Designing reliable and accurate isotope-tracer experiments for CO2 photoreduction

Wang, Shengyao; Jiang, Bo; Henzie, Joel; Xu, Feiyan; Liu, Chengyuan; Meng, Xianguang; Zou, Sirong; Song, Hui; Pan, Yang; Li, Hexing; Yu, Jiaguo; Chen, Hao; Ye, Jinhua

doi:10.1038/s41467-023-38052-0

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Published: 03 May 2023

Designing reliable and accurate isotope-tracer experiments for CO₂ photoreduction

Nature Communications volume 14, Article number: 2534 (2023) Cite this article

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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.

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Introduction

If sunlight can be efficiently harnessed as a primary energy source for the photoreduction of CO₂ into synthetic fuels, it will contribute a large flow of carbon-neutral energy in a material format that is compatible with existing fossil fuel infrastructure^{1,2,3,4,5,6,7,8}. At a large enough scale, this technology may enable the control of atmospheric CO₂ levels and make fossil fuels obsolete in the coming decades^9,10,11,12. However, considerable scientific and technical challenges must be overcome to realize CO₂ photoreduction reactions with high selectivity and conversion efficiency^{13,14,15,16,17,18}. After many decades of exploration, most experimental studies focus on optimizing materials and reaction systems^{19,20,21,22,23,24}. Most reported CO₂ photoreduction systems are not yet able to deliver the desired products on a practical scale and with long-term operational stability. The low selectivity and CO₂ conversion efficiency of most existing reaction systems²⁵ is a significant roadblock in this field because it is challenging to attribute potential products (e.g., CO, alkanes, alcohols, carboxylic acids, and alkenes) solely to CO₂ photoreduction processes^26,27. Unfortunately, the efficiency of some high-performance reaction systems is later attributed to the decomposition of the carbon contaminants on the photocatalyst or the reaction system^{28,29,30,31,32}.

Increasing awareness of the challenge of attributing products to CO₂ photoreduction has made ¹³C isotope labeling experiments essential^33,34,35. Lehn et al. carried out isotope labeling experiments with ¹³CO₂ in 1983, revealing that the reduction product of CO indeed came from CO₂ by using gas chromatography-mass spectrometry (GC-MS). However, no standard test method was mentioned in this research^36,37. Later, Willner et al. used ¹³C nuclear magnetic resonance spectroscopy (NMR) to show that H¹³COO⁻ originates from H¹³CO₃⁻ (the dissolved ¹³CO₂ in solution)³⁸. Over the years, various techniques using NMR spectroscopy and Fourier transform infrared spectroscopy (FT-IR) have been employed in isotope-tracer studies: the approach of ¹H-NMR is efficient for liquid product analysis through peak shifts and coupling constants of the ¹³C-linked hydrogen; FT-IR equipped with a gas cell is effective for gaseous product analysis via the increased path length of a beam by multiple internal reflections^39,40. Still, both methods are relatively insensitive to various carbon isotopes. Thus GC-MS-based techniques are still the most reliable and universal strategy for isotope-tracer studies in CO₂ photoreduction^41,42. For example, numerous organic carbon-containing photocatalysts, such as conjugated polymers, Metal-organic frameworks (MOFs), and Covalent organic framework (COFs), have good activities in CO₂ photoreduction^{43,44,45,46,47,48}. Isotope-tracing studies with GC-MS allow researchers to exclude carbon contamination from the decomposition of these catalysts or the materials synthesis process. Current isotope-tracer methods can measure simple samples such as ¹³CO, H¹³COOH, ¹³CH₄, ¹³C₂H₆, ¹³C₂H₄, and ¹³CH₃OH due to the isotope effects induced by different mass-to-charge ratios^49,50,51,52. However, once the abovementioned series of molecular substances are generated during CO₂ photoreduction, the inherent ionization process of mass detection could not only charge the molecules but also inevitably cause chemical bonds to break in these molecules, making the isotope-tracing via mass detection becomes increasingly difficult as molecular fragments with similar m/z ratios interfere and lead to misidentification and errors in quantification. Even for the emerging synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) strategy, the existence of interfering factors induced by the long-time sampling is also uncertain⁵³. So the gas chromatograph (GC) is essential to be added to the sampling system to separate molecular species before collecting mass spectra (MS)^54,55.

Despite the fact that isotope-tracer experiments are regarded as solid corroborating evidence for CO₂ photoreduction, the current protocols are still substandard, causing the literature to be rife with false-positive results⁵⁶. Meanwhile, the accurate and effective solution of isotope detection for various products in CO₂ photoreduction is still lacking, which causes the community to be suspicious of all results. In the present work, we confirmed the pros and cons of the current mass spectrometry protocol as well as the emerging technology of synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) when they applied to the isotope-tracer experiments in CO₂ photoreduction. We also experimentally performed isotope-tracer experiments on various isotope standards and described a standard protocol assessing various potential products of CO₂ reduction. In addition, some classic CO₂ photoreduction systems reported in the literature were also used to validate our protocols. It is imperative to settle on an appropriate scientific method for isotope-tracer studies to promote trust in the community as we develop and benchmark some materials systems for CO₂ photoreduction. This research illustrates the pitfalls and misunderstandings in isotope-tracer studies and also provides examples and references for ¹³C isotope-tracer methods so we can all obtain solid evidence that reduction products are firmly attributed to CO₂ photoreduction reactions.

