Cathodic Corrosion of a Bulk Wire to Nonaggregated Functional Nanocrystals and Nanoalloys

Nanoscale zerovalent copper (nZVC) catalyzed environmental remediation of organic and inorganic contaminants: A review

Over the past decade, the nano zerovalent copper has emerged as an effective nano-catalyst for the environment remediation processes due to its ease of synthesis, low cost, controllable particle size and high reactivity despite its release during the remediation process and related concentration dependent toxicities. However, the improvised techniques involving the use of supports or immobilizer for the synthesis of Cu⁰ has significantly increased its stability and motivated the researchers to explore the applicability of Cu⁰ for the environment remediation processes, which is evident from access to numerous reports on nano zerovalent copper mediated remediation of contaminants. Initially, this review allows the understanding of the various resources used to synthesize zerovalent copper nanomaterial and the structure of Cu⁰ nanoparticles, followed by focus on the reaction mechanism and the species involved in the contaminant remediation process. The studies comprehensively presented the application of nano zerovalent copper for remediation of organic/inorganic contaminants in combination with various oxidizing and reducing agents under oxic and anoxic conditions. Further, it was evaluated that the immobilizers or support combined with various irradiation sources originates a synergistic effect and have a significant effect on the stability and the redox properties of nZVC in the remediation process. Therefore, the review proposed that the future scope of research should include rigorous focus on deriving an exact mechanism for synergistic effect for the removal of contaminants by supported nZVC.

Cathodic Corrosion of Metal Electrodes-How to Prevent It in Electroorganic Synthesis

The critical aspects of the corrosion of metal electrodes in cathodic reductions are covered. We discuss the involved mechanisms including alloying with alkali metals, cathodic etching in aqueous and aprotic media, and formation of metal hydrides and organometallics. Successful approaches that have been implemented to suppress cathodic corrosion are reviewed. We present several examples from electroorganic synthesis where the clever use of alloys instead of soft neat heavy metals and the application of protective cationic additives have allowed to successfully exploit these materials as cathodes. Because of the high overpotential for the hydrogen evolution reaction, such cathodes can contribute toward more sustainable green synthetic processes. The reported strategies expand the applications of organic electrosynthesis because a more negative regime is accessible within protic media and common metal poisons, e.g., sulfur-containing substrates, are compatible with these cathodes. The strongly diminished hydrogen evolution side reaction paves the way for more efficient reductive electroorganic conversions.

Synthesis of Nanoparticles by Spark Discharge as a Facile and Versatile Technique of Preparing Highly Conductive Pt Nano-Ink for Printed Electronics

A cost-effective, scalable and versatile method of preparing nano-ink without hazardous chemical precursors is a prerequisite for widespread adoption of printed electronics. Precursor-free synthesis by spark discharge is promising for this purpose. The synthesis of platinum nanoparticles (PtNPs) using a spark discharge under Ar, N2, and air has been investigated to prepare highly conductive nano-ink. The size, chemical composition, and mass production rate of PtNPs significantly depended on the carrier gas. Pure metallic PtNPs with sizes of 5.5 ± 1.8 and 7.1 ± 2.4 nm were formed under Ar and N2, respectively. PtNPs with sizes of 18.2 ± 9.0 nm produced using air consisted of amorphous oxide PtO and metallic Pt. The mass production rates of PtNPs were 53 ± 6, 366 ± 59, and 490 ± 36 mg/h using a spark discharge under Ar, N2, and air, respectively. It was found that the energy dissipated in the spark gap is not a significant parameter that determines the mass production rate. Stable Pt nano-ink (25 wt.%) was prepared only on the basis of PtNPs synthesized under air. Narrow (about 30 μm) and conductive Pt lines were formed by the aerosol jet printing with prepared nano-ink. The resistivity of the Pt lines sintered at 750 °C was (1.2 ± 0.1)·10-7 Ω·m, which is about 1.1 times higher than that of bulk Pt.

