Anion-Activated Supramolecular Proton Relays Enable Neutral-pH and Seawater Oxidation

Abstract

Neutral-pH and direct seawater oxidation are critically hindered by sluggish proton-coupled electron transfer (PCET) and competitive chloride corrosion. Here, we employ surface-confined azacrown macrocycles of varying nitrogen content as supramolecular proton-management layers rather than conventional redox catalysts. In neutral phosphate buffer, OER activity follows an unconventional one aza > two aza ≫ six aza macrocycle trend, with Cu/Hexaaza exhibiting purely capacitive behavior that switches to superior catalysis at 4 °C. Combined Gerischer impedance and DFT analyses reveal an anion-assisted PCET mechanism wherein phosphate binding narrows the HOMO–LUMO gap, transforming electronically inert hosts into a highly polarizable proton–anion assembly. The computational studies show that the interfacial activity is governed not by maximal proton affinity, but by an optimal enthalpy–entropy balance between proton storage and Grotthuss-type hopping. While hexaaza (HAZ) overstabilizes protons at ambient temperature, monoaza (MAZ) enables rapid, exchange-dominated proton shuttling. Substituting Cu foam with a graphite sheet delivers a metal-free OER in intact seawater without pH adjustment or desalination.