Evaluating Differential Electrochemical Mass Spectrometry as a Tool to Probe the Lattice Oxygen Exchange Mechanism of Oxygen Evolution at Transition Metal Oxide Catalysts

Abstract Differential electrochemical mass spectrometry (DEMS) is often employed to identify whether electrochemical oxygen evolution (OER) at transition metal oxides proceeds via the participation of lattice oxygen. In the corresponding experiments, OER is conducted when either the metal oxide or the electrolyte is enriched with 18 O. If the mol fraction of 16 O 18 O ( χ ( 16 O 18 O)) in the evolved oxygen deviates from the value expected from the isotopic composition of the electrolyte, the lattice oxygen exchange mechanism is considered proven. However, it is unclear whether this mechanism can be excluded if χ ( 16 O 18 O) does not deviate from the expected value, because the DEMS set‐up may lack the sensitivity required to observe this mechanism. In this work, we develop a model that predicts χ ( 16 O 18 O) as a function of the charge passed due to OER. This allows evaluation of the conditions and the level of confidence with which the lattice exchange mechanism can be excluded. We employ this model to show that less than 10% (if any) of OER at CoCr 2 O 4 , Co 2 CrO 4 , RuO 2 and Ru, respectively, forms via the lattice exchange mechanism during water electrolysis at room temperature. Finally, we discuss how experimental pitfalls may lead to results that erroneously indicate OER via the lattice exchange mechanism.