Results

Importance of separation for multicomponent samples

GC-MS is the most common instrument for tracing isotopes in CO₂ reduction reactions currently. The GC-MS instrument is composed of a GC to separate molecular species based on affinity with a column material and an MS to detect their mass or their mass fragments (Fig. 1a). However, the current method for tracing isotopes in CO₂ reduction reactions ignores this. We verified the reliability of the current method. To mimic the products and conditions of a real photoreduction reaction, we directly employed standard gases such as ¹³CO₂, ¹³CO, and vapor in the CO₂ reduction system. The volume ratio of ¹³CO >5% v/v is much higher than the yield of CO in the usual CO₂ photoreduction process. Then these premixed gases were collected from the CO₂ reduction system and injected into the GC-MS equipped with a commercial HP-5ms column (see “Methods” for experimental details). As shown in Fig. 1b, a peak at m/z = 29 in the mass spectrogram could be obtained from TIC at an RT of 6.4 min. This peak has a definite value, but it could originate from three sources: (i) it is a molecular ion of ¹³CO (¹³CO⁺, m/z = 29), (ii) a fragment ion of ¹³CO₂ (¹³CO⁺, m/z = 29), or (iii) it is a molecular ion of ¹⁵N¹⁴N (the natural abundance of nitrogen isotope, ¹⁵N¹⁴N⁺, m/z = 29). This could be further confirmed via the GC-MS analysis of pure ¹³CO₂, ¹³CO, and N₂ (Supplementary Figs. 1–3). Although the natural abundance of the nitrogen isotope exists in traces, the ¹³CO₂ fragment ion is abundant and has the same characteristics to interfere with the isotope-tracer results for ¹³CO. Consequently, even if there is no ¹³CO in the injected mixture (only ¹³CO₂ and vapor were injected into GC-MS), a similar mass spectrogram can be obtained under the same conditions (Fig. 1c), generating a peak at m/z = 29. This peak could be mainly attributed to the fragment ion (¹³CO⁺) generated from the dissociation of ¹³CO₂. Even the deactivated fused silica tube (the length is 5 m), without any separation effect, acts as the connector to let all components (¹³CO₂ and vapor) enter the quadrupole together; a similar result can also be obtained in the mixture of ¹³CO₂ and vapor even without a photocatalytic reduction process (Supplementary Fig. 4). Moreover, the selected m/z = 45, 29 and 17 can be detected (Supplementary Fig. 5) when the detection method of GC-MS is set to the selected ion monitoring (SIM) mode (see “Methods” for experimental details). It is always used as evidence of traceability for the products originating from CO₂ photoreduction, and signals at m/z = 17, 29, and 45 are assigned to CH₄, CO, and CO₂ molecular ions, respectively⁵⁷. However, based on the above analysis, the presence of dissociated ¹³CO₂ (generated fragments of ¹³CO⁺, m/z = 29) and vapor (generated fragments of HO⁺, m/z = 17) throws these conclusions of traceability into doubt.

**Fig. 1: The contemporary approach toward isotope-tracing experiments in CO₂ photoreduction.**

For such confusing results, we could ascribe them to the detection principle of MS detector for charged species. Namely, the process of charging molecules in an MS detector is not so controllable, and there is some probability that the dissociation of the molecules coincides with ionization. In particular, when the amount of the sample is large, the probabilistic dissociation and dissociative recombination become inevitable, causing molecular ions and fragmented ions with the same characteristics to interfere with each other on the MS detector⁵⁷. As a result, confusion could occur in the isotope detection for the product of ¹³CO due to the simultaneous process of ionization and dissociation over the ¹³CO₂ and H₂O reactants, ¹³CO product, and air components (N₂, O₂, Ar), respectively (Fig. 2a).

**Fig. 2: The pitfalls and misunderstandings arise in the contemporary approach.**

To avoid this confusion, suitable chromatographic conditions are a prerequisite to meeting the requirement of sample separation. As shown in Fig. 2b, a GC separator equipped with a suitable chromatographic column can separate mixed gases of CO₂ and CO so that they are ideally queued in a single file before entering the MS detector. Thus although both CO₂ and CO can generate the same fragment ions in the ion source, their different entry times provide resolution. As a result, two signal peaks appeared at different retention times (RT) in the total ion chromatography (TIC). Their corresponding mass spectrogram (MS₁ and MS₂ selected at different RT) show both molecular ions and fragment ions, which can be clearly attributed to either CO or CO₂. In contrast, chromatography columns with bad separation characteristics allow components of CO₂ and CO to enter the ion source simultaneously and generate complex molecular ions and fragment ions. These then enter the quadrupole together, resulting in a single peak on TIC and a corresponding mass spectrogram (MS). This spectrogram is very close to the abovementioned MS₁ obtained from the fully separated samples. However, the signal corresponding to CO⁺ could be attributed to a fragment ion of CO₂ or a molecular ion of CO, making it impossible to distinguish the source of CO⁺. Similarly, it is impossible to attribute the signal from C⁺ or O⁺ because both CO₂ and CO can generate it.

Apart from the abovementioned method of mass spectrometry for isotope traceability, recently, an emerging technique called the synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was also used to assign CO products to CO₂ photoreduction reactions⁵⁸. This analytical technique is useful because it delivers high-intensity, high-resolution, and widely tunable photon energies for photoionization processes. SVUV-PIMS enables selective and sensitive ionization (see “Methods” for experimental details) and can overcome the drawbacks of other ionization techniques and minimize fragmentation interference in MS detection. As shown in Fig. 3a, the m/z = 45 signal gives an ionization threshold of 13.75 eV in the photoionization spectra of pure ¹³CO₂, while pure ¹³CO exhibits an increased ionization threshold of 14.00 eV in the m/z = 29 signal and the response rate of CO 10 times less than that of CO₂. However, the SVUV-PIMS signal at m/z = 29 is also observed at 13.91 eV for pure ¹³CO₂ (Fig. 3b). This feature matches the weak fragmentation of ¹³CO₂ or via impurities introduced during the production of ¹³CO₂ gas, interfering with the detection of ¹³CO to some extent. Therefore, when the photon energy of SVUV-PIMS was set at 14.50 eV to monitor the isotope product of ¹³CO, the peak at m/z = 29 can be found in the SVUV-PIMS spectra of pure ¹³CO₂ (Fig. 3c) that is similar to the spectra obtained from the mixture of ¹³CO and ¹³CO₂ (inset of Fig. 3c). Moreover, the intensity of m/z = 45 signal in pure ¹³CO₂ is strongly associated with the increased repulsion voltage and sampling time (Fig. 3d). Although SVUV-PIMS minimizes fragmentation of the potential analytes, the popularity of this technique and the excessive demand of sample (hundred milliliters) hamper the extensive application of SVUV-PIMS to some extent. Moreover, the existence of interfering factors in this strategy induced by the long-time sampling is just like the SIM model in GC-MS, which cannot be ignored in the isotope-tracer experiment for CO₂ photoreduction. Therefore, a complete separation of multiple components in GC is essential to obtain reliable isotope-tracing results for the products of CO₂ photoreduction in MS.

