Electrochemical properties of metal-oxide-coated carbon electrodes prepared by atomic layer deposition.

Here we report on the electrochemical properties of carbon electrodes coated with thin layers of Al2O3 and SnO2. These oxide films were deposited using atomic layer deposition (ALD) and range in thickness from 1 to 6 nm. Electrochemical experiments show that the thinnest oxide layers contain defects that penetrate to the underlying carbon electrode.

Wire, mesh, and fiber electrodes for paper-based electroanalytical devices.

Here, we report the use of microwire and mesh working electrodes in paper analytical devices fabricated by origami paper folding (oPADs). The important new result is that Au wires and carbon fibers having diameters ranging from micrometers to tens of micrometers can be incorporated into oPADs and that their electrochemical characteristics are consistent with the results of finite element simulations. These electrodes are fully compatible with both hollow channels and paper channels filled with cellulose fibers, and they are easier to incorporate than typical screen-printed carbon electrodes.

Hollow-channel paper analytical devices.

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.

Bipolar electrochemistry.

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.

Correlated electrochemical and optical tracking of discrete collision events.

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.

Parallel screening of electrocatalyst candidates using bipolar electrochemistry.

Here we report simultaneous screening of bimetallic electrocatalyst candidates for the oxygen reduction reaction (ORR) using bipolar electrochemistry. The analysis is carried out by dispensing different bimetallic precursor compositions onto the cathodic poles of an array of bipolar electrodes (BPEs) and then heating them in a reducing atmosphere to yield the catalyst candidates. Because BPEs do not require a direct electrical connection for activation, up to 33 electrocatalysts can be screened simultaneously by applying a voltage to the electrolyte solution in which the BPE array is immersed.

Bipolar electrodes for rapid screening of electrocatalysts.

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.

Pressure-driven bipolar electrochemistry.

Here we report that pressure-driven flow alone (no external electrical energy) can be used to drive faradaic electrochemical reactions in microchannels with charged walls. Specifically, we show that solution flow can generate streaming potentials on the order of volts and that this is sufficient to carry out reactions on the anodic and cathodic poles of a bipolar electrode (BPE). The existence of faradaic reactions is proven by electrodissolution of Ag from the anodic end of the BPE.

Two-dimensional bipolar electrochemistry.

This paper introduces the concept of two-dimensional bipolar electrochemistry and discusses its principle of operation. The interesting new result is that electrochemical reactions can be localized at particular locations on the perimeter of a two-dimensional bipolar electrode (2D-BPE), configured at the intersection of two orthogonal microfluidic channels, by controlling the electric field within the contacting electrolyte solution. Experimentally determined maps of the electric field in the vicinity of the 2D-BPEs are in semiquantitative agreement with finite element simulations.