Single entity electrochemistry and the electron transfer kinetics of hydrazine oxidation

The mechanism and kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.

Unveiling the intrinsic properties of single NiZnFeO_x entity for promoting electrocatalytic oxygen evolution

Although considerable research efforts have been devoted to the design and development of non-noble electrocatalysts for oxygen evolution reaction(OER), substantial enhancement of OER performance with commercial-scale water electrolysis remains a big challenge. This could result from the difficulties in detecting the intrinsic properties and overlooking the assembly process for electrochemical OER process. Here, we employ a microjet collision method to investigate the intrinsic OER activities of individual NiZnFeO_x entities with and without a moderate magnetic field. Our results demonstrate that single NiZnFeO_x nanoparticles(NPs) show the excellent OER performance with a lowest onset potential(~1.35 V vs. RHE) and a greatest magnetic enhancement(~118%) among bulk materials, single agglomerations and NPs. Furthermore, we explore the utility of theoretical investigation by density functional theory(DFT)calculations for studying OER process on NiZnFeO_x surfaces without and with spin alignment, indicating monodispersed NiZnFeO_xNPs with totally spin alignment facilitates the OER process under the external magnetic field. It is found that the well-dispersion of NiZnFeO_x NPs would increase the electrical conductivity and the surface spin state, resulting in promoting their OER activities. This work provides a test for uncovering the essential roles of NPs assembly to a significant promotion of their magnet-assisted OER.

Single-entity electrochemistry at confined sensing interfaces

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.

High-density single antibody electrochemical nanoarrays

The fabrication and electrochemical interrogation of very high density single-antibody nanoarrays is reported.Gold nanodots,15 nm in diameter,arranged in large(cm2)square arrays with a pitch of 200 nm,are used as carriers for primary antibodies(immunoglobulin G(IgG)),further recognized by secondary redox-labeled detection antibodies.Ensemble scale interrogation of the antibody array by cyclic voltammetry,and nanoscale interrogation of individual nanodots by mediator tethered atomic forcescanning electrochemical microscopy(Mt/AFM-SECM),enable the occupancy of nanodots by single antibody molecules to be demonstrated.Experiments involving the competitive adsorption of antibodies of different species onto the nanodots evidence the possibility of using single-antibody nanoarrays for digital electrochemical immunoassays.

Recent advances in nanocollision electrochemistry

Ensemble averaging measurements obscure the link between the electrochemical performance and the specific properties of an individual because of the interplay of inhomogeneity and heterogeneity.Nanocollision electrochemistry has attracted increasing interest because of its extremely high sensitivity,revealing the intrinsic properties of individual entities that are masked in the traditional ensemble measurements.In this perspective review,we summarized the recent developments in nanocollision-based single entity electrochemistry and photoelectrochemistry,the combined nanocollision electrochemistry with the other complementary techniques,as well as accurate data process.In closing,future challenges,opportunities,and destinations related to nanocollison electrochemistry were discussed.

Calibrating SECCM measurements by means of a nanoelectrode ruler.The intrinsic oxygen reduction activity of PtNi catalyst nanoparticles

Scanning electrochemical cell microscopy(SECCM)is increasingly applied to determine the intrinsic catalytic activity of single electrocatalyst particle.This is especially feasible if the catalyst nanoparticles are large enough that they can be found and counted in post-SECCM scanning electron microscopy images.Evidently,this becomes impossible for very small nanoparticles and hence,a catalytic current measured in one landing zone of the SECCM droplet cannot be correlated to the exact number of catalyst particles.We show,that by introducing a ruler method employing a carbon nanoelectrode decorated with a countable number of the same catalyst particles from which the catalytic activity can be determined,the activity determined using SECCM from many spots can be converted in the intrinsic catalytic activity of a certain number of catalyst nanoparticles.