**Fig. 3: SVUV-PIMS for isotope-tracing experiments in CO₂ photoreduction.**

Analysis strategy for the isotope-labeled products of CO₂ photoreduction

Potential products of CO₂ photoreduction reactions include CO, CH₄, C₂H₆, C₂H₄, HCOOH, CH₃COOH, CH₃OH, and CH₃CH₂OH. Isotope-tracing experiments are complicated because products are inevitably mixed with the reactants (H₂O and CO₂) and impurities introduced during sampling (e.g., N₂ and O₂ via the airtight syringe). In addition, chromatographic columns such as HP-5ms in GC-MS cannot separate these gas components in isotope-tracing experiments. Thus, selecting a suitable column for separating permanent gas components is critical. For example, the HP-Molesieve column (see “Methods” for experimental details), as shown in Fig. 4a, can completely separate O₂ (RT at 3.65 min), N₂ (RT at 4.37 min), CH₄ (RT at 5.25 min), and CO (RT at 7.25 min). After complete separation, it prevents the introduced air components during the injection process from interfering with the detection of products. The obtained mass spectra of O₂ and N₂ closely match the NIST mass spectral library (Supplementary Figs. 6 and 7), and the m/z of carbon-related molecular ions and fragment ions generated from ¹³CH₄ (¹³CH₄⁺, m/z = 17; ¹³CH₃⁺, m/z = 16; ¹³CH₂⁺, m/z = 15; ¹³CH⁺, m/z = 14; and ¹³C⁺, m/z = 13) and ¹³CO (¹³CO, m/z = 29 and ¹³C, m/z = 13) have a mass shift effect (M+1) compared with the non-isotope-labeled CH₄ (Supplementary Fig. 8) and CO (Supplementary Fig. 9), respectively. Nevertheless, the molecular sieve column will irreversibly adsorb the reactant of CO₂; thus, MS analysis of the reactant (CO₂) and the products (CO or CH₄) cannot be obtained simultaneously with the HP-Molesieve. To confirm the isotopic abundance of CO₂, the HP-PLOT/Q is employed (see “Methods” for experimental details). As shown in Fig. 4b, the CH₄ (RT at 4.87 min) and CO₂ (RT at 6.60 min) elute as separate peaks in the TIC, and the corresponding MS of ¹³CH₄ and ¹³CO₂ (¹³CO₂⁺, m/z = 45; ¹³CO⁺, m/z = 29; and ¹³C⁺, m/z = 13) could be obtained, respectively. The peaks exhibit a mass shift effect (M+1) compared to the non-isotope-labeled standards of CH₄ (Supplementary Fig. 8) and CO₂ (Supplementary Fig. 10). However, the air-derived components (e.g., O₂ and N₂) and CO (RT at 3.83 min) cannot be separated well under these conditions and may interfere with the analysis of CO isotopes. Interestingly, two kinds of C₂ hydrocarbons (C₂H₆, RT at 8.21 min and C₂H₄, RT at 6.60 min) could be distinguished under these conditions. Although both ¹³C₂H₄ and ¹³C₂H₆ exhibit the same highest peak at m/z = 30, ¹³C₂H₆ possesses two more characteristic peaks at m/z = 31 and m/z = 32 that can only be generated from the fragment ion of ¹³C₂H₅⁺ and molecular ion of ¹³C₂H₆⁺. The ratio between the peaks that recorded in MS of ¹³C₂H₄ (¹³C₂H₄⁺, m/z = 30; ¹³C₂H₃⁺, m/z = 29; ¹³C₂H₂⁺, m/z = 28; ¹³C₂H⁺, m/z = 27; and ¹³C₂⁺ m/z = 26) and ¹³C₂H₆ (¹³C₂H₆⁺, m/z = 32; ¹³C₂H₅⁺, m/z = 31; ¹³C₂H₄⁺, m/z = 30; ¹³C₂H₃⁺, m/z = 29; ¹³C₂H₂⁺, m/z = 28; ¹³C₂H⁺, m/z = 27; and ¹³C₂⁺, m/z = 26) is different. It is still consistent with the ratio of the non-isotope-labeled standards C₂H₄ (Supplementary Fig. 11) and C₂H₆ (Supplementary Fig. 12), respectively, which comply with the mass shift effect (M+2) caused by two labeled carbon atoms. In addition, another set of peaks that recorded from m/z = 13 to 16 exist both in the MS of ¹³C₂H₄ (¹³CH₂⁺, m/z = 15; ¹³CH⁺, m/z = 14; ¹³C⁺, m/z = 13) and ¹³C₂H₆ (¹³CH₃⁺, m/z = 16; ¹³CH₂⁺, m/z = 15; ¹³CH⁺, m/z = 14; ¹³C⁺, m/z = 13), which can be attributed to fragments caused by broken carbon–carbon bonds.

