Highly efficient electro-generation of H2O2 by adjusting liquid-gas-solid three phase interfaces of porous carbonaceous cathode during oxygen reduction reaction

Abstract

Equilibrium of three reactants (oxygen, proton and electron) in oxygen reduction reaction at large current flux is necessary for highly efficient electro-generation of H₂O₂. In this work, we investigated reactants equilibrium and H₂O₂ electrochemical production in liquid-gas-solid three phase interfaces on rolling cathodes with high electroactive area. Electrocatalytic reaction accelerated the electrolyte intrusion into hydrophobic porous catalyst layer for higher electroactive surface area, resulting in a 21% increase of H₂O₂ yield at 15 mA cm^-2. Air aerated cathode submerged in air/O₂ aeration solution was unable to produce H₂O₂ efficiently due to the lack of O₂ in three phase interfaces (TPIs), especially at current density > 2.5 mA cm^-2. For air breathing cathode, stable TPIs inside the active sites was created by addition of gas diffusion layer, to increase H₂O₂ production from 11 ± 2 to 172 ± 11 mg L^-1 h^-1 at 15 mA cm^-2. Pressurized air flow application enhanced both oxygen supply and H₂O₂ departure transfer to obtain a high H₂O₂ production of 461 ± 11 mg L^-1 h^-1 with CE of 89 ± 2% at 35 mA cm^-2, 45% higher than passive gas transfer systems. Our findings provided a new insight of carbonaceous air cathode performance in producing H₂O₂, providing important information for the practical application and amplification of cathodes in the future.

Keywords: Air breathing cathode; H(2)O(2) electrocatalysis; Oxygen reduction reaction; Three phase interfaces.