Understanding Electrochemical CO₂ Reduction through Differential Electrochemical Mass Spectrometry

The electrochemical reduction of CO₂ powered by renewable energy is a viable pathway to produce valuable fuels and chemicals, while simultaneously helping to mitigate greenhouse gas emissions. The strong research interest in improving the selectivity and efficiency of CO₂ reduction has led to a multitude of electrocatalyst studies that employ a variety of electrochemical, spectroscopic, spectrometric, and materials characterization analytical techniques. Among these, differential electrochemical mass spectrometry (DEMS) has become an increasingly instrumental tool for investigating electrocatalyst performance by enabling in situ volatile product detection. DEMS has the significant advantages of being able to rapidly screen product distributions in real time as the potential is varied and distinguishing isotopically labeled species for mechanistic studies. There are also challenges for employing DEMS to study CO₂ reduction, including cell design limitations for optimal mass transport and high product ion current signal, a lack of nonvolatile product detection, and the difficulty of extracting reliable, quantitative faradaic efficiency measurements. Many researchers have applied DEMS to study the reduction of CO₂ on numerous catalysts under a variety of conditions, highlighting cell designs and protocols for overcoming some of these challenges. This review focuses on the implementation of DEMS in the study of electrochemical CO₂ reduction, explaining the working principle and the various commonly employed cell designs and highlighting the findings of key reports that were enabled by DEMS.