Introducing Lewis Base‐Phosphate to Boost Neutral Seawater Splitting in Anion Exchange Membrane Electrolyzer
Mei Han, Haibin Wang, Jieshu Zhou, Kangning Liu, Ning Wang, Xihao Chen, Yongchang Liu, Hongyan Liang
Abstract
Abstract Electrolysis of seawater using anion exchange membrane water electrolyzers (AEMWEs) under neutral conditions, is an attractive method for hydrogen production. Unfortunately, competitive anodic chlorine evolution reaction together with sluggish oxygen evolution reaction (OER) kinetics caused by insufficient OH − , significantly limit the system's current density and operational stability. Herein, Lewis base phosphate (PO 4 3− ) is used as a proton acceptor to accelerate the cleavage of OH−H bonds, which facilitates the accumulation of *OH. NiFeP nanosheets grown on pretreated nickel foam (NiS‐A) are used as the free‐standing electrode. During the OER process, the pre‐catalyst NiFeP spontaneously transforms into Lewis base‐PO 4 3− decorated Ni(Fe)OOH. Experimental studies and density functional theory calculations reveal that Ni(Fe)OOH active phases adsorb H 2 O intermediates and synergize with the protophilic Lewis base PO 4 3− to favor the dissociation of water molecules (*H 2 O→*OH+H + +e − ), ensuring the timely supply of *OH in neutral media. Meanwhile, PO 4 3− also exhibits excellent ability to repel chloride ions in seawater splitting, achieving ≈98.2% oxygen Faradaic efficiency. The optimized NiFeP/NiS‐A delivers a low overpotential (280 mV at 10 mA cm −2 ) and long‐term OER durability (over 400 h at 500 mA cm −2 ). Integrating NiFeP/NiS‐A in a seawater‐based AEMWE can achieve an industrially required current density of 1.0 A cm −2 (60 °C) at 1.8 V and an operation stability over 220 h.