Plasmas interacting with liquids enable the generation of a highly reactive interfacial liquid layer due to a variety of processes driven by plasma-produced electrons, ions, photons, and radicals. These processes show promise to enable selective, efficient, and green chemical transformations and new material synthesis approaches. While many differences are to be expected between conventional electrolysis and plasma–liquid interactions, plasma–liquid interactions can be viewed, to a first approximation, as replacing a metal electrode in an electrolytic cell with a gas phase plasma. For this reason, we refer to this method as plasma-driven solution electrochemistry (PDSE). In this Perspective, we address two fundamental questions that should be answered to enable researchers to make transformational advances in PDSE: How far from equilibrium can plasma-induced solution processes be driven? and What are the fundamental differences between PDSE and other more traditional electrochemical processes? Different aspects of both questions are discussed in five sub-questions for which we review the current state-of-the art and we provide a motivation and research vision.

Bimetallic nanoparticles formed of poorly miscible alloys are attractive for applications in surface-enhanced Raman scattering (SERS), as they could allow the detection and study of analytes that do not bind well to typical plasmonic substrates, particularly important biomolecules such as serotonin. Despite their potential importance for SERS applications, the plasmonic and geometric properties of these alloys are not well characterized. Here, we present a method for calculating the thermodynamically minimized geometries of these nanoparticles as a function of their surface, bulk, and metallic phase interface energies. We show how the geometry varies as a function of composition, from core–shell, to Janus, to phase-separated, and discuss the importance of accurately modeling the metallic phase interface region to capture particle geometries. Finally, we use the calculated Janus geometries for the AuNi and AgNi systems to explore the suitability of these particles for use in SERS and identify the ideal compositions to maximize local field enhancement on the Ni-rich phase of the particle using the finite-difference time-domain method.

The oxidation state (OS) concept is arguably one of the most useful formalisms in chemistry. OSs are used to explain catalytic behavior at a variety of transition metal (TM) centers.[1] They are also used to interpret a wide variety of spectroscopic results, such as the structure of electron paramagnetic resonance, UV-visible, and Mössbauer spectra.[2, 3] More broadly, the OS concept aids in categorizing the behavior of TMs in a general way, enabling its use as both a predictive and postdictive tool in chemical reactions. Indeed, inorganic chemists still use the masterfully organized-often by OS-tome, Advanced Inorganic Chemistry, as a way of rationalizing the chemistry of TM complexes.[4] However, while tremendously useful from a categorization perspective, the OS concept continues to inspire debate within the chemical community.[5-10] Recent exchanges show just how far the debate has gone: two competing points of view

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In plasma-driven solution electrolysis (PDSE), gas-phase plasma-produced species interact with an electrolytic solution to produce, for example, nanoparticles. An atmospheric pressure plasma jet (APPJ) directed onto a liquid solution containing a metallic salt will promote reduction of metallic ions in solution, generating metallic clusters that nucleate to form nanoparticles. In this article, results from a computational investigation are discussed of a PDSE process in which a radio-frequency APPJ sustained in helium impinges on a silver nitrate solution, resulting in growth of silver nanoparticles. A reaction mechanism was developed and implemented in a global plasma chemistry model to predict nanoparticle growth. To develop the reaction mechanism, density functional theory was used to generate probable silver growth pathways up to Ag9. Neutral clusters larger than Ag9 were classified as nanoparticles. Kinetic reaction rate coefficients for thermodynamically favorable growth pathways were estimated based on an existing, empirically determined base reaction mechanism for smaller Ag particle interactions. These rates were used in conjunction with diffusion-controlled reaction rate coefficients that were calculated for other Ag species. The role of anions in reduction of Ag n ions in forming nanoparticles is also discussed. Oxygen containing impurities or admixtures to the helium, air entrainment into the APPJ, and dissociation of saturated water vapor above the solution can produce additional reactive oxygen species in solution, resulting in the production of anions and [Formula: see text] in particular. For a given molarity, delivering a sufficient fluence of reducing species will produce similar nanoparticle densities and sizes for all applied power levels. Comparisons are made to alternate models for nanoparticle formation, including charged nanoparticles and use of direct current plasmas.