in vivo degradable open porous scaffolds made of sintered magnesium W4 and WZ21 short fibres. These scaffolds allow the ingrowth of cells and blood vessels to promote bone healing and regeneration. Both fibre types showed in vitro sufficient cytocompatibility and proliferation rates and in vivo, no systemic toxicity could be detected. At the implantation site, intramembranous bone formation accompanied by ingrowth of supplying blood vessels within the scaffolds of both alloys could be detected.

Electrochemical Filling of Nanoporous Gold with Silver via Surface-Limited Redox Replacement

Nanoporous (np) metals feature a unique network of interconnected pores and ligaments structured at a length scale of a few to hundreds of nanometers. As a result, np metals have an inherently higher surface area-to-volume ratio resulting in lower melting temperature compared to their bulk metal counterparts. Most applications of np metals have been associated with electrocatalysis. However, in recent years, a growing interest in the use of np metals in microelectronics have been pursued. Among these applications is the development of np-Cu-based chip-to-substrate interconnections that is achieved by Cu-on-Cu bonding. np-Cu is an ideal candidate for solder alternatives because of its relatively lower melting and sintering temperatures. Furthermore, the incorporation of a thin film of Sn in the pores and/or the surface of the np-Cu ligaments could further lower its sintering temperature while maintaining low resistivity. In order to fabricate these composites, there must be strict control over the uniform and flat deposition of the Sn thin film on np-Cu.Here we present a proof-of-concept study on the development of an all-electrochemical metal-filling of np structures. Conventional methods like electron beam induced deposition and overpotential deposition (OPD) have been developed for the filling of porous structure. However, these approaches showed only partial filling that are also accompanied by the growth of three-dimensional protrusions forming outside of the pores. In order to overcome these complications, we developed an approach based on electrochemical atomic layer deposition by surface-limited redox replacement (SLRR). This method allows for a layer-by-layer deposition of metals that has been shown to form relatively flat and uniform deposits. In this study, the model porous structure is np-Au, which is prepared by the selective de-alloying of pre-deposited Au-Cu alloys. The np-Au structure was then filled with Ag via SLRR (in a one-cell configuration) that is realized by successive cycles of the adsorption of a Pb monolayer, serving as a sacrificial metal, that is immediately replaced by Ag via electroless galvanic displacement.A comparative study suggests that the SLRR approach results in a more uniform Ag-filling compared to a stepwise potentiostatic OPD approach that was also done independently. Morphological characterization via surface and cross-sectional scanning electron microscopy (SEM) reveals progressive filling of np-Au with Ag. Additionally, electrochemical BET characterization via cyclic voltammetry of Pb-underpotential deposition (Pb-UPD) was also used to monitor the filling process by measuring the electrochemical surface area of the Ag-filled np-Au composite. The findings from this study will be discussed in detail. Reference:Castillo, Y. Xie, and N. Dimitrov “Filling in nanoporous gold with silver via bulk deposition and surface-limited redox replacement approaches” Electrochimica Acta, 2021, 380, 138196.

Self-organizing Ag-decorated nanoporous Cu by dealloying process

The importance of copper-silver boundaries to produce alcohols or other high value products in CO2 reduction reaction has been reported recently, but the details of the copper and silver arrangement in catalytic applications has yet to be revealed clearly. In this work, we demonstrated experimental evidences of migration by transmission electron microscope (TEM) images during dealloying process and after 2 h of CO2 reduction reaction in Ag-decorated nanoporous Cu. In conclusion, the copper and silver from the trinary alloy Cu-Ag-Al would rearrange themselves into nanoporous structure of copper-core decorated with silver after selective dealloying of Al for 15 min, while copper will move to the surface of nanoporous structure after 2 h of CO2 reduction reaction. This work shows a useful assumption of copper and silver migration during the dealloying process and after CO2 reduction reaction in atomic scale, which can provide details of the synthesis of nanoporous Cu-Ag electrocatalysts

Self-catalytic growth of one-dimensional materials within dislocations in gold

Dislocations in metals affect their properties on the macro- and the microscales. For example, they increase a metal's hardness and strength. Dislocation outcrops exist on the surfaces of such metals, and atoms in the proximity of these outcrops are more loosely bonded, facilitating local chemical corrosion and reactivity. In this study, we present a unique autocatalytic mechanism by which a system of inorganic semiconducting gold(I) cyanide nanowires forms within preexisting dislocation lines in a plastically deformed Au-Ag alloy. The formation occurs during the classical selective dealloying process that forms nanoporous Au. Nucleation of the nanowire originates at the surfaces of the catalytic dislocation outcrops. The nanowires are single crystals that spontaneously undergo layer-by-layer one-dimensional growth. The continuous growth of nanowires is achieved when the dislocation density exceeds a critical value evaluated on the basis of a kinetic model that we developed.