**Fig. 4: Standard guidelines for isotope-tracing experiments in CO₂ photoreduction.**

When the potential products of CO₂ photoreduction are liquids such as alcohols or acids, we used the headspace injection method instead of airtight needles (see “Methods” for experimental details). The temperature of the HP-PLOT/Q column was raised to 120 °C to separate alcohols. The liquids suspected to be methanol or CH₃OH (RT at 6.14 min) and ethanol or CH₃CH₂OH (RT at 12.23 min) eluted after the air components (RT at 2.96 min), CO₂ (RT at 3.18 min), and H₂O (RT at 3.98 min) in TIC (Fig. 4c). The material at RT = 6.14 min was identified as ¹³CH₃OH based on two sets of peaks: one set at m/z = 29 to 33 and another set at m/z = 13 to 16 attributed to the molecular ions of ¹³CH₃OH⁺ (m/z = 33) and the fragment ions of ¹³CH₃O⁺ (m/z = 32), ¹³CH₂O⁺ (m/z = 31), ¹³CHO⁺ (m/z = 30), ¹³CHO⁺ (m/z = 29), ¹³CH₃⁺ (m/z = 16), ¹³CH₂⁺ (m/z = 15), ¹³CH⁺ (m/z = 14), and ¹³C⁺ (m/z = 13), respectively. It is important to note that the largest peak in the MS was ¹³CH₃O⁺ (m/z = 32) due to the easier dissociation of CH₃OH. It also exhibits a mass shift effect (M+1) compared to the non-isotope-labeled CH₃OH (Supplementary Fig. 13). Despite the fact that ¹³CH₃¹³CH₂OH also has its largest fragment ion peak at m/z = 32, the source of this peak is derived from the cleavage of the carbon–carbon bonds, generating hydrogenated ¹³CH₂OH⁺ instead of ¹³CH₃O⁺ as was the case for ¹³CH₃OH. Moreover, there is no distinct peak at m/z = 33 in the MS of ¹³CH₃¹³CH₂OH that matches ¹³CH₃OH. The MS of the ethanol fraction ¹³CH₃¹³CH₂OH also has a set of peaks at m/z from 43 to 48, matching the molecular ions of ¹³C₂H₅OH⁺ (m/z = 48) and fragment ions of ¹³C₂H₄O⁺ (m/z = 47), ¹³C₂H₃O⁺ (m/z = 46), ¹³C₂H₂O⁺ (m/z = 45), ¹³C₂HO⁺ (m/z = 44), and ¹³C₂O⁺ (m/z = 43). It exhibited a mass shift effect of (M+2) or (M+1) versus the non-isotope-labeled C₂H₅OH (Supplementary Fig. 14) and the single-isotope-labeled CH₃¹³CH₂OH (Supplementary Fig. 15), respectively, due to the two isotope-labeled carbon atoms in one molecule of ¹³CH₃¹³CH₂OH (Supplementary Fig. 16). All of these points mentioned above are sufficient enough to match the qualitative requirements for ¹³CH₃OH and ¹³CH₃¹³CH₂OH. Likewise, the potential products of carboxylic acids (HCOOH and CH₃COOH) could be separated by choosing a column (HP-FFAP) with stronger polarity (see “Methods” for experimental details). As shown in Fig. 4d, separation depends on the different molecular polarities between CH₃COOH, HCOOH, and the reactants of H₂O and CO₂. CH₃COOH has a relatively short retention time (RT at 8.07 min) than HCOOH (RT at 10.17 min), which elutes from the column after the air components (RT at 2.62 min) and H₂O (RT at 3.15 min). By analyzing the corresponding MS, the non-isotope-labeled CH₃COOH (Supplementary Fig. 17) possesses a molecular ion peak at m/z = 60 and two prominent fragment ion peaks at m/z = 43 and m/z = 45, while the corresponding molecular ion and fragment ions peak obtained from isotope-labeled ¹³CH₃¹³COOH shift to m/z = 62, m/z = 45, and m/z = 46, respectively. It reveals a difference in relative proportion compared to non-isotope-labeled CH₃COOH, even considering the isotope-induced mass shift effect (M+2). After checking the MS of CH₃¹³COOH (Supplementary Fig. 18), a molecular ion peak at m/z = 61 and two fragment ion peaks at m/z = 44 and m/z = 46 were obtained. The two fragment ions of CH₃¹³COOH (m/z = 44 and m/z = 46), as well as the corresponding fragment ions of ¹³CH₃¹³COOH (m/z = 45 and m/z = 46) and CH₃COOH (m/z = 43 and m/z = 45), are generated by carbon–carbon bond cleavage (COOH⁺) and dehydroxylation (CH₃CO⁺), respectively (Supplementary Fig. 19). In addition, the isotope-labeled H¹³COOH possesses H¹³COOH⁺ (m/z = 47) molecular ions and fragment ions including ¹³COOH⁺ (m/z = 46), ¹³COO⁺ (m/z = 45), H¹³CO⁺ (m/z = 30), and ¹³CO⁺ (m/z = 29), which exhibit a mass shift effect (M+1) compared to the non-isotope-labeled HCOOH (Supplementary Fig. 20).

The four methods mentioned above can identify reactants and products in CO₂ photoreduction reactions. However, this process requires multiple setups, and there is no standard strategy to separate and analyze all these products, reactants, and air components simultaneously. Even for the most reported photocatalytic CO₂ conversion process of CO₂ to CO, a mixture of O₂, N₂, CO, CH₄, CO₂, and water vapor cannot be completely separated with one column due to the irreversible adsorption of CO₂ in the HP-Molesieve column and poor separation of CO/N₂ in the HP-PLOT/Q column. To solve this problem, we designed a parallel connection system (Fig. 5a, see “Methods” for experimental details) containing both HP-Molesieve and HP-PLOT/Q columns. The diameters of the parallel GC columns were optimized to enable the components from different columns to queue into the MS detector separately. As shown in Fig. 5b, O₂ (RT at 1.79 min), N₂ (RT at 2.20 min), CH₄ (RT at 2.48 min), and CO (RT at 4.59 min) elute from HP-Molesieve one by one and generate the corresponding MS spectra (Fig. 5c). It matches the abovementioned standard MS in Fig. 4a, respectively. CO₂ and H₂O could not be resolved by the HP-Molesieve channel but could be measured in the parallel HP-PLOT/Q channel. They eluted in the HP-PLOT/Q channel as an N₂/O₂/CO mixture (RT at 10.68 min), CH₄ (RT at 11.10 min), CO₂ (RT at 12.03 min), and H₂O (RT at 16.91 min), which matches the standard MS in Fig. 4b. Based on this parallel strategy, the simulated mixture from reagents to products to air components in the potential photocatalytic CO₂ reduction process could be analyzed in one GC-MS experiment.

**Fig. 5: A developed strategy of parallel connection system.**

Testing the isotope-tracing protocol using samples generated by well-studied CO₂ photoreduction reactions

After optimizing our isotope-tracing methods using multiple standard samples, we tried to verify its reliability using some previously reported photoreduction systems. The homogeneous molecular catalyst Fe^III porphyrin complex was used to evaluate CO₂ photoreduction (see “Methods” for experimental details) in a closed gas circulation system (Supplementary Fig. 21)⁵⁹. As shown in Fig. 6a, the obtained TIC of this system is similar to the standard spectra (Fig. 4a) because CH₄ and CO are products of this reaction. In MS, the molecular ion peaks, as well as the fragment ion peaks, were assigned to the isotopically labeled ¹³CH₄ and ¹³CO, respectively, conclusively demonstrating that the products of CH₄ and CO originated from the photoreduction of labeled ¹³CO₂ (Supplementary Fig. 22). Bipyridine complexes of ruthenium (Ru(bpy)₃Cl₂) is also a common homogeneous catalyst for CO₂ photoreduction. By comparison with the sample without reaction (Supplementary Fig. 23), we could confirm that the ¹³CO product comes from the reduction of CO₂ but not from the interfering factor of reactants (fragment ions from ¹³CO₂) (see “Methods” for experimental details). We also examined CO₂ photoreduction using a heterogeneous reaction system with Cd-doped ZnS as the photocatalyst. Cd-doped ZnS can reduce CO₂ into HCOOH under light irradiation and was used to validate our GC-MS isotope-tracing method for liquid-phase products (see “Methods” for experimental details)⁶⁰. Fig. 6 shows the TIC (Fig. 6c) and MS spectrum (Fig. 6d) collected using the products. The peak at RT = 10 min in the TIC corresponded to three peaks in the MS that match our standard MS for H¹³COOH (Fig. 4b). These results demonstrate that our method is also capable of tracing liquid products generated by CO₂ reduction.

