Designing reliable and accurate isotope-tracer experiments for CO2 photoreduction

Abstract

The photoreduction of carbon dioxide (CO2) into renewable synthetic fuels is an attractive approach for generating alternative energy feedstocks that may compete with and eventually displace fossil fuels. However, it is challenging to accurately trace the products of CO2 photoreduction on account of the poor conversion efficiency of these reactions and the imperceptible introduced carbon contamination. Isotope-tracing experiments have been used to solve this problem, but they frequently yield false-positive results because of improper experimental execution and, in some cases, insufficient rigor. Thus, it is imperative that accurate and effective strategies for evaluating various potential products of CO2 photoreduction are developed for the field. Herein, we experimentally demonstrate that the contemporary approach toward isotope-tracing experiments in CO2 photoreduction is not necessarily rigorous. Several examples of where pitfalls and misunderstandings arise, consequently making isotope product traceability difficult, are demonstrated. Further, we develop and describe standard guidelines for isotope-tracing experiments in CO2 photoreduction reactions and then verify the procedure using some reported photoreduction systems.

Boosting Artificial Photosynthesis: CO2 Chemisorption and S-Scheme Charge Separation via Anchoring Inorganic QDs on COFs

“…The corresponding mass spectra display prominent peaks at m/z = 29 and m/z = 17, corresponding to 13 CO and 13 CH 4 , respectively (Figure 5e,f). 68 Together with the observed fragments generated from the two peaks, this unequivocally confirms that the reduction products CO and CH 4 indeed stem from CO 2 molecules.…”

Recent Advances on the Utilization of TiO2‐Based Catalysts in the Photocatalytic Reduction of CO2 to Methane

“…Additional TiO 2 photocatalyst modifications, such as heterojunction and vacancy introduction can further enhance CH 4 selectivity. Furthermore, verifying CO 2 photocatalytic reduction products can be accomplished by the 13 C isotope‐tracing approach [120] which substitutes 13 CO 2 for CO 2 as a gas feed. Various instruments, including nuclear magnetic resonance spectroscopy (NMR), [121] fourier transforms infrared spectroscopy (FT‐IR), [120] and gas chromatography‐mass spectrometry (GC‐MS) [67] can be employed for 13 C isotope‐tracing.…”

“…Furthermore, verifying CO 2 photocatalytic reduction products can be accomplished by the 13 C isotope‐tracing approach [120] which substitutes 13 CO 2 for CO 2 as a gas feed. Various instruments, including nuclear magnetic resonance spectroscopy (NMR), [121] fourier transforms infrared spectroscopy (FT‐IR), [120] and gas chromatography‐mass spectrometry (GC‐MS) [67] can be employed for 13 C isotope‐tracing. Among these, GC‐MS is the widely used and reliable choice for tracking isotopes in CO 2 photoreduction [122] .…”

“…Among these, GC‐MS is the widely used and reliable choice for tracking isotopes in CO 2 photoreduction [122] . GC‐MS separates molecular species on the column based on affinity and measures mass‐to‐charge ratio ( m/z ) to distinguish isotope abundance [120,122] as shown in Figure 29. Notably, the major peaks for 13 CO 2 , 13 CH 4 , and 13 CO appear at m/z =45, m/z =17, and m/z =29, respectively.…”

Highly Selective Photoconversion of CO2 to CH4 over SnO2/Cs3Bi2Br9 Heterojunctions Assisted by S-Scheme Charge Separation

“…The dominant and fragmental peaks in their corresponding mass spectra are highly consistent with the standard spectra of CH 4 and CO from the National Institute of Standards and Technology (NIST) library (Figure S20), confirming that the products indeed derive from 13 CO 2 (Figures 5e, S21, and S22). 62 The recyclability of the SnO 2 / Cs 3 Bi 2 Br 9 heterojunction (SC4) for CO 2 photoreduction reveals that the decay in the production yield of all products decreases moderately after four cycles (Figure S23). The XRD pattern (Figure S24) and XPS spectra (Figure S25) of the spent SC4 after photoreactions show inconspicuous changes in comparison with the fresh ones, indicating excellent photostability of the SnO 2 /Cs 3 Bi 2 Br 9 nanohybrids.…”