(256f) Field-Effect Control of Electrochemical Behaviors on Graphene Electrodes

We report here the influence of the field-effect on electrochemical behaviors on graphene electrodes. First, we will show the field-effect enables direct estimation of quantum capacitance and double-layer capacitance of the graphene electrode. The Fermi-level position E_F of the electrode can be tracked by measuring its electrochemical potential with respect to a reference electrode immersed in the electrolyte phase. Thus, the potential δ required to fill the energy band of graphene with charge carriers (i.e., electrons or holes) can be directly measured from the electrochemical potential change while the carrier density in the graphene channel is independently controlled with back-gate bias. In turn, the quantum capacitance C_Q (i.e., the DOS) of graphene can be estimated from this information. Furthermore, when the carriers in the graphene channel are induced through the electrolyte-gate (i.e., the counter electrode immersed in the electrolyte phase), the potential  required to charge the electric double-layer at the graphene/electrolyte interface can be conveniently separated from δ by comparing electrochemical potentials of graphene during back- and electrolyte-gating. Furthermore, we will show the rate of electrochemical reactions on graphene surface can be controlled by the field-effect. This gate-tunable graphene electrodes are useful testbeds for understanding transport, electronic structure, and electron transfer kinetics on graphene. The approaches we follow here should also be applicable for investigating other 2D materials such as MoS₂ and ultrathin layers of conventional semiconductors.