Critical Review—The Versatile Plane Parallel Electrode Geometry: An Illustrated Review

The features of the plane parallel geometry are reviewed since this cell geometry occupies a prominent position, both in the laboratory and in industry. The simple parallel plate can be enhanced by inclusion of porous, 3D electrodes, structured surfaces and bipolar electrical connections, with adequate attention to the reaction environment. Unit cells are often arranged in a modular, filter-press format. Scale-up is achieved by increasing the size of each electrode, the number of electrodes in a stack or the number of stacks in a system. The use of turbulence promoters in the flow channel, textured (including nanostructured) and porous electrodes as well as cell division by an ion exchange membrane can considerably widen the scope of the plane parallel geometry. Features of plane parallel cell designs are illustrated by selected examples from our laboratories and industry, including a fuel cell, an electrosynthesis cell and hybrid redox flow cells for energy storage. Recent trends include the development of microflow cells for electrosynthesis, 3D printing of fast prototype cells and a range of computational models to simulate reaction environment and rationalise performance. Future research needs are highlighted.