The CO₂ Concentration Inversion Effect: *CO Generation Rate and *CO C–C Coupling Efficiency as Dual Kinetic Descriptors for Catalyst-Dependent C₂₊ Selectivity in Dilute CO₂ Electroreduction¹
- 1Institute for Energy Research
- 2Jiangsu University
Abstract
The electrochemical reduction of dilute CO₂ (5–33% v/v) to multicarbon (C₂₊) products offers a sustainable route to directly utilize industrial exhaust, bypassing energy-intensive CO₂ capture and purification. Our systematic investigations from 2023 to 2026 reveal a counter-intuitive paradigm: under dilute CO2 feed ranging (e.g. from 25% to pure CO2), the C2+ selectivity of copper-based catalysts not only matches but can surpass the pure CO2 baseline. Here, we define the CO₂ Concentration Inversion Effect: a kinetic regime where the FE(C₂₊)/FE(C₁) ratio under dilute CO₂ feed exceeds that under pure CO₂ at identical potentials. This non-monotonic selectivity demonstrates that C₂₊ formation is governed by a catalyst-tunable balance between *CO supply and coupling kinetics. Critically, we introduce two quantitative kinetic descriptors that jointly govern the fate of *CO intermediates: the *CO production rate (the total flux of *CO supplied to the surface) and the C-C coupling efficiency of *CO (the fraction of that *CO consumed by C-C coupling). While the definitions of these descriptors are general, their joint systematic quantification and mechanistic application as a dual-descriptor framework represent a significant advance. We demonstrate that C2+ selectivity is synergistically controlled by both the *CO generation rate and the *CO C-C coupling efficiency, both of which are modulated by applied potential and local reaction environments. In-situ FT-IR spectroscopy and systematic pH-dependent measurements reveal that the coupling efficiency is primarily governed by CO2 concentration rather than bulk pH, although the boundaries of the inversion window (Cmin, Cpeak, Cmax) shift with electrolyte conditions. Notably, we resolve a mechanistic decoupling between microscopic coupling efficiency and macroscopic FE(C2+)/FE(C1) ratios: while coupling efficiency reflects the intrinsic branching ratio of *CO intermediates, the macroscopic selectivity is optimized at an intermediate *CO supply where the absolute flux and suppression of competing C1 pathways dominate. This framework, validated across diverse catalyst families including B-doped Cu, Ag@Cu2O, and Cu(OH)2-derived Cu, establishes five key advances: (i) the explicit definition of coupling efficiency as a quantitative ratio, alongside *CO production rate; (ii) its absolute quantification across CO2 concentrations; (iii) cross-system validation of the dual-descriptor framework; (iv) the elucidation of the decoupling between efficiency and selectivity at high *CO coverage; and (v) their use as design criteria for catalyst optimization. This framework suggests that optimizing the *CO supply-coupling balance at dilute concentrations may offer distinct advantages for carbon upcycling compared to incremental improvements under pure feeds.
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BibTeX
@misc{yu2026co₂,
title = {{The CO₂ Concentration Inversion Effect: *CO Generation Rate and *CO C–C Coupling Efficiency as Dual Kinetic Descriptors for Catalyst-Dependent C₂₊ Selectivity in Dilute CO₂ Electroreduction¹}},
author = {Qing Yu and Ying Zhang and Peng Zhu and Qiankang Zhang},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15006687/v2},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15006687/v2},
note = {CC BY},
}
RIS
TY - UNPB
TI - The CO₂ Concentration Inversion Effect: *CO Generation Rate and *CO C–C Coupling Efficiency as Dual Kinetic Descriptors for Catalyst-Dependent C₂₊ Selectivity in Dilute CO₂ Electroreduction¹
AU - Qing Yu
AU - Ying Zhang
AU - Peng Zhu
AU - Qiankang Zhang
PY - 2026
DA - 2026/09/20
PB - ChemRxiv
DO - 10.26434/chemrxiv.15006687/v2
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15006687/v2
AB - The electrochemical reduction of dilute CO₂ (5–33% v/v) to multicarbon (C₂₊) products offers a sustainable route to directly utilize industrial exhaust, bypassing energy-intensive CO₂ capture and purification. Our systematic investigations from 2023 to 2026 reveal a counter-intuitive paradigm: under dilute CO2 feed ranging (e.g. from 25% to pure CO2), the C2+ selectivity of copper-based catalysts not only matches but can surpass the pure CO2 baseline. Here, we define the CO₂ Concentration Inversion Effect: a kinetic regime where the FE(C₂₊)/FE(C₁) ratio under dilute CO₂ feed exceeds that under pure CO₂ at identical potentials. This non-monotonic selectivity demonstrates that C₂₊ formation is governed by a catalyst-tunable balance between *CO supply and coupling kinetics. Critically, we introduce two quantitative kinetic descriptors that jointly govern the fate of *CO intermediates: the *CO production rate (the total flux of *CO supplied to the surface) and the C-C coupling efficiency of *CO (the fraction of that *CO consumed by C-C coupling). While the definitions of these descriptors are general, their joint systematic quantification and mechanistic application as a dual-descriptor framework represent a significant advance. We demonstrate that C2+ selectivity is synergistically controlled by both the *CO generation rate and the *CO C-C coupling efficiency, both of which are modulated by applied potential and local reaction environments. In-situ FT-IR spectroscopy and systematic pH-dependent measurements reveal that the coupling efficiency is primarily governed by CO2 concentration rather than bulk pH, although the boundaries of the inversion window (Cmin, Cpeak, Cmax) shift with electrolyte conditions. Notably, we resolve a mechanistic decoupling between microscopic coupling efficiency and macroscopic FE(C2+)/FE(C1) ratios: while coupling efficiency reflects the intrinsic branching ratio of *CO intermediates, the macroscopic selectivity is optimized at an intermediate *CO supply where the absolute flux and suppression of competing C1 pathways dominate. This framework, validated across diverse catalyst families including B-doped Cu, Ag@Cu2O, and Cu(OH)2-derived Cu, establishes five key advances: (i) the explicit definition of coupling efficiency as a quantitative ratio, alongside *CO production rate; (ii) its absolute quantification across CO2 concentrations; (iii) cross-system validation of the dual-descriptor framework; (iv) the elucidation of the decoupling between efficiency and selectivity at high *CO coverage; and (v) their use as design criteria for catalyst optimization. This framework suggests that optimizing the *CO supply-coupling balance at dilute concentrations may offer distinct advantages for carbon upcycling compared to incremental improvements under pure feeds.
ER -