**Fig. 6: Isotope-tracing experiments in reported homogeneous and heterogeneous photoreduction systems.**

In addition, isotope tracing in all-organic reaction systems is particularly difficult to assess in CO₂ photoreduction experiments. We employed our recently reported conjugated polymers (CPs) as a representative photocatalyst to experiment with both gas–solid phases (Supplementary Fig. 24) (see “Methods” for experimental details) and liquid phase (Supplementary Fig. 25) (see “Methods” for experimental details) reactions³⁴. Only an increase in CO could be observed during the liquid phase reaction by comparing the TIC before and after photoreduction (Fig. 7a), and the MS collected at RT = 4.59 min matches the standard MS of ¹³CO (Fig. 7b), implying that CO originates from CO₂ reduction (Supplementary Fig. 26). In contrast, CPs in the gas phase reaction possesses much higher activities and produces additional CH₄ compared to the liquid phase reaction. In the corresponding MS (inset of Fig. 6c), CO and CH₄ are primarily generated by photothermal effect-induced decomposition on solid CP instead of CO₂ photoreduction (Supplementary Fig. 27). This result leaves little doubt that the self-decomposition of catalyst can seriously affect both the qualitative and quantitative analysis of the product when evaluating the CO₂ photoreduction in the gas-solid phase of CPs. It also illustrates the importance of accurate isotope-tracing methods to prove the efficiency of CO₂ photoreduction in different materials systems. Moreover, it should be emphasized that the isotope experiments and accurate GC-MS tests are not only necessary for the reaction systems using sacrificial agents but also important for the reaction systems without sacrificial agents.

**Fig. 7: Isotope-tracing experiments in reported liquid and gas–solid phase photoreduction systems.**

Discussion

In summary, we initially demonstrated the difficulty of accurately ascribing products of CO₂ photoreduction in isotope-tracing experiments. Existing methods are known to be rather crude due to the similarity of reactants, products, and the catalyst itself, which negatively affects efforts toward reliable CO₂ photoreduction processes. Thus we sought to develop a rigorous strategy to eliminate the false-positive results by providing solid evidence of CO₂ photoreduction. We disclosed many often neglected false-positive results in isotope-tracing studies using standard isotopically labeled molecules and the basic principles of GC-MS analysis. Through extensive testing, we systematically presented isotope-tracer experiments methods of standard spectra for various potential products of CO, alkanes, alcohols, carboxylic acids, and alkenes. Then we devised a method to simultaneously analyze these potential products using a parallel connection system using two GC columns. The accuracy of this parallel setup was verified with the standard isotopes described earlier; then, the setup was used to analyze four previously reported systems for CO₂ photoreduction. The purpose of this research is to highlight appropriate scientific methods in CO₂ photoreduction, help researchers avoid the pitfalls and misunderstandings in isotope-tracing experiments, and propose some standard procedures. More precise procedures will allow researchers to provide better feedback in their efforts to design photocatalysts with high selectivities and conversion efficiencies for CO₂ photoreduction. We also provide examples and reference measurements for the ¹³C isotopes of numerous known reactants and products to help researchers firmly attribute them to CO₂ reduction reactions.

Methods

Using HP-5ms as a column for isotope-labeled samples analysis

The 0.5 ml gas samples were collected and injected by gas-tight syringes (the VICI Pressure-Lok Precision Analytical Syringe A-2 Series (050033), 1 ml) and then analyzed by gas chromatography-mass spectrometry (8890-5977B GC-MS instrument, Agilent Technologies, USA) equipped with most used commercial capillary columns (HP-5ms, 5%-Phenyl-methylpolysiloxane, 19091S-433UI-KEY, 30 m × 0.25 mm × 25 μm, Agilent Technologies, USA) in GC-MS. Helium was used as carrier gas. The column was maintained at 150 °C for 25 min, and the flow of the carrier was 0.8 ml l⁻¹. The temperatures of the injector, EI source, and GCITF were set to be 200, 200, and 250 °C, respectively. The selected mass-to-charge ratios of ions were 17, 29, and 45 in SIM mode. Developing a suitable programmed temperature rise process can further shorten the detection time.

Using SVUV-PIMS for isotope-labeled samples analysis

The synchrotron VUV photoionization mass spectroscopy (SVUV-PIMS) experiments were performed on the combustion station of the National Synchrotron Radiation Laboratory (Hefei, China). The test modes are the photoionization energy scan under the determined mass-to-charge ratio and the mass-to-charge ratio scan under the determined photoionization energy, respectively. Synchrotron radiation from the undulator beamline was monochromatized with 200 lines/mm laminar grating (Horiba Jobin Yvon, France), which covered the photon energy from 7.5 to 22 eV with an energy resolving power of 3000 (E/∆E at 10 eV). The average photon flux could reach the magnitude of 1013 photons/s after suppressing the higher-order harmonic radiation by a gas filter filled with noble gas^61,62.

Using different columns for isotope-labeled samples analysis

The 0.5 ml gas samples were collected and injected by gas-tight syringes (the VICI Pressure-Lok Precision Analytical Syringe A-2 Series (050033), 1 ml), and the 2 ml liquid samples were collected and placed in a headspace sampler; then the samples were analyzed by gas chromatography-mass spectrometry (8890-5977B GC-MS instrument, Agilent Technologies, USA) equipped with commercial capillary columns. The column was maintained at a certain temperature for 15 min, and the flow of the carrier was 0.8 ml l⁻¹. The temperatures of the injector, EI source, and GCITF were set to be 200, 200, and 250 °C, respectively. The mass-to-charge ratio of the mass scanning mode was set from 2 to 70. The GC-MS was operated the post-run after each injection (the temperature of the column oven increased to 300 °C with a rate of 30 °C and then maintained at 300 °C for 10 min). Developing a suitable programmed temperature rise process can further shorten the detection time.

The information of the columns are listed below:

(HP-Molesieve, 5A molesieve, 19091S-MS8, 30 m × 0.32 mm × 25 μm, Agilent Technologies, USA; HP-PLOT/Q, Bonded polystyrene-divinylbenzene, 19091P-QO4, 30 m × 0.32 mm × 20 μm, Agilent Technologies, USA; HP-FFAP, Modified polyethylene glycol, 19091F-413, 30 m × 0.32 mm × 20 μm, Agilent Technologies, USA).

