Ionic Liquid Cations-Mediated Biomimetic Proton Relays on Metal Nanoclusters for Selective Two-Electron Oxygen Reduction

Comprehensive Summary Electrocatalytic two-electron oxygen reduction reaction (2 e – ORR) represents a green and sustainable way for H 2 O 2 production, while its practical applications in industry are largely hindered by the unwieldy proton transfer kinetics. Herein, we develop a biomimetic interface engineering strategy to precisely regulate proton transfer kinetics for enhanced 2 e – ORR. Using atomically precise Au 25 ( p -MBA) 18 nanoclusters (NCs, p -MBA = 4-mercaptobenzoic acid) as model catalysts, we introduced a series of quaternary ammonium ionic liquid (IL) cations onto the cluster surface via combined electrostatic and π-π stacking interactions. The hydrophobic tails and controlled hydrolysis of IL cations disruptthe long-range interconnected hydrogen-bonding networks, which are ubiquitous in alkaline electrolytes and bring about an overwhelming proton transfer rate. Instead, a mild biomimetic proton relay mechanism favoring 2 e – ORR can be established and fine-adjusted, leveraging deprotonation and protonation equilibrium of IL cations. By this way, the optimized system can bring down the mean electron transfer number ( n ) to 2.45 and promote the H 2 O 2 selectivity to 90% or higher, evidencing a pronounced shift toward the 2 e – ORR pathway under alkaline conditions. This work underscores the usefulness of atomically precise interfacial engineering in optimizing the electrocatalytic performance of inorganic nanocatalysts.