Nanoporous Pd Research Articles

Effect of the cryogenic treatment on the electrocatalytic performance of the active self-supporting nanoporous Pd–Ag catalyst with high-index facets’ preferred orientation

Effect of the cryogenic treatment on the electrocatalytic performance of the active self-supporting nanoporous Pd–Ag catalyst with high-index facets’ preferred orientation

Hydrogen Evolution Atomic Cluster Catalysts-Decorated Hierarchical Nanoporous Zinc for on-Demand Hydrogen Generation By Metal Hydrolysis

In recent years, there has been an increasing interest in nanoporous metals due to their wide range of applications, including catalysis, electrocatalysis, energy storage, actuation, and plasmonics. However, considerable attention has been given to precious nanoporous metals such as nanoporous Au, Pd, Pt, Ag, and Cu due to their low chemical reactivity, which makes them relatively easy to synthesize and characterize. Less precious nanoporous metals such as nanoporous Zn, Al, and Mg have been rarely fabricated and characterized because of their relatively high chemical reactivity 1. In this talk, I will present a novel, highly scalable approach to making hierarchical nanoporous zinc (NP-Zn) decorated with atomic clusters of hydrogen evolution catalysts for on-demand hydrogen generation by metal hydrolysis. Our approach involves selective etching in combination with galvanic replacement reactions. The conventional selective etching method requires several days to create a monolithic piece of NP-Zn 2. Our approach creates the same amount of hierarchical NP-Zn in less than 5 minutes, instead of several days. In our work, we used focused ion beam/scanning electron microscopy techniques to reveal the internal nanoscale morphology of the hierarchical NP-Zn, and small-angle X-ray scattering to analyze the pore size distribution. In general, when NP-Zn is used for hydrogen generation by metal hydrolysis, the hydrogen generation yield is low, typically around 20%. This is because zinc is naturally a poor hydrogen evolution material. Our process overcomes this issue by creating NP-Zn with its interface decorated with clusters of hydrogen evolution catalysts, which enables hydrogen generation yield exceeding 90% depending on the catalyst loading. References (1) Fu, J.; Welborn, S. S.; Detsi, E. Dealloyed Air- and Water-Sensitive Nanoporous Metals and Metalloids for Emerging Energy Applications. ACS Appl. Energy Mater. 2022, 5 (6), 6516–6544. https://doi.org/10.1021/acsaem.2c00405.(2) Fu, J.; Deng, Z.; Lee, T.; Corsi, J. S.; Wang, Z.; Zhang, D.; Detsi, E. pH-Controlled Dealloying Route to Hierarchical Bulk Nanoporous Zn Derived from Metastable Alloy for Hydrogen Generation by Hydrolysis of Zn in Neutral Water. ACS Appl. Energy Mater. 2018, 1 (7), 3198–3205. https://doi.org/10.1021/acsaem.8b00419.

Designing nanoporous Pd catalyst with dual enhancement of thermodynamics and kinetics for formic acid oxidation reaction

Conventional strategies for developing highly efficient electrocatalysts involve enhancing thermodynamics to minimize overpotential and improving kinetics to maximize reaction current. However, current research on Pd-based catalysts for formic acid oxidation reaction (FAOR) mainly focuses on accelerating its kinetics to increase the peak current. This study proposes a catalyst design that can simultaneously improve the kinetics and thermodynamics of FAOR. Specifically, the home-made catalyst (NPG-Pt1-Pd1) is obtained by sequentially depositing monolayer Pt and Pd shells on the surface of nanoporous gold (NPG) substrate. Compared with commercial Pd/C, this electrocatalyst exhibits a noticeable negative shift in onset potential (∼100 mV) and a significantly improved peak current (∼6 times). Experimental data and theoretical calculations demonstrate that NPG-Pt1-Pd1 exhibits a comparatively suitable adsorption energy for small molecules, not only reducing the overpotential but also accelerating the reaction rate of FAOR. Moreover, when applied in direct formic acid fuel cells (DFAFC), the NPG-Pt1-Pd1 anode with an exceptionally low Pd loading of 8.5 μg cm−2, achieves a remarkable power density of 141 mW cm−2. The power efficiency of Pd is 230 times that of Pd/C (1 mg cm−2, 73 mW cm−2). Therefore, this work provides a new methodology for developing efficient Pd-based FAOR electrocatalysts.

