A bipolar electrode (BPE) is an electrically conductive material that promotes electrochemical reactions at its extremities (poles) even in the absence of a direct ohmic contact. More specifically, when sufficient voltage is applied to an electrolyte solution in which a BPE is immersed, the potential difference between the BPE and the solution drives oxidation and reduction reactions. Because no direct electrical connection is required to activate redox reactions, large arrays of electrodes can be controlled with just a single DC power supply or even a battery. The wireless aspect of BPEs also makes it possible to electrosynthesize and screen novel materials for a wide variety of applications. Finally, bipolar electrochemistry enables mobile electrodes, dubbed microswimmers, that are able to move freely in solution.

Optical tracking of collisions between insulating microbeads and an ultramicroelectrode surface are correlated to electrochemical measurements and 3D simulations. The experiments are based on partial blocking of the electrode surface by the beads. Results obtained using these three methods provide details regarding the radial distribution of landing locations, the extent of current blockage, collision frequency, motion of beads on the electrode surface following collisions, and aggregation behavior both prior to collisions and afterward on the electrode surface.

We report a method for rapid screening of arrays of electrocatalyst candidates. The approach is based on simultaneous activation of the oxygen reduction reaction (ORR) and Ag electrodissolution at the cathodic and anodic poles, respectively, of bipolar electrodes (BPEs). Because the electrochemical activity of the two poles is directly coupled via the BPE, the extent of Ag electrodissolution is directly related to the ORR activity. The screening process lasts ∼12 min. Because Ag dissolution provides a permanent record of catalyst activity, the screening results can be determined by simple optical microscopy after the electrochemical experiment. The method has the potential to provide quantitative information about electrocatalyst activity.H ere we report a new and potentially powerful method for rapid screening of electrocatalysts. The principle is illustrated in Scheme 1, with specific reference to evaluation of the activity of electrocatalysts for the oxygen reduction reaction (ORR). The top frame of Scheme 1a shows an array of three bipolar electrodes (BPEs). 1 The ORR electrocatalyst candidates are deposited onto the cathodic poles of the BPEs, while the anodic poles are composed of parallel Ag microband electrodes. The Ag microbands of each electrode are in electrical contact with one another and with the ORR catalyst via an underlying indium-doped tin oxide (ITO) contact. When a sufficiently high potential (E tot , Scheme 1b) is applied to the solution in the fluidic channel via a pair of driving electrodes, the ORR proceeds at the cathodic poles and the Ag microbands undergo electrodissolution. 2 The efficiency of the ORR catalyst is then determined by counting the number of dissolved Ag microband electrodes: the more bands that dissolve, the better the catalyst. In fact, as we will show, there is a direct thermodynamic link between the overpotential required for the ORR (Scheme 1c) and the number of Ag microbands remaining after the experiment (Scheme 1a). Although we demonstrate this screening method using just three BPEs, arrays of arbitrary size can be monitored in this way with very little additional technological overhead. This is because it is not necessary to make a direct electrical connection to each electrode, which is an intrinsic property of BPEs and the principal reason for using them in an array format. 3 The basic operating principles of BPEs, along with many interesting applications, have been previously described in the scientific literature. 1−14 A driving voltage E tot applied across a microchannel containing a conductive electrolyte solution (Scheme 1b) is dropped nearly linearly over the length of the microchannel. 6 If a conductive wire of sufficient length is present in the microchannel, it will function as a BPE. 1 Specifically, when the interfacial potential differences between the poles of the BPE and the electrolyte solution (ΔE elec , Scheme 1a) are sufficiently high, faradaic processes occur simultaneously: a reduction at the cathodic pole and an oxidation at the a...

We present a microfluidic paper analytical device (μPAD) that relies on flow in hollow channels, rather than through a cellulose network, to transport fluids. The flow rate in hollow channels is 7 times higher than in regular paper channels and can be conveniently controlled from 0 to several mm/s by balancing capillary and pressure forces. More importantly, the pressure of a single drop of liquid (~0.2 mbar) is sufficient to induce fast pressure-driven flow, making hollow channels suitable for point of care diagnostics. We demonstrate their utility for simple colorimetric glucose and BSA assays in which the time for liquid transport is reduced by a factor of 4 compared to normal cellulose channels.

Here, we report the development of a parallel electrocatalyst screening platform for the hydrogen evolution reaction (HER) using bipolar electrodes (BPEs). Electrocatalyst candidates are subjected to screening in a N 2 -purged bipolar electrochemical cell where a pair of driving electrodes produce an electric field in the electrolyte solution. The HER occurring at the BPE cathodes is electrically coupled to the electrodissolution of an array of Cr microbands present at the BPE anodes. The readout of this device is simple, where the species that dissolve the most Cr microbands are identified as the most promising electrocatalyst candidates for further evaluation. We demonstrate the utility of this technique by comparing several bi-and trimetallic systems involving Co, Fe, Ni, Mo, and W, which are compared directly with pure Pt. Of all the compositions tested, Ni 8 −Mo 2 is demonstrated to be the most active for the HER in a neutral electrolyte solution.