The enhanced electrocatalytic activity and stability of NiW films electrodeposited under super gravity field for hydrogen evolution reaction

NiW films as cathode materials for hydrogen evolution reaction (HER) were electrodeposited under various gravity conditions. The morphologies of NiW films were characterized by SEM. Tafel curves and electrochemical impedance spectroscopy (EIS) were determined to study the electrocatalytic activity and stability of NiW films for HER in 10% NaOH solution. The results indicated that NiW films electrodeposited under normal gravity condition consisted of cellular grains and microcracks. Both surface morphologies and electrocatalytic activities of NiW films were not improved obviously by adjusting solution composition and current density. However, NiW films with fine grains and fewer microcracks were electrodeposited under super gravity field. The electrocatalytic activities of NiW films for HER increased with gravity coefficient (G) value. Meanwhile, NiW films showed excellent stability. During shut-down electrolysis, corrosion resistances of NiW film electrodeposited under G value of 256 were always higher than those of NiW film electrodeposited under normal gravity condition.     

Nanoporous Ag–ZrO2 composites prepared by chemical dealloying for borohydride electro-oxidation

A novel two-step dealloying method is adopted to prepare nanoporous Ag–ZrO₂ composite catalysts with the enhanced electrocatalytic performance by chemical dealloying of the melt-spun Al–Ag–Zr precursory alloys. The Zr atoms released from the precursory alloys are oxidized into ZrO₂ during dealloying and are loaded on the inner surface of nanoporous Ag. The dealloyed ribbons exhibit an interpenetrating ligament-channel structure with nanometer length scales. The X-ray Photoelectron Spectroscopy (XPS) results reveal that the electron charge transfer takes place between ZrO₂ film and Ag ligaments. The electrochemical tests demonstrate that the current density peak increases with calcination temperatures in a certain range and that the nanoporous composites with optimized ZrO₂ content exhibit a higher catalytic activity, resulting in the oxidation current density increase of 91.3% compared with nanoporous Ag. The excellent catalytic activity can be attributed to the interfacial interaction and electron charge transfer between Ag and ZrO₂.     

Electrochemical performances of nanostructured Ni3P–Ni films electrodeposited on nickel foam substrate

Ni₃P–Ni films were deposited on nickel foam substrates by electrodeposition in an aqueous solution. The structure and morphology of the electrodeposited films were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM). The annealed electrodeposited films consisted of tetragonal structured Ni₃P and cubic metal Ni. As anode for lithium ion batteries, the electrochemical properties of the Ni₃P–Ni films were investigated by cyclic voltammetry (CV), electrochemical impedance spectrum (EIS) and galvanostatic charge–discharge tests. The electrodeposition time had a significant effect on the electrochemical performances of the films. The Ni₃P–Ni film electrodeposited for 20 min delivered the initial discharge capacity of 890 mAh g⁻¹. Although the irreversible capacity at the first cycle was relative large, the Ni₃P–Ni film exhibited good cycling stability and its discharging capacity still maintained 340 mAh g⁻¹ after 40 cycles.     

Electrochemical deposition of porous Co3O4 nanostructured thin film for lithium-ion battery

Porous Co₃O₄ nanostructured thin films are electrodeposited by controlling the concentration of Co(NO₃)₂ aqueous solution on nickel sheets, and then sintered at 300 °C for 3 h. The as-prepared thin films are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The electrochemical measurements show that the highly porous Co₃O₄ thin film with the highest electrochemically active specific surface area (68.64 m² g⁻¹) yields the best electrochemical performance compared with another, less-porous film and with a non-porous film. The highest specific capacity (513 mAh g⁻¹ after 50 cycles) is obtained from the thinnest film with Co₃O₄ loaded at rate of 0.05 mg cm⁻². The present research demonstrates that electrode morphology is one of the crucial factors that affect the electrochemical properties of electrodes.     

