Electrochemical (EC) CO2
fixation and conversion are of great significance for enabling green
synthesis and achieving carbon neutrality. Homogeneous metal
complex-mediated CO2 reduction systems feature highly complex
reaction pathways that evolve rapidly in response to external
conditions and applied potentials, calling for spatiotemporally coupled
in situ mass spectrometry (MS) capable of characterizing key
intermediates and monitoring multiple reaction species in real time.
However, the intrinsic conflict between the operational requirements of
MS ionization and those of EC reactions has long hindered their highly
spatiotemporal coupling. In this study, we introduce a floating-ground
electrochemical electrospray ionization (FE-ESI) strategy that enables
continuous and precise control and measurement of EC potential/current
during ESI-MS analysis, fundamentally resolving the long-standing
challenge of their spatiotemporal coupling. The resulting system has
allowed EC as well as MS detection and characterization of
microsecond-scale transient intermediates before they undergo further
transformation. In the study of phenanthroline-copper complex-catalyzed
CO2 reduction, we successfully captured a series of reactive
copper cluster intermediates, directly verified─for the first time in
experiment─the Girard isomerization process of the phenanthroline-copper
catalyst, and elucidated the underlying mechanism by which the ligand
and copper center cooperatively regulate CO2 reduction selectivity. (DOI：10.1021/jacs.6c02004)