(536d) Field Effect Control of Electrochemical Reaction Kinetics at Back-Gated, Ultrathin Semiconductor Electrodes

An electrochemical reaction refers to a process of chemical changes caused by the electrical current, or a process of generating electricity by chemical reactions, in which direction and rate of the reaction can be controlled by electrode potential (i.e. energy of holes and electrons in the electrode). Because an electrochemical reaction involves with charge transfer across an electrode/electrolyte interface (though it may not be the only process), the reaction kinetics is determined to a large extent by the electronic structures (i.e. energy level distribution and electronic occupation) of the electrode material and the redox species in the electrolyte. In this talk, we propose a new approach exploiting the field effect, in addition to electrode potential, to modulate the electronic structures and electrochemical reaction kinetics at electrode/electrolyte interfaces.

As a model system, we prepared working electrodes with â??gate-insulator-semiconductorâ?? structure, which is similar to that of field effect transistors (FETs). Herein, we employed ultrathin semiconductor layers so that electrochemistry at the semiconductor surface are effectively modulated by a voltage bias applied to the gate. On those gate-tunable electrodes, we observed continuous, in-situ modulation of outer-sphere electron transfer kinetics at the semiconductor/electrolyte interface with voltage biases applied to the gate. For example, the reduction potential of 2,3,5,6-tetrabromo-1,4-benzoquinone (TBBQ) on a 5 nm thick ZnO electrode could be shifted by ~0.4 V. With further control experiments, we found that the observed gate-controlled redox reaction kinetics is essentially attributed to band alignment shift at the electrode/electrolyte interface.