Collision-programmed Selectivity in CO₂ Electrochemical Reduction via Co-engineering Electron Transfer Duty Cycle and...

Selectivity of electrochemical CO₂ reduction reaction (ECO₂RR) is typically pursued by optimizing immobilized catalyst films biased at constant potential, an approach referred to as "catalyst-fixed electrochemistry". This architecture hinges on two variables that are difficult to tune: the electron-transfer (ET) environment and local mass transport. Here we introduce a fundamentally different concept: a "catalyst-fluidized electrochemistry" platform, where freely suspended catalyst particles make stochastic, short-lived contacts with the electrode. This dynamic system co-engineers the ET duty cycle (intermittent vs. continuous) and the local proton supply (spherical/fast vs. planar/slow transport), transforming two traditional constraints into tunable operating parameters. Co-modulating these levers and, when desired varying them independently, improves the selectivity of high-value products and reveals how each steers pathway branching. Using AuCu₂ nanoparticles as a model catalyst, fluidization boosts 9.2-fold and 2.5-fold enhancement in Faradaic efficiency (FE) for ethylene (C₂H₄) and formic acid (HCOOH) under high and low overpotentials, respectively, relative to the corresponding fixed-film configuration. Pulsed-potential emulation isolates ET intermittency, while experiments together with DFT-informed microkinetic modeling indicate that increased surface proton availability further biases the reaction toward C₂ formation at high overpotentials. Reaction environment programming thus emerges as a catalyst-agnostic lever for reconfiguring reaction networks, complementing conventional materials design.