Differential electrochemical mass spectrometry (DEMS) is an analytical technique where a mass spectrometer is interfaced with an electrochemical reactor using a pervaporation membrane. This configuration enables volatile electrochemical reaction products to be continuously collected, identified, and quantified during constant or dynamic polarization. The detection sensitivity and time response of the technique are dependent on the proximity of the pervaporation membrane to the electrocatalyst surface. In our group, we coat the pervaporation membrane with the electrocatalyst via sputter deposition, which enables sampling to be performed directly from the electrode-electrolyte interface. This configuration maximizes both the detection sensitivity and time response while also enabling the composition of the local reaction environment to be directly observed. We have used this approach to quantify the potential dependent CO₂ reduction activity of monometallic electrocatalysts during linear sweep voltammetry at scan rates of up to 100 mV/s. Furthermore, this configuration can detect nine of the most abundantly produced products of electrochemical CO₂ reduction over Cu, which collectively account for >75% of the charge passed at -1 V vs RHE. We are continuing to develop this technique in order to obtain insights into the variables that ultimately dictate electrocatalytic activity. 

(A) Schematic of a DEMS instrument. (B) Schematic of a DEMS reactor utilizing a working electrocatalyst coated directly onto the nanoporous pervaporation membrane. (C) Potential dependent CO2 reduction activity of monometallic Ag measured via DEMS during linear sweep voltammetry at 5 mV/s.