Sonogashira coupling reactions with ligand-free heterogeneous nanoporous Pd catalyst

The Sonogashira coupling reaction is one of the most important protocols for the production of aryl alkynes. In order to solve the problems existing in Sonogashira cross-coupling reaction, according to the application of nanoporous palladium in Suzuki and Heck cross-coupling reactions, nanoporous palladium was used as the sustainable catalyst for the Sonogashira cross-coupling reaction. A sustainable catalyst system was tested and optimized without cuprous ion, phosphine ligand, or amine additives. Nanoporous palladium catalyst remained stable over five cycles without significant leaching or loss of catalytic activity, and the desired alkynes were obtained in high yields.

Potentiostatic Dealloying Fabrication and Electrochemical Actuation Performance of Bulk Nanoporous Palladium

Metallic actuators increasingly exhibit superiority over conventional actuators (such as piezoelectric ceramics) via low energy consumption and large strain amplitude. Large strain amplitude and high strain energy density (or work density) are required for an actuator with excellent comprehensive performance. Herein, we fabricated bulk nanoporous Pd (np-Pd) with a dense nanoporous structure by two-step potentiostatic dealloying of as-annealed Ni–Pd alloy with chemical corrosion resistance, and investigated the dealloying behaviors as well as electrochemical actuation performance. A visible current density oscillation occurred during dealloying, which is related to formation/dissolution of the passivating film. Additionally, since the dense and continuous ligaments establish a good network connectivity for large strain response, the np-Pd achieves a strain amplitude of up to 3.74% and high strain energy density, which stands out among many actuator materials (e.g., np-AuPt, np-Ni, and np-AlNiCu). Our study provides a useful guidance for fabricating metallic actuators with excellent comprehensive performance.

Functionalized silica nanoporous Pd complex for reduction of nitroarenes and dyes

Pd adorned on SBA-Pr-3AP ([email protected]) was investigated as a catalyst for the degradation of natural, synthetic organic dyes, and the reduction of nitroarenes by NaBH4 as a reducing agent with recyclability and regeneration procedure was discerned which may open up new avenues for remediation of aqueous pollutants. The degradation of dangerous dyes such as methylene blue, methyl orange, and natural colors from pomegranate (PM) and opuntia (OP), and the reduction of nitroaromatics at ambient temperature, were studied. The primary materials of numerous medications, agrochemicals, pigments, and colors are anilines, one of the crucial chemical feedstocks. In this perspective, the method for providing aniline derivatives is the catalytic reduction of nitro. An effective catalyst demonstrated to be extremely effective for the reduction of nitroarenes into various amines.

Magnetism of Co-rich clusters embedded in nanoporous Pd prepared by electrochemical dealloying — Influence of thermal annealing

Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature TB of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co–Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of TB occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces TB further down to 35 K. Additionally, a second blocked magnetic phase with much higher TB emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co–Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix.

Nanoporous Cauliflower-like Pd-Loaded Functionalized Carbon Nanotubes as an Enzyme-Free Electrocatalyst for Glucose Sensing at Neutral pH: Mechanism Study.

In this work, we propose a novel functionalized carbon nanotube (f-CNT) supporting nanoporous cauliflower-like Pd nanostructures (PdNS) as an enzyme-free interface for glucose electrooxidation reaction (GOR) in a neutral medium (pH 7.4). The novelty resides in preparing the PdNS/f-CNT biomimetic nanocatalyst using a cost-effective and straightforward method, which consists of drop-casting well-dispersed f-CNTs over the Screen-printed carbon electrode (SPCE) surface, followed by the electrodeposition of PdNS. Several parameters affecting the morphology, structure, and catalytic properties toward the GOR of the PdNS catalyst, such as the PdCl2 precursor concentration and electrodeposition conditions, were investigated during this work. The electrochemical behavior of the PdNS/f-CNT/SPCE toward GOR was investigated through Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), and amperometry. There was also a good correlation between the morphology, structure, and electrocatalytic activity of the PdNS electrocatalyst. Furthermore, the LSV response and potential-pH diagram for the palladium–water system have enabled the proposal for a mechanism of this GOR. The proposed mechanism would be beneficial, as the basis, to achieve the highest catalytic activity by selecting the suitable potential range. Under the optimal conditions, the PdNS/f-CNT/SPCE-based biomimetic sensor presented a wide linear range (1–41 mM) with a sensitivity of 9.3 µA cm−2 mM−1 and a detection limit of 95 µM (S/N = 3) toward glucose at a detection potential of +300 mV vs. a saturated calomel electrode. Furthermore, because of the fascinating features such as fast response, low cost, reusability, and poison-free characteristics, the as-proposed electrocatalyst could be of great interest in both detection systems (glucose sensors) and direct glucose fuel cells.

