Defective Carbon Catalysts with Graphitic N-Modified Adjacent Pentagons as Active Sites for Boosted Oxygen Reduction Reaction in Seawater

Seawater electrocatalysis is highly desired for various energy storage and conversion systems, such as water splitting using seawater as an electrolyte and metal fuel cells. However, the adsorption of chloride ions (Cl^-) on the active sites of cathodes would worsen the oxygen reduction reaction (ORR) activity and stability, thus lowering the battery performance. Herein, the coupling active sites of graphitic N-regulated adjacent pentagon defects in carbon nanosheets (GAP/CN) were first synthesized by a low-boiling-point metal-mediated partial N-removal strategy. Experimental and theoretical results affirm the advantageous cooperative effect between adjacent pentagons and graphitic N toward the ORR in a harsh seawater environment, where adjacent pentagons act as the authentic highly effective ORR active sites and surrounding graphitic N site serves as the structural regulator to weaken the binding strength of harmful Cl^- to prevent catalyst poisoning. As a result, GAP/CN delivers excellent ORR activities in diverse electrolytes, including 0.1 M KOH (half-wave potential of 0.87 V), alkaline artificial seawater (half-wave potential of 0.87 V), and natural seawater (half-wave potential of 0.71 V), and also good long-term stability, which can be comparable to commercial Pt/C. This study provides valuable guidance for the rational design of ORR electrocatalysts for seawater-related energy-conversion devices.