Ni-W nanostructure well-marked by Ni selective etching for enhanced hydrogen evolution reaction

Designing active, stable and affordable electrocatalysts is a promising pathway for fulfilling the mankind's dream of preserving unsustainable fuel sources. Herein, the facile utilization of Romanesco-like and arrow-like nanostructures of Ni-W samples is introduced. Exclusive emphasis is placed on achievement of the unique nanostructure through cost-effective, repeatable and readily accessible two-step techniques, i.e. Ni-W electrodeposition approach followed by etching treatment. Microscopic study was fully utilized for surface morphology and structural investigation. The electrochemical analysis was used to evaluate the electrocatalytic activity and stability. The surface roughness of the Ni-W film electrodeposited by D.C = 90% and etched via acidic solution was up to 93.85, considerably higher than that of the Ni-W electrodeposited by D.C = 20% and without etched Ni-W films (55.36 and 41.51 respectively). Therefore, HER activity was improved with η₁₀ and η₂₀ of 169 and 226 mV vs. RHE, respectively, due to higher effective active surface for H⁺ adsorption. The Tafel slope analysis suggests Volmer mechanism as the HER rate-determining step. The electrochemically active surface area was also enhanced from roughly 2 to 10 cm². In addition, wettability was investigated by a contact angle of less than 65°, which indicates high penetration of electrolyte to the nanostructure. Rapid separation of bubbles on the arrow-like nanostructure of Ni-W films exhibited unstable H₂ bubbles on surface of the electrode.     

Combinatorial development of nanoporous WO3 thin film photoelectrodes for solar water splitting by dealloying of binary alloys

A combinatorial materials approach is suggested for the development of nanoporous thin film oxides for photoelectrochemical solar water splitting. As a precursor for nanoporous WO₃ films, metallic nanoporous W films were synthesized by dealloying sputtered W_1−xAl_x and W_1−xFe_x (0.06 < x < 0.67) thin film materials libraries in aqueous HNO₃ solutions with different concentrations for 24 h under open circuit conditions. The variation of the etchant concentration provided different film nanostructures. The films were then transformed into nanoporous WO₃ by controlled thermal oxidation at 500 °C in air. Screening of the photoelectrochemical properties of nanoporous WO₃ films shows a strong porosity- and thickness-dependence of the photocurrent. At the same time the photocurrent density does not depend on precursor composition, because dealloying in acid solutions of certain concentration leads to formation of identical nanostructures in a broad range of precursor compositions.     

Electrochemical catalytic activities of nanoporous palladium rods for methanol electro-oxidation

A novel electrocatalyst, nanoporous palladium (npPd) rods can be facilely fabricated by dealloying a binary Al₈₀Pd₂₀ alloy in a 5 wt.% HCl aqueous solution under free corrosion conditions. The microstructure of these nanoporous palladium rods has been characterized using scanning electron microscopy and transmission electron microscopy. The results show that each Pd rod is several microns in length and several hundred nanometers in diameter. Moreover, all the rods exhibit a typical three-dimensional bicontinuous interpenetrating ligament-channel structure with length scale of 15-20 nm. The electrochemical experiments demonstrate that these peculiar nanoporous palladium rods (mixed with Vulcan XC-72 carbon powders to form a npPd/C catalyst) reveal a superior electrocatalytic performance toward methanol oxidation in the alkaline media. In addition, the electrocatalytic activity obviously depends on the metal loading on the electrode and will reach to the highest level (223.52 mA mg⁻¹) when applying 0.4 mg cm⁻² metal loading on the electrode. Moreover, a competing adsorption mechanism should exist when performing methanol oxidation on the surface of npPd rods, and the electro-oxidation reaction is a diffusion-controlled electrochemical process. Due to the advantages of simplicity and high efficiency in the mass production, the npPd rods can act as a promising candidate for the anode catalyst for direct methanol fuel cells (DMFCs).     

Preparation of FeNi-based nanoporous amorphous alloy films and their electrocatalytic oxygen evolution properties

The progress of this research is the preparation of FeNi alloy thin films by magnetron sputtering. Each step of the experimental process is based on the electrocatalytic performance of the sample, and characterized by many characterizations means such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray energy spectrometry (EDS) and step gauge thickness test for morphology, structure and elemental composition, etc. The analysis of the characterization results is used as a support for the experimental process. Adjustment of various preparation process parameters for material growth and subsequent processing include doping of non-metallic elements and construction of nanostructures. Doping of C elements can make FeNi based alloy films further amorphous. Zn element is used as a pore-forming agent. The two processes of doping and high-temperature vacuum dealloying can make the film obtain a nanoporous structure, which greatly increases the specific surface area. These two strategies reduce the overpotential (η10) of oxygen evolution reaction (OER) of FeNi alloy thin films to 393 mV and 314 mV, which are reduced by 47 mV and 79 mV step by step. The electrochemical properties of the finally obtained alloy film are: overpotential of 314 mV, Tafel slope of 61.8 mV/dec and the stability of only 10% decay at a current density of 10 mA/cm2 for 12 h. In this study, low-cost transition metals were used as the main materials to design OER catalysts, and the catalytic efficiency was comparable to that of commercial noble metal catalysts. The physical preparation methods made each sample have good reproducibility. It provides the experimental basis and theoretical basis for the design and synthesis of new catalytic materials at a higher level.     