Using a designed parallel connection system as a column for isotope-labeled samples analysis

The 0.5 ml gas samples were collected and injected by gas-tight syringes (the VICI Pressure-Lok Precision Analytical Syringe A-2 Series (050033), 1 ml) and then analyzed by gas chromatography-mass spectrometry (8890-5977B GC-MS instrument, Agilent Technologies, USA) equipped with designed parallel connection system (HP-Molesieve 15 m × 0.53 mm × 20 μm, HP-PLOT/Q 15 m × 0.32 mm × 20 μm, and CP4016 10 m × 0.32 mm, Agilent Technologies, USA) in GC-MS. Helium was used as carrier gas. The column was maintained at 45 °C for 20 min, and the flow of the carrier was 0.8 ml l⁻¹. The temperatures of the injector, EI source, and GCITF were set to be 200, 200, and 250 °C, respectively. The mass-to-charge ratio of the mass scanning mode was set from 2 to 70. The GC-MS was operated the post-run after each injection (the temperature of the column oven increased to 300 °C with a rate of 30 °C and then maintained at 300 °C for 10 min). Developing a suitable programmed temperature rise process can further shorten the detection time.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

References

Lin, H., Luo, S., Zhang, H. & Ye, J. Toward solar-driven carbon recycling. Joule 6, 294–314 (2022).
Article CAS Google Scholar
Wu, H. L., Li, X. B., Tung, C. H. & Wu, L. Z. Semiconductor quantum dots: an emerging candidate for CO₂ photoreduction. Adv. Mater. 31, 1900709 (2019).
Article Google Scholar
Li, X., Yu, J., Jaroniec, M. & Chen, X. Cocatalysts for selective photoreduction of CO₂ into solar fuels. Chem. Rev. 119, 3962–4179 (2019).
Article CAS PubMed Google Scholar
Li, R., Zhang, W. & Zhou, K. Metal-organic‐framework‐based catalysts for photoreduction of CO₂. Adv. Mater. 30, 1705512 (2018).
Article Google Scholar
Wang, H.-N. et al. Recent progress and perspectives in heterogeneous photocatalytic CO₂ reduction through a solid-gas mode. Coord. Chem. Rev. 438, 213906 (2021).
Article CAS Google Scholar
Jiao, X. et al. Fundamentals and challenges of ultrathin 2D photocatalysts in boosting CO₂ photoreduction. Chem. Soc. Rev. 49, 6592–6604 (2020).
Article CAS PubMed Google Scholar
Chang, X., Wang, T. & Gong, J. CO₂ photo-reduction: insights into CO₂ activation and reaction on surfaces of photocatalysts. Energy Environ. Sci. 9, 2177–2196 (2016).
Article CAS Google Scholar
Gong, E. et al. Solar fuels: research and development strategies to accelerate photocatalytic CO₂ conversion into hydrocarbon fuels. Energy Environ. Sci. 15, 880–937 (2022).
Article CAS Google Scholar
Keith, D. W. Why capture CO₂ from the atmosphere? Science 325, 1654–1655 (2009).
Article ADS CAS PubMed Google Scholar
Chen, C., Kotyk, J. F. K. & Sheehan, S. W. Progress toward commercial application of electrochemical carbon dioxide reduction. Chem 4, 2571–2586 (2018).
Article CAS Google Scholar
Lewis, N. S. & Nocera, D. G. Powering the planet: chemical challenges in solar energy utilization. Proc. Natl Acad. Sci. USA 103, 15729–15735 (2006).
Article ADS CAS PubMed PubMed Central Google Scholar
Hoffert, M. I. et al. Advanced technology paths to global climate stability: energy for a greenhouse planet. Science 298, 981–987 (2002).
Article ADS CAS PubMed Google Scholar
Jiao, X., Zheng, K., Hu, Z., Sun, Y. & Xie, Y. Broad-spectral-response photocatalysts for CO₂ reduction. ACS Cent. Sci. 6, 653–660 (2020).
Article CAS PubMed PubMed Central Google Scholar
Ozin, G. A. Throwing new light on the reduction of CO₂. Adv. Mater. 27, 1957–1963 (2015).
Article CAS PubMed Google Scholar
Pougin, A. et al. Au@TiO₂ core-shell composites for the photocatalytic reduction of CO₂. Chemistry 24, 12416–12425 (2018).
Article CAS PubMed Google Scholar
Dulla, M., Pougin, A. & Strunk, J. Evaluation of the plasmonic effect of Au and Ag on Ti-based photocatalysts in the reduction of CO₂ to CH₄. J. Energy Chem. 26, 277–283 (2017).
Article Google Scholar
Moustakas, N. G. & Strunk, J. Photocatalytic CO₂ reduction on TiO₂-based materials under controlled reaction conditions: systematic insights from a literature study. Chemistry 24, 12739–12746 (2018).
Article CAS PubMed Google Scholar
Lee, B. H. et al. Electronic interaction between transition metal single-atoms and anatase TiO₂ boosts CO₂ photoreduction with H₂O. Energy Environ. Sci. 15, 601–609 (2022).
Article CAS Google Scholar
Zhang, L., Zhao, Z.-J., Wang, T. & Gong, J. Nano-designed semiconductors for electro-and photoelectro-catalytic conversion of carbon dioxide. Chem. Soc. Rev. 47, 5423–5443 (2018).
Article CAS PubMed Google Scholar
Jiang, Z. et al. Filling metal-organic framework mesopores with TiO₂ for CO₂ photoreduction. Nature 586, 549–554 (2020).
Article ADS CAS PubMed Google Scholar
Yu, H. et al. Synergy of ferroelectric polarization and oxygen vacancy to promote CO₂ photoreduction. Nat. Commun. 12, 4594 (2021).
Article ADS CAS PubMed PubMed Central Google Scholar
Sahm, C. D., Ucoski, G. M., Roy, S. & Reisner, E. Automated and continuous-flow platform to analyze semiconductor-metal complex hybrid systems for photocatalytic CO₂ reduction. ACS Catal. 11, 11266–11277 (2021).
Article CAS Google Scholar
Cortes, M. A. L. et al. Formal quantum efficiencies for the photocatalytic reduction of CO₂ in a gas phase batch reactor. Catal. Today 326, 75–81 (2019).
Article CAS Google Scholar
Li, K., An, X., Park, K. H., Khraisheh, M. & Tang, J. A critical review of CO₂ photoconversion: catalysts and reactors. Catal. Today 224, 3–12 (2014).
Article CAS Google Scholar
Christopher, P., Jin, S., Sivula, K. & Kamat, P. V. Why seeing is not always believing: common pitfall in photocatalysis and electrocatalysis. ACS Energy Lett. 6, 707–709 (2021).
Article CAS Google Scholar
Yang, C. C., Vernimmen, J., Meynen, V., Cool, P. & Mul, G. Mechanistic study of hydrocarbon formation in photocatalytic CO₂ reduction over Ti-SBA-15. J. Catal. 284, 1–8 (2011).
Article CAS Google Scholar
Mei, B., Pougin, A. & Strunk, J. Influence of photodeposited gold nanoparticles on the photocatalytic activity of titanate species in the reduction of CO₂ to hydrocarbons. J. Catal. 306, 184–189 (2013).
Article CAS Google Scholar
Das, R., Chakraborty, S. & Peter, S. C. Systematic assessment of solvent selection in photocatalytic CO₂ reduction. ACS Energy Lett. 6, 3270–3274 (2021).
Article CAS Google Scholar
Zhang, Y. et al. Photocatalytic CO₂ reduction: identification and elimination of false-positive results. ACS Energy Lett. 7, 1611–1617 (2022).
Article CAS Google Scholar
Chen, P. et al. Rapid self-decomposition of g-C₃N₄ during gas-solid photocatalytic CO₂ reduction and its effects on performance assessment. ACS Catal. 12, 4560–4570 (2022).
