Electrochemical water splitting is a promising technology to renewably generate hydrogen fuel from water. One particular drawback of conventional water splitting is that the hydrogen-forming reduction reaction is tightly coupled,...

The sensitivity of amperometric sensors is typically set by the rate diffusion of the analyte to the electrode surface, so determining diffusion coefficients in various electrolyte solutions is of fundamental interest. It has been theoretically shown and verified that diffusion coefficients of electrochemically generated analytes can be determined using electrochemical time of flight (ETOF), a method that uses an electrochemical array in which one electrode generates a Red/Ox species, and measures the analyte diffusion times to collecting electrodes of differing distances from a stationary generator. ETOF has the potential to greatly simplify the determination of diffusion coefficients as the analyte concentration, the electroactive area, the solution viscosity, and the electron transfer kinetics can remain unknown. Here we demonstrate an alternative data treatment for ETOF in which the electrochemical flight time is measured for a series of different Red/Ox species of known diffusion coefficients at a single distance. We show this a valid application of a method that has existed for almost 30 years, by determining diffusion coefficients for ruthenium (II) hexamine, and diffusion coefficients in solutions of increased viscosity. Diffusion coefficients are important because they set the sensitivity of amperometric sensors and they are a fundamental property both in membrane permeability and in electrochemical measurements. The most common method of determining diffusion coefficients for analytes in bulk solutions or through gels and membranes relies on the rotating disk electrode (RDEs) 1-7 or the rotating ring disk electrode (RRDE).8 This method determines the diffusion coefficients, D, from the slope of a Levich plot constructed by measuring limiting currents, I L , as a function of square root of the rotation rate, w, according to the Levich equation (Equation 1).Accurate values for the area of the electrode, A, the number of electrons transferred, n, the concentration of the molecule, C, and the viscosity of the solution, v, must also be known in order to effectively determine the diffusion coefficient from the slope of a Levich Plot. The diffusion coefficients of molecules through bulk solution can also be determined quantitatively by wall-jet chronoamperometry, 9 or qualitatively by comparing the CV's of different compounds because the shape of the CV is related to the diffusion coefficient of the molecule. [10][11][12] The other primary option for determining diffusion coefficients of a molecule through a membrane coated over an electrode is impedance spectroscopy, [13][14][15][16][17][18] where the diffusion of the molecule through a membrane or polymer is related to the impedance of the polymer or membrane to current flow. As such, the diffusion through the polymer is related directly to the resistance of charge transfer (mobility) through the membrane, which is related to its conductivity and directly correlated to the diffusion coefficient by the Nernst-Einstein equation (Equation 2).Conductance, σ, ca...

We report herein that synergistic light absorption in the optical near-field enables nanoscale self-organization during inorganic phototropic growth. Se−Te was grown electrochemically under illumination from an incoherent, unstructured light source in geometrically constrained, wavelength scale areas. Despite the limited dimensions, with as few as two discrete features produced in a single sub-micron dimension, the deposit morphology exhibited defined order and anisotropy. Computer modeling analysis of light absorption in simulated structures revealed a synergy wherein light capture in a nanoscale feature was enhanced by the presence of additional adjacent features, with the synergistic effect originating predominantly from nearest neighbor contributions. Modeling moreover indicated that synergistic absorption is produced by scattering of the incident illumination by individual nanoscale features, leading to a local increase in the near-field intensity and consequently increasing the absorption in neighboring features. The interplay between these optical processes establishes the basis for spontaneous order generation via inorganic phototropic growth.

Photoelectrochemical deposition of Se−Te on isolated Au islands using an unstructured, incoherent beam of light produces growth of Se−Te alloy toward the direction of the incident light beam. Full-wave electromagnetic simulations of light absorption indicated that the induced spatial growth anisotropy was a function of asymmetric absorption in the evolving deposit. Inorganic phototropic growth is analogous to biological systems such as palm trees that exhibit phototropic growth wherein physical extension of the plant guides the crown toward the time-averaged position of the sun, to maximize solar harvesting. Communication pubs.acs.org/JACS

Inorganic phototropic growth, a maskless, lithography-free process, enabled generation of CdSe films with highly ordered, optically-defined nanotextures over macroscale areas.