Facile synthesis of MnO2-Cu composite electrode for high performance supercapacitor

Here, we report a facile approach for the development of unique nanoporous MnO2-Cu architecture through a combination of severe surface deformation and dealloying. The severe surface deformation of Cu-Mn alloy prior to selective dealloying resulted in the precipitation of nanoporous MnO2 in the Cu-rich substrate. The in situ grown nanoporous MnO2-Cu architecture demonstrated an areal capacitance of 2.8 F/cm2 at a current density of 5 mA/cm2 and exhibits an excellent cyclic stability of 95% retention for 4000 cycles at 15 mA/cm2 current density. The MnO2-Cu composite structure showed small charge transport resistance of 1.9 Ω as determined using impedance spectroscopy. The asymmetric supercapacitor fabricated using nanoporous MnO2-Cu as anode and reduced graphene oxide as cathode delivers specific energy of 5.55 Wh kg−1 at a specific power of 249.75 W kg−1. The superior performance of nanoporous MnO2-Cu architecture was attributed to its unique microstructure that ensures high surface area, small internal resistance with rapid charge transport. The current approach can be applied to different material systems and is potentially transformative in the emerging field of advanced supercapacitors.

High performance CuO@brass supercapacitor electrodes through surface activation

The 3-dimensional hierarchical nano-porous copper oxide structure developed using thermo-mechanical processing and selective dealloying demonstrated excellent performance as a supercapacitor electrode.

One-step mild fabrication of branch-like multimodal porous Si/Zn composites as high performance anodes for Li-ion batteries

Multimodal porous Si/Zn composites with controllable components and large porosity are conveniently fabricated through one-step selective dealloying of SiZnAl precursor alloys under green and safe conditions. The as-made Si/Zn composites possess open interconnected three-dimensional (3D) network structure with multiscale pore distributions from scores of nanometer to micro scale. Nanoporous (NP) Si/Zn composites exhibit superior reversible capacity, high rate performance, as well as outstanding cycling stability in virtues of 3D interlinked nanoscale scaffold, massive pore openings, and highly conductive Zn dispersoid. The lithium storage performances of as-made anodes follow the order of Si80Zn20 > Si85Zn15 > Si75Zn25 > Si. The optimal NP-Si80Zn20 delivers the high reversible capacity of 901.8 mAh g−1 at 1000 mA g−1 after continuous cycles as long as 1000 loops. Moreover, the full cell assembling with LiFePO4 cathode and NP-Si80Zn20 anode exhibits a large initial coulombic efficiency of 88.9% and respectable cycling stability. With the merits of excellent energy storage performances as well as green and simple preparation, NP-Si/Zn composite as the promising candidate presents attractive application value for lithium ion batteries.

Nickel Foam‐Supported Amorphous FeCo(Mn)−O Nanoclusters with Abundant Oxygen Vacancies through Selective Dealloying for Efficient Electrocatalytic Oxygen Evolution

AbstractDeveloping earth‐abundant, cost‐effective and high‐performance electrocatalyst towards the oxygen evolution reaction (OER) is a great challenge for large‐scale hydrogen production from electrochemical water splitting. Nickel‐foam‐supported amorphous hierarchical nanoclusters of metal/metal (hydr)oxides with abundant oxygen defects (FeCo(Mn)−O/NF) were prepared from an FeCoMn/NF precursor through chemical dealloying. The FeCo(Mn)−O/NF electrode exhibits enhanced OER activity in alkaline electrolyte with an overpotential of only 235 mV to drive a current density of 10 mA cm−2, a small Tafel slope of 44.5 mV dec−1 and excellent durability over 100 h. The superior OER performance is attributed to the synergistic effect of abundant oxygen vacancies, hierarchical morphology and amorphous structure, which essentially modulate the electronic structures and create more active sites. These interesting findings highlight the significance of dealloying strategy on the structural defects and improved catalytic performance of the electrocatalysts.

