Drop cast (DC) and electrodeposited (ED) graphene-based coatings on glassy carbon (GC) electrodes were subjected to various electro-reduction degrees. The ED coatings were characterized by more accumulated graphene sheets imperfections as observed by cross section TEM analysis. These coatings, when reduced at −1.6 V vs Hg/HgO showed more efficient removal of phenolic groups than DC ones treated at the same potential (remaining contents of 2.1 and 18.1%, respectively). They also showed lower charge transfer resistance (5.2 and 28 Ω cm2, respectively), higher capacitance (73.2 and 42.6 F g−1, respectively), and higher hydrogen storage capacity (119 and 57 mAh g−1, respectively). Moreover, they showed higher stability towards H2 charge/discharge cycles (retained hydrogen capacities of 95 and 40% after 15 and 6 cycles for ED and DC coatings reduced at −1.5 V, respectively). The superior performance properties of coatings obtained by ED and subsequently electro-reduced make them promising electrode materials for energy storage.

New coatings are obtained when graphene oxide is further oxidized at moderate anodic potentials (≤~1.3 V vs. Ag/AgCl). Based on a variety of spectroscopic and electrochemical observations, the coatings are attributed to the direct electropolymerization of graphene oxide sheets via oxidation of the phenol edge groups on graphene. Depending on the applied potential, ether or carboxylic groups are formed. The coatings obtained via further oxidation are characterized by a lower O/C ratio due to decarboxylation and a higher content of C=C bonds. These bonds extend aromatic conjugation into the combined graphene oxide sheets and are responsible for the highly conductive nature of these coatings.

The voltage bias that causes a transition from direct tunneling to Fowler–Nordheim tunneling in the current-voltage characteristic of a metal/HfO2/SiO2/n-Si capacitor was measured. The transition occurs in the negative gate voltage regime and can be attributed to conduction of electrons from the metal through a defect level in the HfO2 or to conduction of holes from the Si through the valence band of the HfO2. The dependence of the determined barrier height on the gate-metal work function indicates the validity of the latter model.