Signal-Amplified Analysis of Molecular Layers Prepared through Bipolar Electrochemistry

Bipolar electrochemistry in synergy with electrophoresis: electric field-driven electrosynthesis of anisotropic polymeric materials

The synergistic effect of bipolar electrochemistry and electrophoresis enables facile access to various anisotropic functional materials.

Bipolar Electrochemistry: A Powerful Tool for Electrifying Functional Material Synthesis

Electrosynthesis is a powerful method for the synthesis of organic, inorganic, and polymeric materials based on electron-transfer-driven reactions at the substrate/electrode interface. The use of electricity for synthetic reactions without the need for hazardous chemical oxidants and reductants is recognized as a green and sustainable method. Other advantages include control of the reaction selectivity by tuning the electrode potentials. A different mode for driving electrochemical reactions has recently been proposed, in which bipolar electrodes (BPEs) are available as wireless electrodes that undergo anodic and cathodic reactions simultaneously. Bipolar electrochemistry is an old technology that has recently garnered renewed attention because of the interesting features of BPEs: (i) the wireless nature of a BPE is useful for sensors and material synthesis; (ii) the gradient potential distribution on BPEs is a powerful tool for the preparation of gradient surfaces and materials; and (iii) electrophoresis is available for effective electrolysis. In addition to these unique features, a BPE system only requires a small amount of supporting electrolyte in principle, whereas a large amount of electrolyte is necessary in conventional electrochemistry. Hence, bipolar electrochemistry is an inherently green and sustainable chemical process for the synthesis of materials. In this Account, recent progress in bipolar electrochemistry for the electrosynthesis of functional materials is summarized. The wireless nature of BPEs was utilized for symmetry breaking to produce anisotropic materials based on the site-selective modification of conductive objects by electrodeposition and electropolymerization. Potential gradients on a BPE interface have been successfully used as controllable templates to form molecular or polymeric gradient materials, which are potentially applicable for high throughput analytical equipment or as biomimetic materials. The electric field necessary to drive BPEs is also potentially useful to induce the directed migration of charged species. The synergetic effects of electrophoresis and electrolysis were also successfully demonstrated to obtain various functional materials. These features of bipolar electrochemistry and the various combinations of techniques have the potential to change the methodologies of material synthesis. Furthermore, the fundamental principle of bipolar electrochemistry infers that very small amounts of supporting electrolyte are necessary for an electrode system, which is expected to lead new methods of sustainable organic electrosynthesis.

Modulation of Wetting Gradients by Tuning the Interplay between Surface Structuration and Anisotropic Molecular Layers with Bipolar Electrochemistry

A new simple and versatile method for the preparation of surface-wetting gradients is proposed. It is based on the combination of electrode surface structuration introduced by a sacrificial template approach and the formation of a tunable molecular gradient by bipolar electrochemistry. The gradient involves the formation of a self-assembled monolayer on a gold surface by selecting an appropriate thiol molecule and subsequent reductive desorption by means of bipolar electrochemistry. Under these conditions, completion of the reductive desorption process evolves along the bipolar surface with a maximum strength localized at the cathodic edge and a decreasing driving force towards the middle of the surface. The remaining quantity of surface-immobilized thiol, therefore, varies as a function of the axial position, resulting in the formation of a molecular gradient. The surface of the bipolar electrode is characterized at each step of the modification by recording heterogeneous electron transfer. Also, the evolution of static contact angles measured with a water droplet deposited on the surface directly reveals the presence of the wetting gradient, which can be modulated by changing the properties of the thiol. This is exemplified with a long, hydrophobic alkane-thiol and a short, hydrophilic mercaptan.

The controlled synthesis of pillar[6]arene-based hexagonal cylindrical structures on an electrode surface via electrochemical oxidation

Electrochemical oxidation of pillar[6]arene containing six hydroquinones resulted in the formation of hexagonal cylindrical structures on an electrode surface driven by charge transfer interaction.

Closed bipolar electrode-enabled dual-cell electrochromic detectors for chemical sensing

Battery operation of a closed-BPE dual cell with colorimetric readout by smartphone camera yields a simple, inexpensive, field-deployable electrochemical sensor.