Inducing surface nanoporosity on Fe-based metallic glass matrix composites by selective dealloying

Nanoporosity (i.e. nanohole formation) is induced at the surface of Fe-based metallic glass matrix composites by selective chemical or electrochemical (at 1 V) etching of a Fe65Cu10Zr10B15 composite material using a 0.065 M HNO3 aqueous electrolyte. While electrochemical treatments are found to remove the Cu-rich precipitates present at the surface of this alloy, chemical etching (in absence of applied potential) only causes partial dissolution of the Fe-rich amorphous matrix. In both cases, the resulting pores exhibit random shapes and their lateral size ranges from a few tens to hundreds of nm. The investigated material is ferromagnetic at room temperature, both before and after dealloying and it does not crystallize during the (electro)chemical etching process. The contact angle in deionized water decreases in the dealloyed states in comparison with the as-spun ribbon. This procedure is appealing for applications that could benefit from the combination of increased surface area and the amorphous character (lack of crystallinity) at the surface of dealloyed metallic glass composite materials.

(Invited) Using Nanoporous and Nanostructured Materials to Improve Fast Charging and High Capacity Battery Materials

In this talk, we examine ways that solution processed nanostructured materials can be used to address both fundamental and practical issues relevant to next generation electrochemical energy storage. Materials with appropriate porous architectures can be synthesized using a range of solution phase methods, including polymer templating, nanoparticle assembly, and selective dealloying of mixed metal precursors. We begin with nanoporous materials for application in fast charging energy storage systems referred to as pseudocapacitors. Here the goal is both to produce practical new fast charging material, as well as to define the nature of pseudocapacitance in nanostructured materials and to establishing design rules for synthesizing future generations of high rate capability materials. We find that in optimized nanoporous materials, the nanoscale structure and porosity can produce a very desirable combination of electrical connectivity, electrolyte access to the interior of the material, ample surface redox sites, and very short solid-state diffusion lengths for lithium ions, all of which facilitate fast charge and discharge. Perhaps more importantly, many nanoscale materials appear to show suppression of the intercalation induced phase transitions that can cause kinetic limitations in bulk materials. The result is a new family of fast charging nanostructured energy storage materials. In this talk, we will specifically explore anode materials based on nanoporous MoS2, MoO2, and Nb2O5, and nanoporous cathode materials based on LiMn2O4 (LMO) and LiVPO4F (LVPF). A combination of electrochemical kinetics and operando X-ray diffraction allows us to correlate nanometer scale architecture, the speed of charge and discharge, and the presence or absence of intercalation induced phase transitions to show that an optimize nanoporous structure is the key to producing new fast charging energy storage materials. Similar porous architectures can also be used to increase stability and cycle life in high capacity alloy-type anode materials that are being considered as replacements for graphite in traditional lithium ion batteries. Unfortunately, alloy-type anodes suffer from short lifetimes due to large volume changes during lithiation or sodiation. One solution is to use nanoscale porosity to help accommodate those large volume changes. Here we specifically focus on nanoporous Sn and nanoporous SbSn, both of which are synthesized by selective etching, and both of which can be alloyed with either lithium or sodium to produce very high capacity anodes. Using transmission X-ray microscopy (TXM), we are able to directly image changes in both individual grains, and in the pore structure itself upon cycling. We find that porous materials expand much less than bulk materials, because the pores help accommodate the strain. More importantly, we find that porous alloys like nanoporous SbSn are more stable than pure metals because the two components, which alloy at different potentials, help stabilize the pores system so that the alloy can expand into the pores with causing them to break or fracture. This results in significantly improved cycle stability. Taken together, these two families of materials emphasize the key role that can be played by nanoscale porosity in optimizing the properties of next generation energy storage materials. References K. Lesel, J.B. Cook, Y. Yan, T.C. Lin, S.H. Tolbert, “Using Nanoscale Domain Size to Control Charge Storage Kinetics in Pseudocapacitive Nanoporous LiMn2O4 Powders.” ACS Energy Lett. 2017, 2, 2293-2298.B. Cook, T.C. Lin, E. Detsi, J. Nelson Weker, S.H. Tolbert “Using X-ray Microscopy To Understand How Nanoporous Materials Can Be Used To Reduce The Large Volume Change In Alloy Anodes.” Nano Lett., 2017, 17, 870−877.B. Cook, E. Detsi, Y. Liu, Y.-L. Liang, H.-S. Kim, X. Petrissans, B. Dunn, S.H. Tolbert, “Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode.” ACS Appl. Mater. Interfaces, 2017, 9, 293−303.B. Cook, H.-S. Kim, T.C. Lin, C.-H. Lai, B. Dunn, S.H. Tolbert, “Pseudocapacitive Charge Storage in Thick Composite MoS2 Nanocrystal Based Electrodes. Adv. Energy Mater. 2016, 1601283.

