Electrochemically Dealloying Engineering toward Integrated Monolithic Electrodes with Superior Electrochemical Li-Storage Properties

Integrated monolithic electrodes (IMEs) free of inactive components demonstrate great potential in boosting energy-power densities and cycling life of lithium-ion batteries. However, their practical applications are significantly limited by low active substance loading (< 4.0 mg cm-2 and 1.0 g cm-3), complicated manufacturing process, and high fabrication cost. Herein, employing industrial Cu-Mn alloy foil as a precursor, a simple neutral salt solution-mediated electrochemical dealloying strategy is proposed to address such problems. The resultant Cu-Mn IMEs achieve not only a significantly larger active material loading due to the in situ generated Cu2O and MnOx (ca. 16.0 mg cm-2 and 1.78 g cm-3), simultaneously fast transport of ions and electrons due to the well-formed nanoporous structure and built-in Cu current collector, but also high structural stability due to the interconnected ligaments and suitable free space to relieve the volume expansion upon lithiation. As a result, they demonstrate remarkable performances including large specific capacities (> 5.7 mAh cm-2), remarkable pseudocapacitive effect despite the battery-type constitutes, long cycling life, and good working condition in a lithium-ion full cell. This study sheds new light on the further development of IMEs, enriches the existing dealloying techniques, and builds a bridge between the two.

Nanoporous gold with microporous structure prepared by sodium dodecyl sulfate-mediated electrochemical dealloying

Nanoporous gold (NPG) is a promising catalytic material for the oxidation of CO and methanol applications. However, NPGs are prone to extensive macroscopic cracking that often decrease mechanic properties of NPGs and depresses their catalytic action. To produce crack-free NPG with an ultra-finer porosity in room temperature, the anionic surfactant sodium dodecyl sulfate (SDS) was added in electrochemical dealloying process. SDS has the effect of reducing the surface diffusion of gold which hinder the initial coarsening of ligaments and prevents interior silver atoms from being exposed and dissolved. As a result, the pore and ligment size are finer, but higher residual silver of NPG samples. NPG with pore size down to 2 nm and the ligament 4.0 nm was successfully fabricated with 13.32 mM SDS in perchloric acid solution. The surface diffusion coefficient of Au atoms was 1.6 × 10-24m2·s-1, nearly 3 orders of magnitude smaller than that of Au atoms in the absence of SDS (2.8 × 10-21m2·s-1). Nanoindentation results demonstrated that high residual silver content made NPG samples harder and stiffer，the specific surface areas of NPG with 6.66 mM SDS was 190 m2g-1by BET. This work provided very important clues on how to control the crack free ultrafine nanoporous structure of other materials.

The Tunable and Efficient Nanoporous CuAg Alloy Catalysts Toward Methanol Oxidation Reaction Synthesized by Electrochemical Dealloying of Metallic Glassy Precursors

Three-dimensional (3D) nanoporous CuAg (NPCuAg) alloy catalysts with various Cu/Ag ratios are prepared by electrochemical dealloying of metallic glassy (MG) precursors. All dealloyed samples exhibit homogenous nanoporous structure and element composition distribution. After systematically evaluating their electrocatalytic performance toward MOR, it was found that the catalytic activity of the NPCuAg catalysts is enhanced along with the increase of Cu/Ag ratio, which may be attributed to the more exposed active reaction sites derived from high surface area of nanoporous structure and the optimal synergistic effect. Thus, the NPCu_1.75 Ag alloy catalyst presents the best methanol electro-oxidation properties, including a high current density of 397.2 mA cm^-2 and good operation stability that retaining 84.5 % catalytic activity even after 7200 s. These results outperform most reported copper-based MOR catalysts in alkaline methanol solution. Considering these advantages, the designed electrodes are expected to be promising catalysts for alkaline DMFCs applications.

Surface Defects Improved SERS Activity of Nanoporous Gold Prepared by Electrochemical Dealloying

Nanoporous metals possess excellent catalytic and optical properties that are related with surface morphology. Here, we modulated the ligament surface of nanoporous gold (NPG) by controlling electrochemical dealloying and obtained NPG with an improved enhancement of its surface-enhanced Raman scattering (SERS) property. We found that both high-density atomic steps and kinks on the curved surfaces and high-content silver atoms close to the ligament surface contributed to the high SERS ability. The presented strategy will be useful for the fabrication of nanoporous metal with an excellent surface that is needed for sensing, conversion, and catalytic.