3D nanostructured nickel film supported to a conducting polymer as an electrocatalyst with exceptional properties for hydrogen evolution reaction

A two-layer system was applied to a nickel substrate for use as the electrocatalyst of the hydrogen evolution reaction (HER) in a phosphate buffer solution. It was comprised of a three-dimensional (3D) porous underlayer of nickel nanoparticles with a size of less than 35 nm, followed by an electrodeposited top layer of poly (aniline-co-pyrrole). The underlayer and top coating were both synthesized by applying a constant potential to a three-electrode system. The catalyst characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectrometry. The electrocatalytic activity of the fabricated electrodes was measured by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The electrode exhibited an overpotential of 520 mV at a current density of 10 mA cm⁻², comparable to 530 mV of platinum. Furthermore, the Tafel slope of the electrode was 90 mV dec⁻¹, almost equal to that of platinum. This exceptional performance was explained by the synergistic interaction between 3D-Ni and poly (aniline-co-pyrrole) layers. Such a synergism was demonstrated by the fact that the resulting electrode lacked substantial catalytic activity when each of these two layers was deposited on the substrate alone. The Nyquist diagrams revealed that the 3D-Ni film resulted in minimal charge transfer resistance, allowing fast kinetics of HER. The coupling of this property with the ability of the polymer to adsorb H⁺ ions led to the high electrocatalytic activity of the proposed electrode. This electrode performed better than platinum, which was a promising result. This indicated that a lower voltage input was required to generate hydrogen gas using the prepared electrode.     

Electrochemical performance of porous Ni3Al electrodes for hydrogen evolution reaction

Porous Ni₃Al intermetallic material with a mean pore diameter of around 1 μm was prepared by step sintering Ni and Al powder pressed compacts in vacuum furnace at 900 °C. The electrocatalytic activity of the as-fabricated porous Ni₃Al material as an electrode for hydrogen evolution reaction (HER) in alkaline solutions was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. It is found that the onset potential of porous Ni₃Al for HER shifted in the positive direction favoring hydrogen generation with lower overpotential, compared with foam Ni and dense Ni electrodes. Effects of electrolyte concentration and temperature on HER as well as the electrochemical stability in alkaline solution were investigated and the electrochemical activation energy was determined for the porous Ni₃Al. The increased activity for HER was attributed to the high porosity, an increased electrochemical surface area and the nanostructure of porous Ni₃Al electrode. The corrosion tests showed that the corrosion resistance of porous Ni₃Al electrode changed during the immersion process due to the formation of passive film layers.     

Self-supported hierarchical porous FeNiCo-based amorphous alloys as high-efficiency bifunctional electrocatalysts toward overall water splitting

Rationally designing an efficient and cost-effective bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a primary matter in applying electrocatalytic water splitting. Herein, a self-supported FeNiCo-based amorphous catalyst with a hierarchical micro/nanoporous structure is fabricated by dealloying an amorphous/nanocrystalline precursor. The amorphous nanoporous framework enables the prepared electrocatalyst to afford fast reaction kinetics, abundant active sites, and enhanced electrochemical active surface areas (ECSAs). Such structural advantages and the synergistic effects of the ternary transition metals contribute to a dramatic catalytic activity of this electrocatalyst under alkaline conditions, which delivers the current density of 10 mA cm⁻² at a low overpotential of 134 mV for HER and 206 mV for OER, respectively. Furthermore, a full electrolysis apparatus constructed by the self-supported hierarchical micro/nanoporous FeNiCo-based amorphous electrocatalyst as both cathode and anode acquires a dramatically low voltage of 1.58 V operating at 10 mA cm⁻² along with stability for more than 24 h for overall water splitting.     

Enhanced rate capability of multi-layered ordered porous nickel phosphide film as anode for lithium ion batteries

Porous nickel phosphide films are fabricated by electrodeposition through self-assembled polystyrene sphere multi-layers as template. After the removal of the template, well-ordered and close-packed spherical pores are left in the films. The thin walls of the adjacent pores make up a three-dimensional network nanostructure in the triple-layer porous Ni₃P film. The as-prepared triple-layer porous film delivers significantly enhanced rate capability over the single- and double-layer ones. After 50 cycles, the capacity of the triple-layer Ni₃P porous film still sustains 557 mAh g⁻¹ and 243 mAh g⁻¹ at a charge-discharge rate of 0.2 C and 5 C (1 C = 388 mA g⁻¹), respectively. According to the analysis of electrochemical impedance spectrum (EIS), the improved electrochemical performance of the triple-layer film can be attributed to the fast migration of Li⁺ through surface-passivating layer and the facilitated charge transfer into Ni₃P three-dimensional network nanostructure.     

