Reduction of graphene oxide flakes by treatment with non-equilibrium hydrogen plasma–review and challenges

Abstract Graphene oxide (GO) is a standard precursor for the synthesis of porous yet densely packed, graphene-like structures in films with a thickness of several micrometers, which are useful for electrodes in various electrochemical devices, such as supercapacitors, as well as for various sensors. As-synthesized GO films exhibit inadequate electrical conductivity because of a large concentration of oxygen chemically bonded to graphene sheets. Heating of GO films in a non-oxidizing atmosphere will cause thermal decomposition of GO by desorption of carbon oxides, which will result in numerous defects in the sheets and partial collapsing of the sheets. An alternative is the treatment of GO films with non-equilibrium hydrogen plasma, which causes reduction rather than decomposition of the GO sheets. The scientific literature on approaches to reducing GO samples by treatment with hydrogen plasma is reviewed, the results are critically evaluated, and the correlations between the reduction efficiency and processing parameters are drawn. Paradoxically, larger discharge powers lead to worse results, both in terms of the remaining oxygen concentration and electrical properties. A feasible explanation for this paradox is radiation damage, which is likely caused by energetic photons or ions. The recommendation for further experiments in this tremendously promising niche is also presented.