Direct reduction of oxygen gas over dendritic carbons with hierarchical porosity: beyond the diffusion limitation

Abstract

The direct activation of oxygen molecules in the gas phase at the interface of solid (catalyst), liquid (electrolyte) and gas (oxygen gas) is highly alluring for the oxygen reduction reaction (ORR) catalyst in a liquid-phase reactor. Such a multiphase pathway without the limitation of the diffusion rate of the dissolved oxygen molecules promises a much higher catalytic efficiency. However, a stable gas–liquid–solid interface can hardly be maintained due to the high surface tension of the aqueous solution to repel the gas phase on the surface of conventional ORR electrodes. Taking advantage of graphene layers with super-absorbing nature, we designed a dendritic carbon structure catalyst to stabilize oxygen bubbles in the nano-intervoids of the dendrites without loss of conductivity and structural integrity, achieving the direct reduction of oxygen gas in an aqueous electrolyte and an ultra-high ORR current density without a diffusion controlled plateau.