Creative approaches to the design of catalytic nanomaterials are necessary in achieving environmentally sustainable energy sources. Integrating dissimilar metals into a single nanoparticle (NP) offers a unique avenue for customizing catalytic activity and maximizing surface area. Alloys containing five or more equimolar components with a disordered, amorphous microstructure, referred to as High-Entropy Metallic Glasses (HEMGs), provide tunable catalytic performance based on the individual properties of incorporated metals. Here, we present a generalized strategy to electrosynthesize HEMG-NPs with up to eight equimolar components by confining multiple metal salt precursors to water nanodroplets emulsified in dichloroethane. Upon collision with an electrode, alloy NPs are electrodeposited into a disordered microstructure, where dissimilar metal atoms are proximally arranged. We also demonstrate precise control over metal stoichiometry by tuning the concentration of metal salt dissolved in the nanodroplet. The application of HEMG-NPs to energy conversion is highlighted with electrocatalytic water splitting on CoFeLaNiPt HEMG-NPs.

Prodigious resources are currently being devoted to control the size and morphology of metal nanoparticles (NPs). Several homogeneous chemical and photochemical techniques exist for the synthesis of metal NPs; however, these synthetic methods generally leave a distribution of NP shapes and sizes and require a stabilizing ligand to prevent aggregation. Electrodeposition of metal NPs onto conductive surfaces is a versatile technique. However, spatial control on the conductive surface is difficult to attain, even on well-behaved materials like highly oriented pyrolytic graphite. Here, we achieve spatial control of Pt NPs on amorphous graphite by confining a precursor metal salt, such as hexachloroplatinic acid (HCPA), to a water droplet suspended in oil, such as dichloroethane. When a graphite electrode was placed in solution and biased at a mild potential (−0.7 V vs the ferrocene/ferrocenium couple, Cp 2 Fe 0/+ ), droplet-mediated electrodeposition produced NPs characterized by the electrochemical collision method and scanning electron microscopy (SEM). The flux of droplets to the graphite surface followed the familiar Cottrell relationship for semiinfinite linear diffusion. Pt NP size selectivity can be directly modulated by tuning the initial concentration of HCPA in the droplet. Interestingly, the size, morphology, roughness, and coverage are shown to be influenced by the surfactant used to stabilize the water droplets, the concentration of HCPA, and the deposition potential. For instance, no surfactant, sodium dodecyl sulfate (SDS), and Span-20 generated NPs with relative roughness values of 46, 50, and 54%, respectively. Importantly, the incorporation of Span-20, a neutral emulsifier, facilitated homogeneously distributed Pt NP surface coverage on amorphous graphite, indicating the technique is apathetic to basal planes and edges of the graphite surface. The addition of SDS to droplets with large concentrations of HCPA resulted in conical and pillar-like NP morphologies, furthur enhancing surface area. The effect of deposition potential was also explored, which indicated that the roughness of the NPs can be increased by ∼10% depending on the potential. We also demonstrate that the method can be extended to the deposition of several other metal NPs, including silver, gold, copper, tin, iron, and cerium onto various substrates such as gold, silicon, boron-doped diamond (BDD), and highly oriented pyrolytic graphite (HOPG). The advantage of this technique is that size-selective electrodeposition of ligand-free, uniformly distributed NPs can be achieved.

Experimental electrochemistry offers unique opportunities for interactive instruction at all levels of education; however, widespread adoption in curricula is hindered by high costs associated with electrochemical instrumentation. Thus, the development of affordable instruments represents an essential step toward making electrochemistry accessible to everyone. While numerous commercially available three-electrode potentiostats exist, two-electrode potentiostats provide a simple and inexpensive alternative. Herein, we present the two-electrode SweepStat as a low-cost option capable of performing voltammetry and amperometry with comparable data acquisition to commercially available potentiostats valued from $4,000–40,000 USD. Additionally, the SweepStat’s design facilitates current measurements in the nanoampere regime, permitting experiments with ultramicroelectrodes (UMEs; r electrode < 25 μm). The fabrication, programming, and testing of this device constitute a valuable experimental exercise at the intersection of circuit design and construction, computer programing, and electrochemical analysis. A set of simple electrochemical experiments are presented for both macroelectrodes and UMEs, highlighting key electrochemical techniques, equations, and concepts. Furthermore, finite element modeling and commercial potentiostat comparisons are used to verify the efficacy of the SweepStat platform. The open-source nature of the SweepStat coupled with the wealth of electrochemical techniques and experiments that can be implemented with a simple two-electrode circuit offers an unparalleled opportunity for electrochemical instruction with extensive method development driven by student research.

Alcohol oxidation is an important class of reaction that is traditionally performed under harsh conditions and most often requires the use of organometallic compounds or transition metal complexes as catalysts. Here, we introduce a new electrochemical synthetic method, referred to as reductive oxidation, in which alcohol oxidation is initiated by the redox-mediated electrocatalytic reduction of peroxydisulfate to generate the highly oxidizing sulfate radical anion. Thus, and counter-intuitively, alcohol oxidation occurs as a result of an electrochemical reduction reaction. This approach provides a selective synthetic route for the oxidation of alcohols carried out under mild conditions to aldehydes, ketones, and carboxylic acids with up to 99% conversion yields. First-principles density functional theory calculations, ab initio molecular dynamics simulations, cyclic voltammetry, and finite difference simulations are presented that support and provide additional insights into the S2O8 2–-mediated oxidation of benzyl alcohol to benzaldehyde.

Measurements at the single-entity level provide more precise diagnosis and understanding of basic biological and chemical processes. Recent advances in the chemical measurement provide a means for ultra-sensitive analysis. Confining the single analyte and electrons near the sensing interface can greatly enhance the sensitivity and selectivity. In this review, we summarize the recent progress in single-entity electrochemistry of single molecules, single particles, single cells and even brain analysis. The benefits of confining these entities to a compatible size sensing interface are exemplified. Finally, the opportunities and challenges of single entity electrochemistry are addressed.