Exploring efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is critical for developing anion exchange membrane electrolyzers. The key to a rational catalyst design is understanding the descriptors that govern the alkaline HER activity. Unfortunately, the principles that govern the alkaline HER performance remain unclear and are still under debate. By studying the alkaline HER at a series of NiCu bimetallic surfaces, where the electronic structure is modulated by the ligand effect, we demonstrate that alkaline HER activity can be correlated with either the calculated or the experimental-measured d band center (an indicator of hydrogen binding energy) via a volcano-type relationship. Such correlation indicates the descriptor role of the d band center, and this hypothesis is further supported by the evidence that combining Ni and Cu produces a variety of adsorption sites, which possess near-optimal hydrogen binding energy. Our finding broadens the applicability of d band theory to activity prediction of metal electrocatalysts and may offer an insightful understanding of alkaline HER mechanism.
Silica coated mesoporous Fe (Fe@SiO2) microcubes were designed for high performance electromagnetic wave attenuation. Silica coating lowered the permittivity significantly compared to that for bare Fe cubes. Most importantly, even with the silica coating the iron particles kept their shape which ensured a mesoporous structure. The synthetic approach consists of three steps. α-Fe2O3 microcubes were first synthesized by a hydrothermal method. Then, the cubes were coated with silica. The silica coated α-Fe2O3 microcubes were finally reduced under hydrogen gas at 500 °C. The reduction of iron oxide resulted in a removal of oxygen atoms and subsequently left the empty space as pores inside the silica coated iron cubes. The silicon resin composites containing Fe@SiO2 microcubes exhibited impressive electromagnetic wave attenuation characteristics. The reflection loss value of −54 dB could be obtained at 3.2 GHz with a thickness of 4.5 mm. In addition, the mesoporous characteristic offered a low density of Fe@SiO2 mesoporous microcubes. The microcubes enabled a reflection loss of −15 dB with a film thickness as thin as 3 mm. The silica coated mesoporous iron microcubes significantly reduced the usage/thickness of silicon resin composite. They are very promising as a strong attenuation and lightweight electromagnetic wave attenuation material.
Fuel cells represent an attractive technology for tomorrow's energy vector because hydrogen is an efficient fuel and environmentally clean, but one of the important challenges for fuel cell commercialization is the preparation of active, robust and low-cost catalysts. The synthesis and processing of molecularly-capped multimetallic nanoparticles, as described in this report, serves as an intriguing way to address this challenge. Such nanoparticles are exploited as building blocks for engineering the nanoscale catalytic materials by taking advantage of diverse attributes, including monodispersity, processability, solubility, stability, capability in terms of size, shape, composition and surface properties. This article discusses recent findings of our investigations of the synthesis and processing of nanostructured catalysts with controlled size, composition, and surface properties by highlighting a few examples of bimetallic/trimetallic nanoparticles and supported catalysts for electrocatalytic oxygen reduction.
Pure graphene exhibited a layered structure with a very smooth surface, while wrinkles were observed in the hybrid sample both at the edge of the graphene sheets and on the interlayer nanosheets. The tubular materials were distributed randomly on the surface of graphene nanosheets with the tubular axes being parallel to the graphene nanosheets. The electrodeposition process has been shown to be an effective technique to synthesize manganese oxide-based hybrids with graphene nanosheets. Nickel oxide–graphene hybrids are mainly based on NiO, with major applications in energy storage devices, i.e., supercapacitors and lithium ion batteries, and have been synthesized by using various methods. The graphene layer had a monolayer structure, with uniform contrast for visible hexagonal atomic lattice. Hybrids of graphene or graphene oxides with various complex oxides and multiple oxides have been reported.
Mechano-optical systems with on-demand adaptability and a broad spectrum from the visible to microwave are critical for complex multiband electromagnetic (EM) applications. Most existing material systems merely have dynamic optical or microwave tunability because their EM wave response is strongly wavelength-dependent. Inspired by cephalopod skin, we develop an adaptive multispectral mechano-optical system based on bilayer acrylic dielectric elastomer (ADE)/silver nanowire (AgNW) films, which reconfigures the surface morphology between wrinkles and cracks via mechanical contraction and stretching. Such morphological evolution regulates the direct transmission/reflection and scattering behavior of visible-infrared light and simultaneously alters the conductive network in a AgNW film to influence its microwave characteristics. The designed system features switching between visible-infrared-microwave transparency and opacity, continuous regulation, wide spectral window (0.38-15.5 μm and 24,200-36,600 μm), excellent recyclability (500 times), and rapid response time (<1 s). These grant the system great potential as platforms for various promising applications such as smart windows, switchable EM devices, dynamic thermal management, adaptive visual stealth, and human motion detection.
Abstract The hydrogen evolution reaction (HER) on a noble metal surface in alkaline media is more sluggish than that in acidic media due to the limited proton supply. To promote the reaction, it is necessary to transform the alkaline HER mechanism via a multisite catalyst, which has additional water dissociation sites to improve the proton supply to an optimal level. Here, this study reports a top‐down strategy to create a multisite HER catalyst on a nano‐Pd surface and how to further fine‐tune the areal ratio of the water dissociation component to the noble metal surface in core/shell‐structured nanoparticles (NPs). Starting with Pd/Fe 3 O 4 core/shell NPs, electrochemical cycling is used to tune the coverage of iron (oxy)hydroxide on a Pd surface. The alkaline HER activity of the core/sell Pd/FeO x (OH) 2−2 x NPs exhibits a volcano‐shaped correlation with the surface Fe species coverage. This indicates an optimum coverage level where the rates of both the water dissociation step and the hydrogen formation step are balanced to achieve the highest efficiency. This multisite strategy assigns multiple reaction steps to different catalytic sites, and should also be extendable to other core/shell NPs to optimize their HER activity in alkaline media.
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