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

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.