Operando SQUID Magnetometry for the Characterization of Electrochemical Systems: Charge Transfer in Battery Materials and Electrochemical Dealloying Processes

The combination of magnetism and electrochemistry has attracted considerable attention for application-relevant issues, like the electrodeposition of magnetic thin films or the electrochemically-induced switching of magnetic properties [1,2]. The fact that magnetism variations occurring during electrochemical charging can also serve as diagnostic tool for the corresponding electrochemical processes has been little exploited until now. In this talk, we will demonstrate the capability of operando SQUID magnetometry measurements to characterize electrochemical systems based on two examples: (i) the identification of the electroactive species in Li-ion and Na-ion battery cathodes, (ii) the distinction between different dissolution stages during electrochemical dealloying of Co-Pd alloy.Enabling such operando magnetic studies we have developed a three-electrode electrochemical cell for operation in a commercial state-of-the-art SQUID magnetometer [3].This new cell design allows a precise correlation between the detected variations of the magnetic moment and the electrochemical processes occurring in the investigated sample. Its capability was proven by performing the first in-situ electrodeposition experiments in a SQUID magnetometer [3,4].Applying this new operando technique to (i) Li-ion and Na-ion battery cathodes we could enable a continuous monitoring of the oxidation states of the transition metal ions and therefore an identification of the redox active ions. Our measurements on LiNi0.33Mn0.33Co0.33O2 revealed that first Ni acts as redox active ion and changes its oxidation state stepwise from Ni2+ to Ni3+ and then from Ni3+ to Ni4+. When more than 2/3 of the Li ions are extracted, a simultaneous oxidation of Co3+ and O2- ions takes place that is associated with irreversible capacity losses [5]. Operando magnetic studies on NaV2(PO4)3 cathodes have shown that the vanadium ion is the only ion undergoing oxidation and reduction upon battery operation. However, in the first charging cycle peculiarities in the magnetic susceptibility indicate the occurrence of parasitic side reactions [6].In the case of (ii) in situ dealloying of a Co75Pd25 in a SQUID magnetometer the observed variations of the magnetic moment allowed a distinction between the primary (dissolution of the initial alloy) and secondary (dissolution of residual atoms from porous structure) dealloying steps. The observed transition from alloy ferromagnetism to superparamagnetic behavior, can be ascribed to the formation of Co-rich clusters in the obtained nanoporous Pd framework [7]. Furthermore, the magnetic coupling between these clusters can be reversibly tuned by electrochemical hydrogen intercalation, leading to an On and Off switching of magnetism at room temperature [8].All in all, these two examples prove that operando SQUID magnetometry measurements can serve as a sensitive fingerprint for the processes taking place in various electrochemical systems.Financial support by the Austrian Science Fund (FWF): P30070-N36 is gratefully acknowledged. This work was performed in the framework of the inter-university cooperation of TU Graz and Uni Graz on natural sciences (NAWI Graz).[1] K. Leistner, Curr. Opin. Electrochem. 25 (2021) 100636[2] C. Navarro-Senent et al., APL Mater. 7 (2019) 030701[3] S. Topolovec et al., Rev. Sci. Instrum. 86 (2015) 063903[4] S. Topolovec et al., J. Magn. Magn. Mater. 397 (2016) 96[5] G. Klinser et al., Appl. Phys. Lett. 109 (2016) 213901[6] G. Klinser et al., Phys. Chem. Chem. Phys. 21 (2019) 20151[7] M. Gößler et al., J. Appl. Phys. 128 (2020) 093904[8] M. Gößler et al., Small 15 (2019) 1904523

Metastable Nanoporous Palladium Evolving from Palladium Nanocrystals

AbstractNanoporous metals can be used in many technological applications, and continuous interest has been focused on their preparation. In this study, we describe a different type of preparation method, in which nanoporous palladium (Pd) is prepared from Pd nanocrystals by the elimination of stabilizers. The resulting nanoporous Pd has a bimodal pore structure with an extensive surface area, and its surfaces are electrochemically accessible and exhibit higher catalytic activity toward ethanol electrooxidation than that of the commercial Pd black catalyst. An interesting feature is that the atomic surface structure can be sensitively altered by the preparation temperature and solvent, thereby increasing the catalytic activity of nanoporous Pd. The proposed method is simple and available for mass production and is expected to be a new alternative for producing electrochemically active nanoporous Pd.