Facile fabrication and electrocatalytic activity of Pt0.9Pd0.1 alloy film catalysts

A nano-thickness porous Pt_0.9Pd_0.1 alloy film with a greatly enhanced surface area were firstly synthesized at a glassy carbon electrode (GCE) using a facile cyclic voltammetry (CV) method. The atomic ratio of the alloy can be controlled by controlling the composition of the electrodeposition solution. We found that small amount of alloying Pd is an excellent catalytically enhancing agent for the Pt catalyst, and 10% Pd is the optimal. The structures of the Pt_0.9Pd_0.1 alloy film were characterized by FE-SEM, XPS, XRD and electrochemical techniques. It was found that the Pt_0.9Pd_0.1 film was in nanoporous structure and consisted of crystallites of 10.1 nm on average, leading to the modified electrode (Pt_0.9Pd_0.1/GCE) has an effective surface area as large as 790 times that of a corresponding bare Pt disk electrode. The Pt_0.9Pd_0.1/GCE exhibited significantly higher stability and catalytic activity for both of the methanol electro-oxidation reaction (MOR) and the oxygen electro-reduction reaction (ORR) than the correspondingly electrodeposited Pt modified GCE. The advantage can be attributed to the CV-prepared nano-porous structure on the electrode surface. This method and the prepared electrode can be expected to have promising applications in biosensors and fuel cells, etc.     

Nickel foam supported Sn-Co alloy film as anode for lithium ion batteries

Sn-Co alloy films are deposited electrochemically directly onto nickel foam in an aqueous solution. The influence of electrochemical current density and heat treatment on the structure and morphology of the electrodeposited films is studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the Sn-Co alloy films are further investigated by galvanostatic charge-discharge tests. As anodes for lithium ion batteries, the Sn-Co alloy-film anodes, after further heat treatment at 200 °C for 30 min, delivers a specific capacity of 663 mAh g⁻¹ after 60 cycles. This high capacity retention is attributed to the unique electrode configuration with an enhanced interface strength between the active material and the current collector formed in the heat-treatment process.     

Controlled galvanic decoration boosting catalysis: Enhanced glycerol electro-oxidation at Cu/Ni modified macroporous films

We report on glycerol electro-oxidation in alkaline medium at macroporous Ni electrodes decorated with Cu particles. Macroporous Ni film is electrodeposited, using hydrogen bubbles as dynamic templates, atop of a Cu substrate. This film shows good electrocatalytic activity towards glycerol oxidation reaction (GOR). The Ni film is further decorated with Cu via spontaneous deposition from CuSO₄ solution. This is done to enhance the catalytic activity of the film towards GOR. The morphology of the Cu-decorated Ni film is controlled using various additives such as KCl and (NH₄)₂SO₄ which are added to the Cu deposition bath. The as-prepared Cu-decorated Ni films are characterized by electrochemical measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that these additives have tremendous effects on the morphology and the electrocatalytic activity of the decorating Cu particles.The decorated Ni foam showed superior electrocatalytic activity towards the GOR, as confirmed by the negative shift in the onset oxidation potential (ca. 100 mV) together with an increase in oxidation current that is up to 1.5-fold during the cyclic voltammetry (CV) measurements, compared to the undecorated Ni foam.     

Double-template fabrication of three-dimensional porous nickel electrodes for hydrogen evolution reaction

Three-dimensional (3D) porous nickel structures were fabricated via a double-template electrochemical deposition process. The construction of the foam structures was achieved by means of a hydrogen bubble dynamic template, prepared from Cu electrodeposition at high current densities. Subsequently, a Ni layer was electrodeposited on the Cu 3D template. During the nickel coating, the typical finger-like microstructure of the Cu foam becomes denser and changes to a cauliflower microstructure. The hydrogen evolution reaction (HER) on these macroporous Ni electrodes was evaluated in 30 wt.% KOH solution by means of polarization curves and electrochemical impedance spectroscopy (EIS). Results demonstrate greater apparent activity of the developed electrodes towards HER in comparison with commercial smooth Ni electrode. The 3D porous Ni electrocatalyst obtained from Cu templates synthesized at the lowest current density and the highest electrodeposition time yielded the best electrochemical activity for HER.     