Nanoscale morphological evolution of monocrystalline Pt surfaces during cathodic corrosion

Cathodic corrosion is a relatively unexplored but highly enigmatic electrochemical phenomenon that transforms, roughens, and dissolves metal surfaces under cathodic polarization. We show how cathodic corrosion of a platinum spherical single-crystal electrode in an aqueous alkaline electrolyte leads initially to the formation of etch pits that reflect the local symmetry of the surface and subsequently develop into a growth regime in which self-similar diffusion-limited patterns emerge. These are unique observations that may eventually open the door to controlled surface patterning and nanoparticle preparation.

This paper studies the cathodic corrosion of a spherical single crystal of platinum in an aqueous alkaline electrolyte, to map out the detailed facet dependence of the corrosion structures forming during this still largely unexplored electrochemical phenomenon. We find that anisotropic corrosion of the platinum electrode takes place in different stages. Initially, corrosion etch pits are formed, which reflect the local symmetry of the surface: square pits on (100) facets, triangular pits on (111) facets, and rectangular pits on (110) facets. We hypothesize that these etch pits are formed through a ternary metal hydride corrosion intermediate. In contrast to anodic corrosion, the (111) facet corrodes the fastest, and the (110) facet corrodes the slowest. For cathodic corrosion on the (100) facet and on higher-index surfaces close to the (100) plane, the etch pit destabilizes in a second growth stage, by etching faster in the (111) direction, leading to arms in the etch pit, yielding a concave octagon-shaped pit. In a third growth stage, these arms develop side arms, leading to a structure that strongly resembles a self-similar diffusion-limited growth pattern, with strongly preferred growth directions.

Top-Down Synthesis of Nanostructured Platinum-Lanthanide Alloy Oxygen Reduction Reaction Catalysts: Pt xPr/C as an Example

The oxygen reduction reaction (ORR) is of great interest for future sustainable energy conversion and storage, especially concerning fuel cell applications. The preparation of active, affordable, and scalable electrocatalysts and their application in fuel cell engines of hydrogen cars is a prominent step toward the reduction of air pollution, especially in urban areas. Alloying nanostructured Pt with lanthanides is a promising approach to enhance its catalytic ORR activity, whereby the development of a simple synthetic route turned out to be a nontrivial endeavor. Herein, for the first time, we present a successful single-step, scalable top-down synthetic route for Pt-lanthanide alloy nanoparticles, as witnessed by the example of Pr-alloyed Pt nanoparticles. The catalyst was characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and photoelectron spectroscopy, and its electrocatalytic oxygen reduction activity was investigated using a rotating disk electrode technique. Pt _xPr/C showed ∼3.5 times higher [1.96 mA/cm²_Pt, 0.9 V vs reversible hydrogen electrode (RHE)] specific activity and ∼1.7 times higher (0.7 A/mg_Pt, 0.9 V vs RHE) mass activity compared to commercial Pt/C catalysts. On the basis of previous findings and characterization of the Pt _xPr/C catalyst, the activity improvement over commercial Pt/C originates from a lattice strain introduced by the alloying process.

Alkali Metal Cation Effects in Structuring Pt, Rh, and Au Surfaces through Cathodic Corrosion

Cathodic corrosion is an electrochemical etching process that alters metallic surfaces by creating nanoparticles and a variety of etching features. Because these features typically have a preferential orientation, cathodic corrosion can be applied to modify and nanostructure electrode surfaces. However, this application of cathodic corrosion is currently limited by an insufficient chemical understanding of its underlying mechanism. This includes the role of alkali metal cations, which are thought to be crucial in both enabling cathodic corrosion and controlling its final facet preference. This work addresses this knowledge gap by exploring the cathodic corrosion of Pt, Rh, and Au in LiOH, NaOH, and KOH through both experimental and theoretical methods. These methods demonstrate that cations are adsorbed during cathodic corrosion and play a major role in controlling the onset potential and final surface morphology in cathodic corrosion. Interestingly, an equally significant role appears to be played by adsorbed hydrogen, based on calculations using literature density functional theory data. Considering the significance of both hydrogen and electrolyte cations, it is hypothesized that cathodic corrosion might proceed via an intermediate ternary metal hydride. This fundamental insight leads to both metal-specific recommendations and more general guidelines for applying cathodic corrosion to structure metallic surfaces.