On-Line Mass Spectrometry Beyond Single-Peak Analysis: Resolving Spectral Overlap in Electrochemical CO 2 Reduction

On-line gas phase analysis is critical for understanding transient phenomena in electrochemical CO 2 reduction (eCO 2 R), yet conventional gas chromatography (GC) is inherently discontinuous, producing measurements at intervals of several minutes. On-line mass spectrometry (MS) offers substantially faster temporal resolution, but applications in eCO 2 R are complicated by severe spectral overlap between CO, CO 2 and C 2 H 4 , rendering single-fragment quantification unreliable for Cu-based catalysts, where CO and C 2 H 4 are produced simultaneously. Existing correction strategies, including CO 2 fragmentation subtraction and reduced ionization energy either fail under these conditions, or compromise measurement sensitivity. We present a multivariate matrix deconvolution approach which regresses product concentrations against a full mass spectrum (m/z = 1-65) via ordinary least squares, with calibration coefficients continuously updated against intermittent GC reference measurements. This yields coefficients of determination (R 2 ) of 0.99, 0.98, 0.99 and 0.99 for H 2 , CO, CH 4 and C 2 H 4 respectively, at a scan rate of approximately two seconds. An experimentally characterized first order plus dead time response (θ ≈ 22 s, τ ≈ 24 s) quantifies system transport limitations. Spatially resolved sampling further demonstrates non-uniform product distributions along a gas diffusion electrode. Together, these capabilities demonstrate a promising analytical platform for transient and spatially resolved eCO 2 R characterization with MS.