Article CAS Google Scholar
Yang, C. C., Yu, Y. H., van der Linden, B., Wu, J. C. & Mul, G. Artificial photosynthesis over crystalline TiO₂-based catalysts: fact or fiction? J. Am. Chem. Soc. 132, 8398–8406 (2010).
Article CAS PubMed Google Scholar
Cybula, A., Klein, M. & Zaleska, A. Methane formation over TiO₂-based photocatalysts: reaction pathways. Appl. Catal. B Environ. 164, 433–442 (2015).
Article CAS Google Scholar
Xu, F. et al. Unique S-scheme heterojunctions in self-assembled TiO₂/CsPbBr₃ hybrids for CO₂ photoreduction. Nat. Commun. 11, 4613 (2020).
Article ADS CAS PubMed PubMed Central Google Scholar
Wang, S. et al. Intermolecular cascaded π-conjugation channels for electron delivery powering CO₂ photoreduction. Nat. Commun. 11, 1149 (2020).
Article ADS PubMed PubMed Central Google Scholar
Li, Y. et al. Facile top-down strategy for direct metal atomization and coordination achieving a high turnover number in CO₂ photoreduction. J. Am. Chem. Soc. 142, 19259–19267 (2020).
Article CAS PubMed Google Scholar
Hawecker, J., Lehn, J.-M. & Ziessel, R. Efficient photochemical reduction of CO₂ to CO by visible light irradiation of systems containing Re(bipy)(CO)₃X or Ru(bipy)₃²⁺-Co²⁺ combinations as homogeneous catalysts. J. Chem. Soc., Chem. Commun. 9, 536–538 (1983).
Lecomte, J.-P., Lehn, J.-M., Parker, D., Guilhem, J. & Pascard, C. A dinuclear rhodium-carbonyl cryptate of a ditopic macrocyclic ligand. J. Chem. Soc., Chem. Commun. 6, 296–298 (1983).
Willner, I. & Mandler, D. Characterization of palladium-. beta.-cyclodextrin colloids as catalysts in the photosensitized reduction of bicarbonate to formate. J. Am. Chem. Soc. 111, 1330–1336 (1989).
Article CAS Google Scholar
Chatterjee, T., Boutin, E. & Robert, M. Manifesto for the routine use of NMR for the liquid product analysis of aqueous CO₂ reduction: from comprehensive chemical shift data to formaldehyde quantification in water. Dalton Trans. 49, 4257–4265 (2020).
Article CAS PubMed Google Scholar
Kuhl, K. P. et al. Electrocatalytic conversion of carbon dioxide to methane and methanol on transition metal surfaces. J. Am. Chem. Soc. 136, 14107–14113 (2014).
Article CAS PubMed Google Scholar
Fu, Z. et al. A stable covalent organic framework for photocatalytic carbon dioxide reduction. Chem. Sci. 11, 543–550 (2020).
Article CAS PubMed Google Scholar
Li, J. et al. Self-adaptive dual-metal-site pairs in metal-organic frameworks for selective CO₂ photoreduction to CH₄. Nat. Catal. 4, 719–729 (2021).
Article CAS Google Scholar
Diercks, C. S., Liu, Y., Cordova, K. E. & Yaghi, O. M. The role of reticular chemistry in the design of CO₂ reduction catalysts. Nat. Mater. 17, 301–307 (2018).
Article ADS CAS PubMed Google Scholar
Schoedel, A., Ji, Z. & Yaghi, O. M. The role of metal–organic frameworks in a carbon-neutral energy cycle. Nat. Energy 1, 16034 (2016).
Article ADS CAS Google Scholar
Nguyen, H. L. & Alzamly, A. Covalent organic frameworks as emerging platforms for CO₂ photoreduction. ACS Catal. 11, 9809–9824 (2021).
Article CAS Google Scholar
Fang, Z.-B. et al. Boosting interfacial charge-transfer kinetics for efficient overall CO₂ photoreduction via rational design of coordination spheres on metal–organic frameworks. J. Am. Chem. Soc. 142, 12515–12523 (2020).
Article CAS PubMed Google Scholar
Wang, J.-W. et al. Facile electron delivery from graphene template to ultrathin metal-organic layers for boosting CO₂ photoreduction. Nat. Commun. 12, 813 (2021).
Article ADS CAS PubMed PubMed Central Google Scholar
Dai, C. & Liu, B. Conjugated polymers for visible-light-driven photocatalysis. Energy Environ. Sci. 13, 24–52 (2020).
Article CAS Google Scholar
Huang, Q. et al. Multielectron transportation of polyoxometalate-grafted metalloporphyrin coordination frameworks for selective CO₂-to-CH₄ photoconversion. Natl Sci. Rev. 7, 53–63 (2020).
Article CAS PubMed Google Scholar
Wang, Y., Godin, R., Durrant, J. R. & Tang, J. Efficient hole trapping in carbon dot/oxygen‐modified carbon nitride heterojunction photocatalysts for enhanced methanol production from CO₂ under neutral conditions. Angew. Chem. Int. Ed. 60, 20811–20816 (2021).
Article CAS Google Scholar
Gao, W. et al. Vacancy-defect modulated pathway of photoreduction of CO₂ on single atomically thin AgInP₂S₆ sheets into olefiant gas. Nat. Commun. 12, 4747 (2021).
Article ADS CAS PubMed PubMed Central Google Scholar
Ni, B., Jiang, H., Guo, W., Xu, Q. & Min, Y. Tailoring the oxidation state of metallic TiO through Ti³⁺/Ti²⁺ regulation for photocatalytic conversion of CO₂ to C₂H₆. Appl. Catal. B Environ. 307, 121141 (2022).
Shao, W. et al. In-plane heterostructure Ag₂S-In₂S₃ atomic layers enable boosted CO₂ photoreduction into CH₄. Nano Res. 14, 4520–4527 (2021).
Article ADS CAS Google Scholar
Zhang, K. et al. Current dilemma in photocatalytic CO₂ reduction: real solar fuel production or false positive outcomings? Carb. Neutrality 1, 10 (2022).
Article Google Scholar
Vestal, M. L. Methods of ion generation. Chem. Rev. 101, 361–376 (2001).
Article CAS PubMed Google Scholar
Khan, I. S. et al. An efficient metal-organic framework‐derived nickel catalyst for the light driven methanation of CO₂. Angew. Chem. Int. Ed. 60, 26476–26482 (2021).
Article CAS Google Scholar
Adams, N. G., Poterya, V. & Babcock, L. M. Electron molecular ion recombination: product excitation and fragmentation. Mass Spectrom. Rev. 25, 798–828 (2006).
Article ADS CAS PubMed Google Scholar
Xu, J. et al. Efficient infrared‐light‐driven CO₂ reduction over ultrathin metallic Ni‐doped CoS₂ nanosheets. Angew. Chem. Int. Ed. 60, 8705–8709 (2021).
Article CAS Google Scholar
Rao, H., Schmidt, L. C., Bonin, J. & Robert, M. Visible-light-driven methane formation from CO₂ with a molecular iron catalyst. Nature 548, 74–77 (2017).
Article ADS CAS PubMed Google Scholar
Meng, X. et al. Efficient photocatalytic CO₂ reduction in all-inorganic aqueous environment: cooperation between reaction medium and Cd (II) modified colloidal ZnS. Nano Energy 34, 524–532 (2017).
Article CAS Google Scholar
Zhou, Z. et al. The vacuum ultraviolet beamline/endstations at NSRL dedicated to combustion research. J. Synchrotron Radiat. 23, 1035–1045 (2016).
Article CAS PubMed Google Scholar
Pan, Y. et al. Online characterization of isomeric/isobaric compounds in the gas phase of mainstream cigarette smoke by synchrotron radiation vaccum ultraviolet photoionization time-of-flight mass spectrometry and photoionization efficiency curve simulation. Anal. Chem. 85, 11993–12001 (2013).
Article CAS PubMed Google Scholar