Electrochemical Performance and Hydrogen Storage of Ni-Pd-P-B Glassy Alloy

The search for hydrogen storage materials is a challenging task. In this work, we tried to test metallic glass-based pseudocapacitive material for electrochemical hydrogen storage potential. An alloy ingot with an atomic composition of Ni₆₀Pd₂₀P₁₆B₄ was prepared via arc melting of extremely pure elements in an Ar environment. A ribbon sample with a width of 2 mm and a thickness of 20 mm was produced via melt spinning of the prepared ingot. Electrochemical dealloying of the ribbon sample was conducted in 1 M H₂SO₄ to prepare a nanoporous glassy alloy. The Brunauer-Emmett-Teller (BET) and Langmuir methods were implemented to obtain the total surface area of the nanoporous glassy alloy ribbon. The obtained values were 6.486 m²/g and 15.082 m²/g, respectively. The Dubinin-Astakhov (DA) method was used to calculate pore radius and pore volume; those values were 1.07 nm and 0.09 cm³/g, respectively. Cyclic voltammetry of the dealloyed samples revealed the pseudocapacitive nature of this alloy. Impedance of the dealloying sample was measured at different frequencies through use of electrochemical impedance spectroscopy (EIS). A Cole-Cole plot established a semicircle with a radius of ~6 Ω at higher frequency, indicating low interfacial charge-transfer resistance, and an almost vertical Warburg slope at lower frequency, indicating fast diffusion of ions to the electrode surface. Charge-discharge experiments were performed at different constant currents (75, 100, 125, 150, and 200 mA/g) under a cutoff potential of 2.25 V vs. Ag/AgCl electrode in a 1 M KOH solution. The calculated maximum storage capacity was 950 mAh/g. High-rate dischargeability (HRD) and capacity retention (Sn) for the dealloyed glassy alloy ribbon sample were evaluated. The calculated capacity retention rate at the 40th cycle was 97%, which reveals high stability.

A novel dealloying strategy for fabricating nanoporous Ag via ζ'-AgGa alloy

A mild strategy for fabricating nanoporous silver (np-Ag) pieces was reported via preparation of Ag-Ga alloys in relatively low temperature and subsequent electrochemical dealloying in nitric acid (HNO₃) aqueous solution. After selectively etching Ga out of the Ag-Ga alloy, a typical three-dimensional (3D) bicontinuous nanoporous structure with a pore size of ∼67.21-159.33 nm was observed. A series of studies have shown that the addition of sodium dodecyl sulfate (SDS) results in minimum pore size. The coarsen exponent (n) is 1.61, and the activation energy was calculated to be 27.04 kJ mol^-1. Theζ'-AgGa alloy prepared at low temperature can be used as the precursor for the preparation of fine np-Ags, and this method provides a new strategy for the industrial production of dealloyed np-Ag.

Spontaneously Sn-Doped Bi/BiOx Core-Shell Nanowires Toward High-Performance CO2 Electroreduction to Liquid Fuel

Electrochemical CO₂ reduction provides a promising strategy to product value-added fuels and chemical feedstocks. However, it remains a grand challenge to further reduce the overpotentials and increase current density for large-scale applications. Here, spontaneously Sn doped Bi/BiOx nanowires (denoted as Bi/Bi(Sn)O_x NWs) with a core-shell structure were synthesized by an electrochemical dealloying strategy. The Bi/Bi(Sn)O_x NWs exhibit impressive formate selectivity over 92% from -0.5 to -0.9 V versus reversible hydrogen electrode (RHE) and achieve a current density of 301.4 mA cm^-2 at -1.0 V vs RHE. In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiO_x species can promote the stabilization of the *OCHO intermediate on the Bi(Sn)O_x surface and suppress the competitive H₂/CO production. This work provides effective in situ construction of the metal/metal oxide hybrid composites with heteroatom doping and new insights in promoting electrochemical CO₂ conversion into formate for practical applications.

Magneto-Ionic Switching of Superparamagnetism

Electrochemical reactions represent a promising approach to control magnetization via electric fields. Favorable reaction kinetics have made nanoporous materials particularly interesting for magnetic tuning experiments. A fully reversible ON and OFF switching of magnetism in nanoporous Pd(Co) at room temperature is demonstrated, triggered by electrochemical hydrogen sorption. Comprehensive magnetic characterization in combination with high-resolution scanning transmission electron microscopy reveals the presence of Co-rich, nanometer-sized clusters in the nanoporous Pd matrix with distinct superparamagnetic behavior. The strong magneto-ionic effect arises from coupling of the magnetic clusters via a Ruderman-Kittel-Kasuya-Yoshida-type interaction in the Pd matrix which is strengthened upon hydrogen sorption. This approach offers a new pathway for the voltage control of magnetism, for application in spintronic or microelectromagnetic devices.