Rapid fabrication of Cu/Pd nano/micro-particles porous-structured catalyst using hydrogen bubbles dynamic template and their enhanced catalytic performance for formic acid electrooxidation

In this work, a self-supporting Pd–Cu bimetallic film with 3D porous structure was electrodeposited at the surface of glassy carbon electrode (GCE) using a facile double-template fabrication process, including hydrogen bubble templating method and galvanic replacement reaction, and its performance investigated as a catalyst for formic acid oxidation (FAO). The structure of the Cu/Pd porous film was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrocatalytic activity of the as-prepared catalysts with high surface areas were evaluated in sulfuric acid solution containing 1 M formic acid using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Cu/Pd porous structure exhibited significantly high current densities of formic acid oxidation compared to the Cu/Pd particles film catalyst. The effects of galvanic replacement time and concentration of formic acid on the catalytic activity of as-prepared electrode for FAO were comparatively investigated.     

Nanoporous bismuth electrocatalyst with high performance for glucose oxidation application

Although direct glucose fuel cell (DGFC) is widely regarded as one of the most promising energy systems, the low catalytic activity and inferior instability of most anode catalysts during electro-oxidation of glucose has greatly hampered its potential applications. In this work, an efficient and durable anode catalyst of nanoporous bismuth (Bi) for the alkaline electro-oxidation of glucose was proposed just by a simple de-alloying method. The microstructure and catalytic performance of nanoporous bismuth could be finely tuning through actively controlling the composition of precursor Mg–Bi alloy. A three-dimension structure was formed after de-alloying Mg–Bi precursor, giving rise to an increased specific surface area and correspondingly resulting in an enhanced electro-catalytic performance. It has intimated that the optimal nanoporous Bi catalyst with an open, bi-continuous interpenetrating pore-to-ligament structure was constructed based on Mg₆₅Bi₃₅ alloy etching and exhibited an enhanced current density (as high as 8.04 mA/cm²) during alkaline electro-oxidation of glucose, together with the lowest poisoning rate of 5.6 × 10^?3%. The remarkable electrochemical performance of the nanoporous Bi catalyst, coupling with facile dealloying strategy may facilitate design and development of renewable energy device.     

Influence of SiW12O404− on the electrocatalytic behaviour of Pt–Co alloy supported on carbon for water electrolysis in 3 M KOH aqueous solution

Pt–Co alloy supported on carbon (Pt–Co) was electroactivated with or without SiW₁₂O₄₀⁴⁻ and used as cathodes for the hydrogen evolution reaction (HER) in 3 M KOH at 70°C. These electrodes were characterised through neutron activation (NA) and electrochemical impedance spectroscopy (EIS). The best HER performances were observed on Pt–Co electroactivated with STA. The enhanced HER electrocatalytic activity observed on Pt–Co electroactivated with STA was attributed to an increase in its active surface area and to its surface chemical composition.     

Electrochemically assisted synthesis of three-dimensional FeP nanosheets to achieve high electrocatalytic activity for hydrogen evolution reaction

Iron phosphide (FeP) is a promising alternative catalyst for electrocatalytic hydrogen evolution reaction (HER) due to its low price, highly active catalytic sites and long-term anti-acid corrosion. Herein, we report a very facile strategy to fabricate novel FeP nanosheets as a HER electrocatalyst. Three-dimensional interconnected nanosheet structures of Fe₂O₃ (3D Fe₂O₃ NS) were directly exfoliated from metal Fe wires by alternating current (AC) voltage disturbance, and a simple subsequent phosphorization process could easily convert γ-Fe₂O₃ into FeP phase, which also maintained the 3D NS structure. Importantly, increasing the AC voltage resulted in the evolution of iron-containing nanostructures from nanoparticles to 2D nanosheets until the formation of 3D NS structure. Owing to the large specific surface area, enriched active sites and abundant hierarchical porous channels, as-prepared 3D FeP NS has exhibited significantly enhanced electrocatalytic HER activities such as a cathode current density of 10 mA cm⁻² at a small overpotential of 88 mV, low Tafel slope (47.7 mV dec⁻¹) and satisfactory long-term stability in acidic electrolyte. We expect that this simple and green synthetic strategy of transition metal phosphides will provide a promising prospect to innovate nonprecious HER electrocatalysts.