Universal Kinetic Mechanism Describing CO₂ Photoreductive Yield and Selectivity for Semiconducting Nanoparticle Photocatalysts

Abstract

Photocatalytic conversion of CO 2 to generate high-value and renewable chemical fuels and feedstock presents a sustainable and renewable alternative to fossil fuels and petrochemicals. Currently, there is a dearth of kinetic understanding to inform better catalyst design, especially at uniform reaction conditions across diverse catalytic species. In this work, we investigate 12 active, stable, and unique but common nanoparticle photocatalysts for CO 2 reduction at room temperature and low partial pressure in aqueous phase: TiO 2 , SnO 2 , and SiC deposited with silver, gold, and platinum. Our analysis reveals a single consistent chemical kinetic mechanism, which accurately describes the yield and selectivity of all single-carbon containing (C1) products obtained in spite of the diverse catalysts employed. Formaldehyde is predicted as the first product in the reaction network and we report, to the best of our knowledge, the highest selectivity to date toward formaldehyde during CO 2 photoreduction when compared against all other C1 products (∼80%) albeit at low CO 2 conversion (<0.5 μmol g cat −1 h −1 , <16.8 nmol m −2 h −1 ). Further, we observe a volcano-like relationship between the electron-transfer rate of a given photocatalyst for CO 2 reduction and the net rate at which reduced products are produced in the reaction mixture taking into account unfavorable product oxidation. We establish an empirical upper limit for the maximum rate of production of CO 2 reduction products for any nanoparticle photocatalyst in the absence of a hole-scavenging agent. These results form the basis for the design and optimization of the next generation of highly efficiency and active photocatalysts for CO 2 reduction.

Intermediates and their conversion into highly selective multicarbons in photo/electrocatalytic CO2 reduction reactions

“…27). 132 To elucidate the role of the kinetics of elementary steps on Cu electrodes for CO 2 electroreduction, Janik and Asthagiri 71 presented a DFT study that considered the rate of electron-ion transfer reactions and provided an alternative reaction path that explained both the methane and ethylene production through a hydroxymethylidyne (COH) intermediate from CO reduction, which was consistent with experimental ndings. The study showed that considering solely the thermodynamics of reaction free energies was misleading for methane production, and the reaction kinetics of elementary steps were much more favorable for producing results consistent with the experimental data.…”

Controllable CO2 Reduction or Hydrocarbon Oxidation Driven by Entire Solar via Silver Quantum Dots Direct Photocatalysis

“…This characteristic supported that Ag-QDs were the active center of photoreduction. [25,48] Small 2023, 19, 2207234 According to the results of photooxidation and photoreduction experiments, it was believed that Ag-QDs should directly act as the reaction center in the SMSI metal/semiconductor system rather than just improved the semiconductor charge separation efficiency. Therefore, in situ P-TPD tests were designed to further confirm this hypothesis.…”

Revealing the stochastic kinetics evolution of photocatalytic CO2reduction

“…The photocatalytic solid-liquid reaction is usually carried out in the reactor equipped with a magnetic stirrer, and the motion of photocatalysts in suspensions results in a nonstable process of light absorption for each nanoparticle. [8][9][10] Incident photons are absorbed in variable positions within photocatalysts, which leads to the random generation of charge carriers. It is different from the generation of charge carriers in solar cells or photo-electro catalysis.…”