Easy preparation of nanoporous Ge/Cu3Ge composite and its high performances towards lithium storage

Nanoporous Ge/Cu3Ge composite is fabricated simply through selective dealloying of GeCuAl precursor alloy in dilute alkaline solution. The as-made Ge/Cu3Ge is characterized by three dimensional (3D) bicontinuous network nanostructure which comprises of substantial nanoscale pore voids and ligaments. Owing to the 3D porous architecture and the introduction of well-conductive Cu3Ge, the lithium storage performances of Ge are dramatically enhanced in terms of higher cycling stability and superior rate performance. Nanoporous Ge/Cu3Ge anode delivers steady capacities above 1000 mA h g−1 upon cycling for 70 loops at 400 mA g−1. In particular, after 300 cycles at the high rate of 3200 mA g−1 the capacity retention for Ge/Cu3Ge is able to reach a maximum of 99.3%. On the contrary, the pure nanoporous Ge encounters severe capacity decay. In view of the outstanding energy storage performances and easy preparation, nanoporous Ge/Cu3Ge exhibits great application potential as an advanced anode in lithium storage related technologies.

One-step mild fabrication of porous core-shelled Si@TiO2 nanocomposite as high performance anode for Li-ion batteries

Nanoporous Si@TiO2 composites with the unique core-shell architecture are conveniently fabricated through one-step selective dealloying of SiTiAl ternary alloy under mild conditions. The as-prepared composites consist of bimodal Si network skeleton as the core and interconnected TiO2 nanosponge layer as the shell uniformly distribute on the Si surface to form the porous core-shelled structure. The nanoporous TiO2 as the outer protective layer not only reduce the violent volume change of electrode materials for stable cycling performance but also shorten the diffusion distance of Li+ for high rate capacities. The inner bimodal porous Si possesses an open bicontinuous network structure that can provide the enough empty space and robust backbone to relax the volume variation of composite and guarantee the sufficient electrode-electrolyte contact area. As a result, the optimized nanoporous Si@TiO2 composite delivers the reversible capacity of 1338.1 and 1174.4 mA h g−1 at the current densities of 200 and 1000 mA g−1 after continuous tests for 120 and 100 cycles, respectively. With the advantages of easy preparation, unique architecture, and high lithium storage performances, the porous core-shelled Si@TiO2 composites demonstrate the promising application potential as an anode material for LIBs.

Pulsed Electrodeposition of Highly Porous Pt Alloys for use in Methanol, Formic Acid, and Glucose Fuel Cells

AbstractWe demonstrate an electrodeposition process for the fabrication of highly porous PtCu alloy anodes. In the fabrication process, Pt and different amounts of a second noble metal (Pd, Ru, Au) are repeatedly co‐deposited with Cu from an aqueous electrolyte, followed by selective dealloying of Cu. In this way, highly porous PtCu alloys with roughness factors ranging from 400 to 4000 can be obtained. In all cases, both noble‐metal partners are present on the electrode surface, whereas the majority of copper is likely buried underneath. In addition, we can show that H desorption and CO stripping yield substantially different roughness factors, even when applied to PtCu anodes. Hence, when using or comparing results from different stripping methods, a calibration is required. Compared to PtCu anodes, small additions of Ru (ca. 3 at% Ru) lead to significantly enhanced catalytic activity for the electro‐oxidation of formic acid and methanol, whereas Au‐rich PtCu−Au alloys (ca. 75 at% Au) exhibit significantly improved electrocatalytic activity for glucose oxidation. In some cases, large variations impede the identification of significant differences in electrocatalytic activity. To reduce process variability and to increase the specific surface area, further optimization of the fabrication process is required. Similarly, the deposition of defined alloy compositions will require further investigation, as the composition of electrolyte and deposited alloy do not directly correspond.