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Acknowledgements

This work received financial support from the National Science Foundation of China (Nos. 51902121, 52073110, 22106106, 22071072, 21975090, and 52003213), the World Premier International Research Center Initiative (WPI Initiative) on Materials Nanoarchitectonics (MANA), MEXT (Japan), KAKENHI (18H02065, 20K05453), MEXT, and Photoexcitonix Project in Hokkaido University, Japan, the Fundamental Research Funds for the Central Universities of China (2662022LXPY001, 2662018QD011, 2662018PY052, SZYJY2022012, and 2662019PY023), and the Natural Science Foundation of Hubei Province (2019CFB322).

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Authors and Affiliations

College of Science, Shenzhen Institute of Nutrition and Health, Huazhong Agricultural University, 430070, Wuhan, P. R. China
Shengyao Wang, Sirong Zou & Hao Chen
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan
Shengyao Wang, Joel Henzie, Xianguang Meng, Hui Song & Jinhua Ye
Shenzhen Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Genome Analysis Laboratory of the Ministry of Agriculture, Agricultural Genomics Institute at Shenzhen, Chinese Academy of Agricultural Sciences, 518120, Shenzhen, P. R. China
Shengyao Wang
The Education Ministry Key Lab of Resource Chemistry, Joint International Research Laboratory of Resource Chemistry, Shanghai Frontiers Science Center of Biomimetic Catalysis, College of Chemistry and Materials Science, Shanghai Normal University, 200234, Shanghai, China
Bo Jiang & Hexing Li
Laboratory of Solar Fuel, Faculty of Materials Science and Chemistry, China University of Geosciences, 430074, Wuhan, P. R. China
Feiyan Xu & Jiaguo Yu
National Synchrotron Radiation Laboratory, University of Science and Technology of China, 230029, Hefei, P. R. China
Chengyuan Liu & Yang Pan
Hebei Provincial Key Laboratory of Inorganic Nonmetallic Materials, College of Materials Science and Engineering, North China University of Science and Technology, 063210, Tangshan, P. R. China
Xianguang Meng
Graduates School of Chemical Science and Engineering, Hokkaido University, Sapporo, 060-0814, Japan
Jinhua Ye
TU-NIMS International Collaboration Laboratory, Tianjin University, 300072, Tianjin, P. R. China
Jinhua Ye

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Shengyao Wang
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Bo Jiang
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Hexing Li
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Contributions

S.W. and J.Ye. conceived the idea and designed the experiments; S.W. established methods for GC-MS analysis; S.W. and B.J. designed the parallel connection system; S.W., H.S., and S.Z. conducted GC-MS analysis for isotope-labeled standard samples; F.X., C.L., and Y.P. conducted the SVUV-PIMS measurements; S.W., X.M., and B.J. performed the isotopic experiments over reported systems. S.W., J.H., and B.J. wrote the manuscript; H.L., J.Yu., H.C., and J.Ye. jointly supervised the work and revised the manuscript. All authors contributed to the discussion of the results and the manuscript preparation.

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Correspondence to Bo Jiang, Jiaguo Yu, Hao Chen or Jinhua Ye.

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Wang, S., Jiang, B., Henzie, J. et al. Designing reliable and accurate isotope-tracer experiments for CO₂ photoreduction. Nat Commun 14, 2534 (2023). https://doi.org/10.1038/s41467-023-38052-0

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Received: 26 September 2022
Accepted: 13 April 2023
Published: 03 May 2023
DOI: https://doi.org/10.1038/s41467-023-38052-0

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