Graphitization Degree Regulation of Carbon‐Coated Catalysts to Improve the Freshwater/Seawater Splitting Performance

Abstract Advancing efficient oxygen evolution reaction (OER) catalysts for both freshwater and seawater electrolysis to enable sustainable green hydrogen production is a critical yet challenging pursuit in renewable energy research. In this work, a N‐doped carbon nanotube encased NiFe alloy catalyst (NiFe@NCNT) is designed and synthesized, to balance the trade‐off effect of the activity and stability with optimizing the graphitization degree of the carbon shell. The NiFe@NCNT catalyst demonstrates exceptional OER performance in both freshwater and seawater electrolytes, owing to its high conductivity, abundant active sites, robust anticorrosion properties. The NiFe@NCNT exhibits the overpotentials as low as 270 mV in 1 M KOH and 303 mV in 1 M KOH + seawater to reach 10 mA cm −2 , coupled with robust stability under operational conditions. Remarkably, the Pt/C||NiFe@NCNT pair demonstrates superior performance, attaining 10 mA cm −2 at 1.627 V in 1 M KOH + seawater electrolyte, outperforming the conventional Pt/C||RuO 2 configuration and highlighting its immense potential for scalable green hydrogen production from seawater.