The widespread application of silver in consumer products and the resulting contamination of natural environments with silver raise questions about the toxicity of Ag+ in the ecosystem. Natural organic matter, NOM, which is abundant in water supplies, soil, and sediments, can form stable complexes with Ag+, altering its bioavailability and toxicity. Herein, the extent and kinetics of Ag+ binding to NOM, matrix effects on Ag+ binding to NOM, and the effect of NOM on Ag+ toxicity to Shewanella oneidensis MR-1 (assessed by the BacLight viability assay) were quantitatively studied with fluorous-phase Ag+ ion-selective electrodes (ISEs). Our findings show fast kinetics of Ag+ and NOM binding, weak Ag+ binding for Suwannee River humic acid, fulvic acid, and aquatic NOM, and stronger Ag+ binding for Pony Lake fulvic acid and Pahokee Peat humic acid. We quantified the effects of matrix components and pH on Ag+ binding to NOM, showing that the extent of binding greatly depends on the environmental conditions. The effect of NOM on the toxicity of Ag+ does not correlate with the extent of Ag+ binding to NOM, and other forms of silver, such as Ag+ reduced by NOM, are critical for understanding the effect of NOM on Ag+ toxicity. This work also shows that fluorous-phase Ag+ ISEs are effective tools for studying Ag+ binding to NOM because they can be used in a time-resolved manner to monitor the activity of Ag+ in situ with high selectivity and without the need for extensive sample preparation.

Catalytic MoS x thin films have been directly photoelectrodeposited on GaInP2 photocathodes for stable photoelectrochemical hydrogen generation. Specifically, the MoS x deposition conditions were controlled to obtain 8–10 nm films directly on p-GaInP2 substrates without ancillary protective layers. The films were nominally composed of MoS2, with additional MoO x S y and MoO3 species detected and showed no long-range crystalline order. The as-deposited material showed excellent catalytic activity toward the hydrogen evolution reaction relative to bare p-GaInP2. Notably, no appreciable photocurrent reduction was incurred by the addition of the photoelectrodeposited MoS x catalyst to the GaInP2 photocathode under light-limited operating conditions, highlighting the advantageous optical properties of the film. The MoS x catalyst also imparted enhanced durability toward photoelectrochemical hydrogen evolution in acidic conditions, maintaining nearly 85% of the initial photocurrent after 50 h of electrolysis. In total, this work demonstrates a simple method for producing dual-function catalyst/protective layers directly on high-performance, planar III–V photoelectrodes for photoelectrochemical energy conversion.

Semiconductor ultramicroelectrodes (SUMEs) were prepared by photolithographic patterning of defined pinholes in dielectric coatings on semiconductor wafers. Methods are reported for interpreting their electrochemical response characteristics in the absence of illumination. Radial diffusion is reconciled with the diode equation to describe the full voltammetric response, allowing direct determination of heterogeneous charge-transfer rate constants and surface quality. The voltammetric responses of n-type Si SUMEs were assessed and showed prototypical UME characteristics with obtainable current densities higher than those of conventional macroscopic electrodes. The SUME voltammetry proved highly sensitive to both native and intentionally grown oxides, highlighting their ability to precisely track dynamic surface conditions reliably through electrochemical measurement. Subsequently, electron transfer from the conduction band of n-Si SUMEs to aqueous Ru­(NH3)6 3+ was determined to occur near optimal exoergicity. In total, this work validates the SUME platform as a new tool to study fundamental charge-transfer properties at semiconductor/liquid junctions.

Crystalline germanium (Ge) micro-and nanowires have been grown from aqueous electrolytes through an electrochemical liquid-liquid-solid (ec-LLS) process using eutectic bismuth indium (e-BiIn) alloy as the liquid metal electrode. This alloy represents the first non-Hg or non-Ga containing liquid metal to be used for the growth of a group IV semiconductor crystal below the boiling point of water. The electrochemical stability of e-BiIn in aqueous electrolyte was assessed through cyclic voltammetry, which showed the metal alloy was destabilized either by anodic oxidation at potentials more positive than −1.0 V vs E(Ag/AgCl) or by cathodic reduction of Bi to BiH 3 at potentials more negative than −1.4 V vs E(Ag/AgCl). Within this potential window, ec-LLS produced Ge micro-and nanowires that were evaluated with scanning electron microscopy, high resolution transmission electron microscopy, and selected area electron diffraction. The cumulative analyses showed pronounced crystallinity in the as-prepared Ge microwires and nanowires, with nanowires showing an unexpected coiled morphology. Atom probe tomography data showed some incorporation of In and Bi at 6 and 3 at. %, respectively. The tomography data further demonstrated that the distribution of the metals was not uniform, as In-rich clusters were observed. A high doping character in the as-prepared Ge nanowires was separately confirmed with two-terminal resistivity measurements. In total, this work not only identifies a new liquid metal type that is amenable for ec-LLS but also suggests strongly that the composition of the liquid metal influences the resultant crystal size, shape, and purity.

A thorough framework for how to interpret and predict the steady-state voltammetric responses of semiconductor ultramicroelectrodes (SUMEs) has been compiled. Through consideration of the Marcus–Gerischer treatment for heterogeneous charge transfer and the interplay between the fractions of the applied potential that drop across the space-charge region, the solution, and their interface in depletion and accumulation conditions, the complex potential dependences of the majority carrier densities, n s, and the rate constant for electron transfer from the conduction band edge, k et, are identified. Incorporation of these terms in the conventional fitting procedures of steady-state voltammetry at inlaid disk electrodes affords determination of the full J–E responses of n-type SUMEs in a variety of experimental permutations. Working curves are presented to illustrate how the specific values of the conduction band edge potential, the reorganization energy for charge transfer, the standard potential of the redox species, and the doping density control the form of the voltammetric responses of a pristine semiconductor/electrolyte interface. Further working curves are provided to highlight the expected influence of surface states on the steady-state voltammetry of SUMEs. An example of how to analyze experimental data without the use of “non-ideality” factors is shown, illustrating that it is possible to extract validated estimates of heterogeneous charge-transfer constants and the defect character of the semiconductor/electrolyte interface. In total, this work provides a clear guide for utilizing simple, raw voltammetric data from SUMEs to study semiconductor/electrolyte contacts of interest.