{
  "abstract": "It has been a long-standing challenge in electrocatalysis to measure product formation with kinetically relevant time resolution. Here, we couple a real-time gas analyzer mass spectrometer with a modified sampling inlet to a gas diffusion electrode cell, achieving sub-second time resolution for both reactant consumption and product formation. We focus on CO 2 /CO reduction on oxide-derived Cu, motivated by the continuing interest in its reaction mechanism and its high selectivity to ethylene (C 2 H 4 ) formation. Potential step experiments for CO reduction reveal that the initial consumption of CO is fast (< 1 s), but the appearance of C 2 H 4 products can be 10 times slower, which we attribute to the time required for CO storage on the Cu surface and subsequent reconstruction into the active, C 2+ -forming, configuration. Previous studies have reported that the co-feed of 12 CO 2 / 13 CO results in the enhancement of 13 C-containing ethylene isotopologues, but the mechanism causing this remains unknown. Isotopic-labeled gas switching ( 12 CO 2 - 13 CO) experiments yield compelling evidence that 13 C species continue to exist for more than a minute at near proximity to or on the catalyst, even after the supply source has been cut off, evidenced by the significant enhancement of 13 C-containing ethylene isotopologues: pure ( 13 C 2 H 4 ) and mixed ( 13 C 12 CH 4 ), formed through a CO 2 (g)-*CO pathway. Importantly, the size of the C 1 reservoir, the amount of 13 C 12 CH 4 made when CO 2 reacts with it, and the amount of Cu + that is removed are all in the micromole range. Thus, the picture emerges that a monolayer is stripped off from the copper catalyst surface during the CO-CO 2 switch. Tracking of dynamic Cu surface insights (i.e., activation, dissolution and deactivation) provides valuable mechanistic insights for optimizing reaction conditions.",
  "abstract_shown": true,
  "affiliations": [
    "Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, United States, 94720",
    "Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, United States, 94720",
    "Materials Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, United States, 94720",
    "Department of Materials Science and Engineering, University of California, Berkeley, 210 Hearst Memorial Mining Building, Berkeley, CA, United States, 94720"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Helen J. Zeng",
      "orcid": "0000-0002-1850-4923"
    },
    {
      "affs": [
        0
      ],
      "name": "Yesol Kim",
      "orcid": "0000-0003-0864-2166"
    },
    {
      "affs": [
        1
      ],
      "name": "Junko Yano",
      "orcid": "0000-0001-6308-9071"
    },
    {
      "affs": [
        0,
        2,
        3
      ],
      "name": "Joel W. Ager",
      "orcid": "0000-0001-9334-9751"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ezx2gxc26dzvx.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15008486/v1",
  "fulltext_url": null,
  "id": "ezx2gxc26dzvx",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008486/v1",
  "language": null,
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2105|CO2 Reduction Techniques and Catalysts"
    ]
  ],
  "openalex": "W7211963999",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15008486/v1",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-08",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/ezx2gxc26dzvx.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:17Z",
      "native_id": "10.26434/chemrxiv.15008486",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008486/v1"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "source:chemrxiv",
      "subfield": "general"
    }
  ],
  "title": "Fast-Response Operando Mass Spectrometry Demystifies C₂ Product Formation in Cu-Catalyzed CO and CO₂ Reduction: Burst of Ethylene Isotopologues",
  "title_text": "Fast-Response Operando Mass Spectrometry Demystifies C₂ Product Formation in Cu-Catalyzed CO and CO₂ Reduction: Burst of Ethylene Isotopologues",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:17Z",
  "url": "https://research.draconitic.com/paper/ezx2gxc26dzvx",
  "venue": "ChemRxiv",
  "versions": []
}