Langmuir–Blodgett\nDeposition of Graphite Oxide\nNanosheets as Catalysts for Bipolar Membrane Electrochemistry

Graphite oxide (GO) has been widely studied as an interfacial\nlayer\nin bipolar membranes because of its activity as a catalyst for the\nwater dissociation and acid–base neutralization reactions.\nHowever, the roles of GO nanosheet size, orientation, and surface\ncoverage in controlling its catalytic activity are not well understood.\nGO nanosheets with lateral dimensions of several microns were prepared\nby oxidative exfoliation of natural graphite crystals, enabling their\norientation and coverage to be observed directly by optical microscopy.\nThe coverage and orientation of the GO nanosheets were measured as\na function of different deposition methods, which included solution\nadsorption, Langmuir–Blodgett transfer from an air–water\ninterface, and spray-coating. Highly oriented GO films made by the\nLangmuir–Blodgett method gave the best performance metrics.\nInterestingly, full coverage of the bipolar interface by GO nanosheets\nresulted in lower performance than partial coverage. This effect could\nbe rationalized in terms of the differential permeability of H<sup>+</sup> and OH<sup>–</sup> ions through GO, which leads to\nconcentration polarization of OH<sup>–</sup> on one side of\nthe sheets.