Abstract
<jats:p>Reducing CO2 partial pressure in electrocatalytic CO2 reduction (CO2RR) to multicarbon (C2+) products has traditionally been considered detrimental due to mass transfer limitations and competitive hydrogen evolution. However, our systematic investigations from 2023 to 2026 reveal a counter-intuitive paradigm: under dilute CO2 feed ranging from 25% to pure CO2, with peak intensity at 25–50%, the C2+ selectivity of copper-based catalysts not only matches but can surpass the pure CO2 baseline. We define this phenomenon as the CO2 Concentration Inversion Effect, characterized by two inseparable features: (1) a concentration inversion where C2+ Faradaic efficiency under dilute CO2 (25% to pure CO2) exceeds the pure CO2 baseline for a given catalyst, with maximum enhancement typically observed at 25–50% CO2; and (2) a compositional inversion where catalysts optimal for pure CO2 (e.g., Cu2O-rich Ag@(Cu2O)3.0) drastically underperform in dilute CO2, while Ag-rich Ag@(Cu2O)0.75 becomes the optimal candidate. Quantitative mechanistic studies demonstrate that the rate-determining step (RDS) shifts from C–C coupling (pure CO2 regime) to *CO supply (dilute CO2 regime), with the *CO C–C coupling efficiency reaching up to 79.3% under 25% CO2. We further establish a design rule for dilute CO2 electrocatalysis: balancing *CO generation capacity with C–C coupling site availability, distinct from the optimization logic for pure CO2 systems. This concept redefines catalyst design for direct conversion of industrial flue gas to high-value C2+ products. The full boundary conditions of this effect remain an active area of investigation. Confined to copper-based catalysts capable of C–C coupling, we propose that it operates within a kinetic window governed by the balance between *CO generation and C–C coupling capacity. While effective from ~25% CO2 up to pure CO2, the precise concentration boundaries are intrinsically linked to the specific catalyst compositionpreliminary unpublished results from our laboratory on CuTCPP-derived Cu catalysts indicate that the optimal inversion concentration can extend to ~75% CO2, further corroborating the catalyst-tunable nature of the kinetic window.</jats:p>