Increasing the light emission of electrogenerated chemiluminescence is an important goal for enhancing the sensitivity for potential practical applications. Electrogenerated chemiluminescence is primarily triggered by a heterogeneous electron transfer reaction, for which the electrode material plays a pivotal role. We investigated how a platinum electrode, one of the most used but poorly efficient noble metal electrode materials in electrogenerated chemiluminescence, can be modified to enhance light emission. A polypyrrole layer was deposited on the platinum electrode through electrochemically induced polymerization, and subsequently pyrolyzed with the formation of a carbonaceous film. Electrochemiluminescence of the [Ru(bpy)(3)](2+)/tri-n-propylamine system on such carbon film electrodes showed an enhancement of up to a 4 times increase, as compared with the bare platinum electrode.

The Scanning Bipolar Electrochemical Microscope (SBECM) allows precise positioning of an electrochemical micro-probe serving as bipolar electrode that can be wirelessly interrogated by coupling the electrochemical detection reaction with an electrochemiluminescent reporting process. As a result, the spatially heterogeneous concentrations of an analyte of interest can be converted in real time into a map of sample reactivity. However, this can only be achieved upon optimization of the analytical performance ensuring adequate sensitivity. Here, we present the evaluation and optimized operation of the SBECM for the detection of small changes in local O2 concentrations. Parameters for achieving an improved sensitivity as well as possibilities for improving the signal-to-noise ratio in the optical signal readout are evaluated. The capability of the SBECM for O2 detection is shown at controlled conditions by recording the topography of a patterned sample and monitoring O2 evolution from a photoelectrocatalyst material.

Electrochemical techniques offer high temporal resolution for studying the dynamics of electroactive species at samples of interest. To monitor fastest concentration changes, a micro- or nanoelectrode is accurately positioned in the vicinity of a sample surface. Using a microelectrode array, it is even possible to investigate several sites simultaneously and to obtain an instantaneous image of local dynamics. However, the spatial resolution is limited by the minimal electrode size required in order to contact the electrodes. To provide a remedy, we introduce the concept of scanning bipolar electrochemical microscopy and the corresponding experimental system. This technique allows precise positioning of a wireless scanning bipolar electrode to convert spatially heterogeneous concentrations of the analyte of interest into an electrochemiluminescence map of the sample reactivity. After elucidating the working principle by recording bipolar line and array scans, a bipolar electrode array is positioned at the site of interest to record an electrochemical image of the localized release of analyte molecules.

Surface-enhanced Raman spectroscopy is a powerful analytical tool and a strongly surface structure-dependent process. Importantly, it can be coupled with electrochemistry to simultaneously record vibrational spectroscopic information during electrocatalytic reactions. Highest Raman enhancements are obtained using precisely tuned nanostructures. The fabrication and evaluation of a high number of different nanostructures with slightly different properties is time-consuming. We present a strategy to systematically determine optimal nanostructure properties of electrochemically generated Ag void structures in order to find the void size providing highest signal enhancement for Raman spectroscopy. Ag-coated Si wafers were decorated with a monolayer of differently sized polymer nanospheres using a Langmuir-Blodgett approach. Subsequently, bipolar electrochemistry was used to electrodeposit a gradient of differently sized void structures. The gradient structures were locally evaluated using Raman spectroscopy of a surface-adsorbed Raman probe, and the surface regions exhibiting the highest Raman enhancement were characterized by means of scanning electron microscopy. High-throughput scanning droplet cell experiments were utilized to determine suitable conditions for the electrodeposition of the found highly active structure in a three-electrode electrochemical cell. This structure was subsequently employed as the working electrode in operando surface-enhanced Raman measurements to verify its viability as the signal amplifier and to spectroscopically rationalize the complex electrochemical reduction of carbon dioxide.

Rotation of a bipolar electrode in a constant electric field between feeder electrodes causes an alternating bipolar current at an AC frequency that depends on the rotation rate. The corresponding oscillation of the feeder current is evaluated by means of a lock-in amplifier. This innovative approach allows the current flowing through the non-wired bipolar electrode in an open bipolar system to be extracted without relying on electrochemical reporter reactions.

Bipolar electrochemistry has been shown to enable and control various kinds of propulsion of nonwired conducting objects: translation, rotation, and levitation. There is a very rapid development in the field of controlled motion combined with other functionalities. Here we integrate two different concepts in one system to generate wireless electrochemical motion of a specifically designed rotor and track its polarization simultaneously by electrochemical light emission. Locally produced hydrogen bubbles at the cathodic pole of the bipolar rotor are the driving force of the motion, whereas [Ru(bpy)3]Cl2 and tripropylamine react at the anodic extremity, thus generating an electrochemiluminescence signal with an intensity directly correlated with the orientation of the rotor arms. This allows in a straightforward way the qualitative visualization of the changing interfacial potential differences during rotation and shows for the first time that light emission can be coupled to autonomously rotating bipolar electrodes.

