Monday, 10 October 2022
In electrochemistry the reaction rate depends strongly on the voltage difference applied between the two electrodes. A voltage increase at the electrodes will generate a larger electric field in the electric double layer (EDL), which increases the reaction rate, but this will also cause additional power to be dissipated. We show both theoretically and experimentally that one can increase the electrochemical reaction rate, at no additional cost in power, by utilizing an external electric field in the proximity of a material catalyst. This is not surprising since, although the exact mechanism for catalysis due to a material compound can be quite intricate, the basic underlying physical processes for catalysis can often be shown to be due to the molecular electric field at a specific catalyst surface site. Here we generalize this observation and show how the application of a ‘simple external’ electrostatic field in conjunction with a low density-of-states conductor such as graphene can be used to intensify the already large electric field in the EDL layer - thus accelerating the reaction rate without additional power dissipation. We focus on water electrolysis (more specifically, the hydrogen evolution reaction - HER) in our electrochemical reaction study. Based on our observed experimental results as well as our theoretical analysis we show how an electrode incorporating trapped charge at the interface between two dielectrics will generate a large electrostatic field which, in conjunction with the quantum capacitance of a low density-of-states conductor, allows penetration of this field into the electric double layer (EDL), thereby adding to the original EDL field and thus, functioning as a reaction rate accelerant or a catalyst. Our experiment shows a 100% increase in the hydrogen generation rate for the HER reaction when employing our external electrostatic ‘catalyst’ technique. Since this method depends primarily on the enhancement of the EDL electric field for the reaction rate increase, it can be universally applied to all electrochemical reactions without requiring a detailed molecular level understanding of the reaction of interest.