Organic Ion-Mediated Electrostatic Shielding Facilitates Membrane-Free Electrochemical Hydrogen Production Coupling...

Electrolytic water splitting is a cornerstone technology for sustainable hydrogen (H₂) production. However, conventional methods face substantial challenges due to the slow kinetics of the oxygen evolution reaction (OER) and limitations imposed by ion-exchange membranes, highlighting the need for innovative approaches. This study introduces a novel, membrane-free electrolysis system that synergistically combines hydrogen generation with the recycling of spent lithium iron phosphate (LFP) batteries. Central to this system is the redox cycling of 2,2,6,6-tetramethylpiperidin-1-oxyl (4-HO-TEMPO), which facilitates electron transfer from LFP. To mitigate parasitic reactions in the absence of a membrane, an electrostatic shielding mechanism is implemented through the addition of polyquaternium-7 (PQ-7) to the electrolyte. This strategy effectively suppresses the unwanted reduction of redox-active species by electrostatically repelling them from the electrode surface, as evidenced by rotating disk electrode and electrochemical impedance spectroscopy analyses. The proposed system achieves a remarkable hydrogen faradic efficiency of 92.4% and facilitates lithium ion recycling at a rate of 54.45 mmol L^{- 1} h^{- 1} under a current density of 100 mA cm^{- 2}. Our work presents a straightforward yet effective strategy for membrane-free water electrolysis integrated with the sustainable recycling of spent LFP batteries through interfacial microenvironment control.