N2-Plasma-Induced CN-Vacancies in NiCoFe PBAs Enhance Selective Oxygen Evolution Electrocatalytic Performance in Alkaline Seawater

Abstract

Cheap and advanced electrocatalysts for the oxygen evolution reaction (OER) are vitally significant but challenging for seawater electrolysis. Herein, a glow discharge N₂ plasma is used to etch the [Fe(CN)₆]^4– group of the NiCoFe Prussian blue analogue (PBA) framework by highly reactive nitrogen radicals (the catalyst named N₂-NiCoFe-PBA). Abundant CN vacancies (V_CN) generated by this etching effectively suppress the Fe loss from N₂-NiCoFe-PBA, while the lack of V_CN results in the Fe leaching from the NiCoFe-PBA precursor during the anodic process. Consequently, N₂-NiCoFe-PBA and NiCoFe-PBA are transformed into real active phases of NiCoFeOOH and NiCoOOH during the OER process, respectively. Theoretical calculations display that NiCoFeOOH has superior adsorption capacity toward OH^– over Cl^– to NiCoOOH, which is beneficial to excellent OER activity and anticorrosion performance in alkaline seawaters. In alkaline simulated and natural seawater, N₂-NiCoFe-PBA exhibits much better OER performance with smaller η₁₀₀ (293 and 323 mV) than NiCoFe-PBA (405 and 434 mV). N₂-NiCoFe-PBA can run stably over 110 h in an alkaline high-salty electrolyte (1 M KOH + 2.0 M NaCl) at 250 mA cm^–2. This study provides a modification method without destroying the structure to develop efficient and stable OER catalysts for seawater electrolysis.