Eric Detsi

Enhanced Strain in Functional Nanoporous Gold with a Dual Microscopic Length Scale Structure

We have synthesized nanoporous Au with a dual microscopic length scale by exploiting the crystal structure of the alloy precursor. The synthesized mesoscopic material is characterized by stacked Au layers of submicrometer thickness. In addition, each layer displays nanoporosity through the entire bulk. It is shown that the thickness of these layers can be tailored via the grain size of the alloy precursor. The two-length-scale structure enhances the functional properties of nanoporous gold, leading to charge-induced strains of amplitude up to 6%, which are roughly 2 orders of magnitude larger than in nanoporous Au with the standard one-length-scale porous morphology. A model is presented to describe these phenomena.

Metallic Muscles at Work: High Rate Actuation in Nanoporous Gold/Polyaniline Composites

Metallic muscles made of nanoporous metals suffer from serious drawbacks caused by the usage of an aqueous electrolyte for actuation. An aqueous electrolyte prohibits metallic muscles from operating in dry environments and hampers a high actuation rate due to the low ionic conductivity of electrolytes. In addition, redox reactions involved in electrochemical actuation severely coarsen the ligaments of nanoporous metals, leading to a substantial loss in performance of the actuator. Here we present an electrolyte-free approach to put metallic muscles to work via a metal/polymer interface. A nanocoating of polyaniline doped with sulfuric acid was grown onto the ligaments of nanoporous gold. Dopant sulfate anions coadsorbed into the polymer coating matrix were exploited to tune the nanoporous metal surface stress and subsequently generate macroscopic dimensional changes in the metal. Strain rates achieved in the single-component nanoporous metal/polymer composite actuator are 3 orders of magnitude higher than that of the standard three-component nanoporous metal/electrolyte hybrid actuator.

Mesoporous Ni60Fe30Mn10-alloy based metal/metal oxide composite thick films as highly active and robust oxygen evolution catalysts

A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ~350 mV overpotential to oxidize water with a current density of 10 mA/cm2 in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA/cm2 at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (~10 nm) results in a high BET surface area (43 m2/g) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ~3×104 cm2 of catalytic area per cm2 of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.

Reversible strain by physisorption in nanoporous gold

Reversible strain amplitudes up to 0.02% in response to a 15% change in relative humidity were detected in nanoporous gold. We show that the mechanism involved in dimensional changes during physisorption is associated with changes in the surface stress when molecules are adsorbed from the vapor phase onto the metal interface.

Nanoporous gold formation by dealloying: A Metropolis Monte Carlo study

a b s t r a c t A Metropolis Monte Carlo study of the dealloying mechanism leading to the formation of nanoporous gold is presented. A simple lattice-gas model for gold, silver and acid particles, vacancies and products of chemical reactions is adopted. The influence of temperature, concentration and lattice defects on the dealloying process is investigated and the morphological properties are characterized in terms of the Euler characteristic, volume, surface area and the specific surface area. It is shown that a minimal threeparameter model suffices to yield nanoporous gold structures which have morphological properties akin to those found in the experiment. The salient features of the structures found by simulation are that the ligament size of the dealloyed material is of the order of 2–3 nm, the structure is disordered, percolating and entirely connected.

Electrochromic artificial muscles based on nanoporous metal-polymer composites

This work shows that a nano-coating of electrochromic polymer grown onto the ligaments of nanoporous gold causes reversible dimensional and color changes during electrochemical actuation. This combination of electromechanical and optical properties opens additional avenues for the applications of artificial muscles, i.e., a metallic muscle exhibits its progress during work by changing color that can be detected by optical means.

Direct synthesis of metal nanoparticles with tunable porosity

Herein, we report a facile one-step synthesis route of porous bimetallic Au–Ag nanoparticles involving two parallel processes: alloying during nanocrystal growth and dealloying via galvanic replacement reaction. Further, we show that porosity in these nanoparticles can be tuned via their alloy composition. The specific surface area of the synthesized porous nanoparticles is significantly enhanced compared to that of their solid bulk counterparts.

On the localized surface plasmon resonance modes in nanoporous gold films

This work concentrates on the relation between plasmonic modes and the microstructure of nanoporous gold films. Based on experiments and computational analyses, we conclude that ligament as well as pore sizes need to be taken into account for an adequate physical description of the optical performance of a disordered nanoporous metal film as a function of its detailed microstructure.

Nanoporous Tin with a Granular Hierarchical Ligament Morphology as a Highly Stable Li-Ion Battery Anode

Next generation Li-ion batteries will require negative electrode materials with energy densities many-fold higher than that found in the graphitic carbon currently used in commercial Li-ion batteries. While various nanostructured alloying-type anode materials may satisfy that requirement, such materials do not always exhibit long cycle lifetimes and/or their processing routes are not always suitable for large-scale synthesis. Here, we report on a high-performance anode material for next generation Li-ion batteries made of nanoporous Sn powders with hierarchical ligament morphology. This material system combines both long cycle lifetimes (more than 72% capacity retention after 350 cycles), high capacity (693 mAh/g, nearly twice that of commercial graphitic carbon), good charging/discharging capabilities (545 mAh/g at 1 A/g, 1.5C), and a scalable processing route that involves selective alloy corrosion. The good cycling performance of this system is attributed to its nanoporous architecture and its unique hierarchical ligament morphology, which accommodates the large volume changes taking place during lithiation, as confirmed by synchrotron-based ex-situ X-ray 3D tomography analysis. Our findings are an important step for the development of high-performance Li-ion batteries.

Deformation of nanoporous nanopillars by ion beam-induced bending

We have applied a novel approach to the investigation of deformation of nanoporous metals at the nanoscale by exposing nanoporous nanopillars to a Ga+ ion beam. We will show the results that we have obtained with Au nanopillars, but we have also observed similar behaviors in Cu, Al, and Ni nanopillars, i.e., a gradual massive deformation effect of the pillar during Ga ion beam exposure, where the pillar bends toward the ion beam. We derive a relationship between the formation of defects due to ion collisions in the nanopillars and the pillar’s deformations and find that the deflection is linearly related to ion fluence. Computational models have shown that the deflection rate can be varied through change in acceleration voltage. This occurs due to the dual influence of a decreasing bending arm which reduces the associated bending moment, as well as the decreasing ion concentration, and thus defect concentration at the peak stress point. The high degree of control over deflection and the variables that influence it open an opportunity for use of ion-induced bending as a characterization technique of mechanical performance.