Electrochemical communication between two photobioelectrochemical half-cells based on photosystem 1 and photosystem 2 is investigated in operando. The driving force for the electron-transfer reactions is applied in a wireless mode using bipolar electrochemistry with the actual electrode potentials being self-regulated by the redox processes. Four parameters are assessed to understand the overall performance and elucidate the limiting reactions of the photobioelectrochemical cell. In addition to the potential differences for oxidation and reduction reactions, the current flowing between the half-cells as well as in situ collection of locally evolved O2 by photosystem 2 using a positioned scanning electrochemical microscopy tip are evaluated. In this way, changes in the enzymatic performances as a result of inactivation of either of the protein complexes or variations in the external conditions are monitored.

Electrochemical efficiency and stability are among the most important characteristics of electrocatalysts. These parameters are usually evaluated separately for the anodic and cathodic half-cell reactions in a three-electrode system or by measuring the overall cell voltage between the anode and cathode as a function of current or time. Here, we demonstrate how bipolar electrochemistry can be exploited to evaluate the efficiency of electrocatalysts for full electrochemical water splitting while simultaneously and independently monitoring the individual performance and stability of the half-cell electrocatalysts. Using a closed bipolar electrochemistry setup, all important parameters such as overvoltage, half-cell potential, and catalyst stability can be derived from a single galvanostatic experiment. In the proposed experiment, none of the half-reactions is limiting on the other, making it possible to precisely monitor the contribution of the individual half-cell reactions on the durability of the cell performance. The proposed approach was successfully employed to investigate the long-term performance of a bifunctional water splitting catalyst, specifically amorphous cobalt boride (Co2B), and the durability of the electrocatalyst at the anode and cathode during water electrolysis. Additionally, by periodically alternating the polarization applied to the bipolar electrode (BE) modified with a bifunctional oxygen electrocatalyst, it was possible to explicitly follow the contributions of the oxygen reduction (ORR) and the oxygen evolution (OER) half-reactions on the overall long-term durability of the bifunctional OER/ORR electrocatalyst.

As surface-enhanced Raman scattering (SERS) crucially depends on the morphology of nanostructured metal surfaces, we developed a convenient approach to produce a size gradient of truncated spherical Au nanovoids on a single bipolar electrode. The continuous potential drop in solution implies a linearly changing interfacial potential difference at the wireless electrode, leading to a linearly changing rate of Au electrodeposition. Such a structural gradient enables fast and reproducible screening for those structures, evoking high SERS intensity in a particular experiment. The optimal Au deposition potential with respect to the highest SERS amplification was determined and applied for the fabrication of highly active SERS substrates.

The range of potential analytes for bipolar electrochemistry can be significantly extended by modification of bipolar electrodes with enzymatic biosensing layers. In this study, we employed a Prussian blue-based glucose detection system involving electrochemical reduction of enzymatically generated hydrogen peroxide at the cathodic pole. The concentration of glucose in solution can be correlated with oxidative luminol electrochemiluminescence at the opposite anodic pole, which was recorded with a photomultiplier tube. This opens a route for novel analytical systems using glucose oxidase as an amplification element for the reporter reaction.

The majority of efforts on microbial and photosynthetic microbial fuel cells are both curiosity driven and made to possibly meet the future growing demand for sustainable energy. The most metabolically versatile purple bacteria Rhodobacter capsulatus is a potential candidate for this purpose. However, utilizing bacteria in such systems requires efficient electronic transfer communication between the microbial cells and the electrodes, which is one of the greatest challenges. Previous studies demonstrated that osmium redox polymers (ORPs) could be used for extracellular electron transfer between the cells and electrodes. Recently, heterotrophically grown R. capsulatus has been wired with ORP modified electrodes. Here in this communication, we report electron transfer from R. capsulatus grown under heterotrophic as well as under photoheterotrophic conditions to electrodes. The cells, immobilized on bare graphite and ORP modified graphite electrodes, were excited with visible light and subsequent photosynthetic electron transfer was recorded using cyclic voltammetric and chronoamperometric measurements. Photoheterotrophically grown R. capsulatus cells on bare graphite generate a significant photocurrent density of 3.46 mu A cm(-2), whereas on an ORP modified electrode the current density increases to 8.46 mu A cm(-2). Furthermore, when 1 mM p-benzoquinone is added to the electrolyte the photocurrent density reaches 12.25 mu A cm(-2). Our results could have significant implications in photosynthetic energy conversion and in development of photobioelectrochemical devices.