Aqueous Formate‐Based Li‐CO2 Battery with Low Charge Overpotential and High Working Voltage

AbstractLi‐CO2 batteries (LCOBs) are considered to be an important strategy toward efficient carbon sequestration and energy storage. However, most typical discharge products (Li2CO3 and C) are insoluble and chemically stable, and require a high charge overpotential (≈3.5–4.5 V) to be decomposed. Herein, a novel aqueous LCOB with formic acid (HCOOH) as the discharge product is proposed. The soluble HCOOH can be directly utilized in the charge process without any further purification or compression, realizing a very facile electrochemical cycle. Nanoporous Pd films with a high electrochemical surface area exhibit a high bifunctional performance toward both CO2 reduction and formic acid oxidation. Accordingly, the assembled LCOB achieves a high working potential plateau of 2.61 V whereas the charge potential is significantly lowered to 2.87 V, delivering the highest energy efficiency of 91%. The present work demonstrates a brand‐new aqueous LCOB with HCOOH as the discharge product for utilizing CO2 as power source.

Facile preparation of surface-oxidized nanoporous Pd for homocoupling reaction

Surface-oxidized nanoporous Pd (SO NP Pd) catalyst was prepared easily from nanoporous Pd, which was dealloyed from a NiPdP glass. 1,3-Diynes were synthesized in high to excellent yields through the homocoupling of terminal acetylenes using SO NP Pd prepared at 250 °C in air. The presence of Pd (II) in the surface-oxidized layer was crucial for the homocoupling reaction of terminal alkynes.

Nanoporous Pd1−xCox for hydrogen-intercalation magneto-ionics

The use of hydrogen atoms for magneto-ionic applications has only been explored recently. Benefits of hydrogen compared to other ionic species for tuning magnetism are high switching speed and large changes in magnetic moment. Here, we test the influence of hydrogen intercalation on magnetism in nanoporous Pd(1−x)Cox, with Co being located in superparamagnetic clusters, building upon a previously suggested material system. Tailoring the Co concentration and distribution allows the magnitude of the magneto-electric effect to be influenced as well as to gain a deeper understanding of the interaction of hydrogen with magnetic clusters. In situ magnetization measurements are conducted to directly observe the variation in magnetic moment upon hydrogen-charging in nanoporous Pd(1−x)Cox. Temperature-dependent magnetization curves show that interstitial hydrogen atoms lead to an increase in magnetic anisotropy energy, a coupling of individual Co-rich clusters, and the concomitant blocking of their magnetic moments. The large obtained magnetic switching effects upon hydrogen-charging at room temperature (αC,V > 400 Oe V−1; ΔM = 1.5 emu g−1) open up new possibilities to use magneto-ionic effects for real-life applications in magnetic devices.

Nanoporous Pd–Cu–Si Amorphous Thin Films for Electrochemical Hydrogen Storage and Sensing

Increasing the efficiency of hydrogen storage and release using recent generation metallic glass nanofilms (MGNFs) offers green solutions for nanoscale energy applications. Contrary to flat nanofil...

The Promoting Effect of MxOy(M = Zr, Ti, Co, Ni) to 3D Nanoporous Pd for Ethanol Electrooxidation

In this work, a series of three dimensions nanoporous Pd/MxOy ([Formula: see text], Ti, Co, Ni) composites are directly prepared by a simple dealloying method, their electrocatalytic performances are investigated. The structure analysis results show that the pores size of the composites is distinctly reduced, and their specific surface area is obviously increased compared with the nanoporous Pd when adding MxOy. As an anode catalyst, these three-dimensional (3D) nanoporous Pd/MxOy composites exhibit remarkable electrocatalytic performance (activity and stability) than that of the nanoporous Pd for ethanol electrooxidation, the order of the performance is as follows: Pd/NiO [Formula: see text] Pd/Co2O3 s [Formula: see text] Pd/TiO2 s [Formula: see text] Pd/ZrO[Formula: see text] Pd. Among the composites, the nanoporous Pd/NiO composite shows the best performance, which is approximately 3.6 times that of the single nanoporous Pd. The performance improvement of the composites for the ethanol oxidation is attributed to the structure optimization, interfacial electronic effect and dual functional mechanism between Pd and MxOy.