Electrochemical Dealloying-Assisted Surface-Engineered Pd-Based Bifunctional Electrocatalyst for Formic Acid Oxidation and Oxygen Reduction

Synthesis of non-Pt bifunctional electrocatalyst for the anodic oxidation of liquid fuel and cathodic reduction of oxygen is of great interest in the development of energy conversion devices. We demonstrate a facile room-temperature synthesis of surface-engineered trimetallic alloy nanoelectrocatalyst based on Co, Cu, and Pd by thermodynamically favorable transmetallation reaction and electrochemical dealloying. The quasi-spherical Co _xCu _yPd _z trimetallic catalysts were synthesized by the thermodynamically favorable reaction of K₂PdCl₄ with sheetlike Co _mCu _n bimetallic alloy nanostructure. The surface engineering of Co _xCu _yPd _z was achieved by electrochemical dealloying. The surface-engineered alloy electrocatalyst exhibits excellent bifunctional activity toward formic acid oxidation reaction (FAOR) and oxygen reduction reaction (ORR) at same pH. The elemental composition and lattice strain control the electrocatalytic performance. The elemental composition-dependent compressive strain weakens the adsorption of oxygen-containing species and favors the facile electron transfer for FAOR and ORR. The engineered alloy electrocatalyst of Co_0.02Cu_13.8Pd_86.18 composition is highly durable and delivers high mass-specific activity for ORR and FAOR. It delivers mass-specific activities of 1.50 and 0.202 A/mg_Pd for FAOR and ORR, respectively, in acidic pH. The overall performance is superior to that of as-synthesized Pd and dealloyed bimetallic Co_2.7Pd_97.3 and Cu_5.61Pd_94.39 nanoelectrocatalysts.

Nanoporous Gold-Based Biofuel Cells on Contact Lenses

A lactate/O₂ enzymatic biofuel cell (EBFC) was prepared as a potential power source for wearable microelectronic devices. Mechanically stable and flexible nanoporous gold (NPG) electrodes were prepared using an electrochemical dealloying method consisting of a pre-anodization process and a subsequent electrochemical cleaning step. Bioanodes were prepared by the electrodeposition of an Os polymer and Pediococcus sp. lactate oxidase onto the NPG electrode. The electrocatalytic response to lactate could be tuned by adjusting the deposition time. Bilirubin oxidase from Myrothecium verrucaria was covalently attached to a diazonium-modified NPG surface. A flexible EBFC was prepared by placing the electrodes between two commercially available contact lenses to avoid direct contact with the eye. When tested in air-equilibrated artificial tear solutions (3 mM lactate), a maximum power density of 1.7 ± 0.1 μW cm^-2 and an open-circuit voltage of 380 ± 28 mV were obtained, values slightly lower than those obtained in phosphate buffer solution (2.4 ± 0.2 μW cm^-2 and 455 ± 21 mV, respectively). The decrease was mainly attributed to interference from ascorbate. After 5.5 h of operation, the EBFC retained 20% of the initial power output.

Electrochemical Dealloying of PdCu3 Nanoparticles to Achieve Pt-like Activity for the Hydrogen Evolution Reaction

Manipulating the d-band center of the metal surface and hence optimizing the free energy of hydrogen adsorption (ΔG_H ) close to the optimal adsorption energy (ΔG_H =0) for hydrogen evolution reaction (HER), is an efficient strategy to enhance the activity for HER. Herein, we report a oleylamine-mediated (acting as the solvent, stabilizer, and reducing agent) strategy to synthesize intermetallic PdCu₃ nanoparticles (NPs) without using any external reducing agent. Upon electrochemical cycling, PdCu₃ transforms into Pd-rich PdCu (ΔG_H =0.05 eV), exhibiting remarkably enhanced activity (with a current density of 25 mA cm^-2 at ∼69 mV overpotential) as an alternative to Pt for HER. The first-principle calculation suggests that formation of low coordination number Pd active sites alters the d-band center and hence optimal adsorption of hydrogen, leading to enhanced activity. This finding may provide guidelines towards the design and development of Pt-free highly active and robust electrocatalysts.