LAUSR

Abstract The in situ detection of the product of the oxygen evolution reaction (OER) catalyzed by cobalt phosphate (CoPi) was achieved with interdigitated array (IDA) electrodes. For this purpose, CoPi and Pt were electrodeposited on the two working electrodes of an IDA, the generator and the collector. The CoPi-catalyzed OER could then be analyzed on the IDA generator and the reaction product, O2, could be detected immediately by the closely arrayed Pt IDA collector electrode. The CoPi-Pt IDA reveals a clear O2 evolution process corresponding to the different oxidation states of the catalyst for the OER and provides information regarding the existence of higher cobalt oxidation states. The turnover frequencies are also calculated using the IDA results. In addition, continuous O2 production and detection was achieved by holding the CoPi generator at a constant higher potential with the Pt collector at a reducing potential measuring O2 from the generator. The collection efficiency is above 90%, meaning that 90% of the O2 product is measured in situ by the IDA collector. Other electrocatalytic reactions of interest could be similarly investigated both qualitatively and quantitatively using IDA electrodes operating in the generator–collector mode.