The free-standing nanoporous palladium for hydrogen isotope storage

Herein, we present hydrogen isotope storage properties of the free-standing monolithic nanoporous palladium (NP–Pd) with different microstructure feature sizes. The NP-Pd samples fabricated by dealloying from Pd–Al alloy and the samples possess high surface area with all of the open pores and ligaments both at nanoscale, which provide the large quantities of reaction sites. The NP-Pd exhibits efficient hydrogen (H2) separation property from deuterium (D2) with distinguishable absorbing and desorbing plateau pressures. The samples own high and reversible H2 and D2 storage capacities with the absorption values up to 0.61 and 0.595 at room temperature. The hydrogen isotope storage capacities increase with the ligament sizes of the NP-Pd samples, which have been high temperature annealed with the larger ligament size more than 10 nm. While for the fresh dealloyed NP-Pd samples with rough surface and ligament size much smaller than 10 nm, the capacity does not follow this behavior. Therefore, a theoretical model based on the existence of the different storage sites at subsurface and interior region is established, which can be used to predict the hydrogen absorption capacity of nanoporous Pd with different structure size. This work reveals both fundamental insights and practical guidance for nanoporous materials design and fabrication, which can be applied in hydrogen isotope separation and storage applications in green energy fields.

Evolution of superparamagnetism in the electrochemical dealloying process

In situ superconducting quantum interference device magnetometry provides insights into the electrochemical dealloying mechanism of a CoPd alloy. Charge-dependent measurements of magnetic moment allow the separation of primary and secondary dealloying contributions. Coercivity evolution revealed the transition from collective ferromagnetism to superparamagnetism of small alloy clusters evolving in the dealloying process, which is interpreted as an “inverse” magnetic percolation problem. Temperature-dependent magnetization curves enable a qualitative comparison of magnetic cluster size distributions in the nanoporous Pd framework, which are found to be strongly influenced by dealloying potential. The study underlines the potential of electrochemical dealloying as a promising method for the preparation of tailor-made magnetic nanostructures.

Nanoporous metal-polymer composite membranes for organics separations and catalysis.

Metallic thin-film composite membranes are produced by sputtering metal films onto commercial polymer membranes. The separations capability of the membrane substrate is enhanced with the addition of a 10 nm Ta film. The addition of a tantalum layer decreases the molecular weight cutoff of the membrane from 70 kDa dextran (19 nm) to below 5 kDa (6 nm). Water flux drops from 168 LMH/bar (LMH: liters/meters2/hour) (polymer support) to 8.8 LMH/bar (Ta composite). A nanoporous layer is also added to the surface through Mg/Pd film deposition and dealloying. The resulting nanoporous Pd is a promising catalyst with a ligament size of 4.1 ± 0.9 nm. The composite membrane's ability to treat water contaminated with chlorinated organic compounds (COCs) is determined. When pressurized with hydrogen gas, the nanoporous Pd composite removes over 70% of PCB-1, a model COC, with one pass. These nanostructured films can be incorporated onto membrane supports enabling diverse reactions and separations.

Pore-Size-Tuned Pd Films Grown on Ni Foam as an Advanced Catalyst for Electrosynthesis of Ammonia

Electrochemical ammonia synthesis is considered as an alternative sustainable method to the traditional Haber–Bosch process because of the reduced energy consumption and mild operation conditions. The key is to design efficient electrocatalysts for facile adsorption and activation of nitrogen. Herein, a nanoporous Pd film with a tunable pore size has been in situ grown on Ni foam (nPd/NF) via a micelle-assisted replacement method using NF as a reductant and substrate, where polystyrene-b-poly­(ethylene oxide) and 1,3,5-triisopropylbenzene serve as a pore-forming agent and a swelling agent, respectively. Combining the continuous large nanoporous structure and self-supported properties, the obtained nPd/NF exhibits excellent catalytic performance for ammonia synthesis with a high NH3 yield of 18.27 μg h–1 mgcat–1 and a faradaic efficiency of 10.36% in 0.1 M Na2SO4. This work provides a fascinating route for the rational design of self-supported porous noble metals with a tunable pore size for effective electrosynthesis of ammonia.

Enhanced reversible hydrogen storage in palladium hollow spheres

Palladium has long been used as a hydrogen sponge because of its ability to store hydrogen under ambient conditions (room temperature and 1 bar pressure). However, Pd suffers from a low storage capacity. The current investigation pertains to the enhancement in the reversible hydrogen storage capacity of Pd, by using hollow sphere geometry. Additional storage is achieved in molecular form; thus utilizing a recently developed multi-mode storage strategy. Hollow spheres, which can be viewed as nanocontainers, have been synthesized using a chemical reduction method (outer diameter of ∼300 nm and shell thickness ∼20 nm). Pressure-composition-isotherms have been used to characterize the hydrogen storage capacity and to establish the reversibility of the process. A 54% enhancement in the reversible storage capacity (25 °C and 140 bar) is observed in the case of Pd hollow spheres as compared to that of bulk Pd and 70% with respect to that of nanoporous Pd. The outer and inner surfaces of the hollow sphere play contrasting catalytic roles in the absorption and desorption process.