(Invited) Perspectives for Design of Active and Stable Oxygen Evolution Electrocatalysts

One of the key challenges for the large-scale application of electrochemical energy conversion, employing reactors for water electrolysis and CO2 reduction, is still relatively low energy-efficiency of the anodic oxygen evolution reaction (OER). Although, oxides are perceived to be representative class of compounds used as catalytic materials, after more than 40 years of intensive research on OER, it is still not clear what really determines activity and stability trends. At technically relevant current densities, the critical point for obtaining a conclusive picture about the electrode performance is to understand the dynamic behavior of the triple-phase boundary. Fluctuations in the magnitude of the active surface area, due to blockage of a fraction of the overall number of active sites by the gas, induces great uncertainty in kinetic analysis which is usually based on stationary electrochemical methods. Consequently, the task of the highest merit is to employ advanced analytical tools and create methodologies which allow realistic insight into dynamic behavior of the polarized electrode/electrolyte interface during the gas release. In this work, recently developed approaches for comprehensive activity/stability studies will be discussed. Namely, activity is estimated using scanning electrochemical microscopy (SECM) in a mode adjusted for local electrochemical noise measurements. A positioned microelectrode was used as a sensor in order to estimate/monitor the frequency of gas-bubble detachment from the electrode surface. Recorded potential-dependent frequency spectra are the fingerprints of temporal fluctuations at the electrode/electrolyte interface. At the same time stability analysis was conducted using a miniaturized  electrochemical scanning flow cell coupled to the inductively coupled mass spectrometer (SFC-ICPMS). Obtained time-resolved potential dependent dissolution profiles were used as indication of the character of the dissolution process. In the final section of the work, based on the information gathered from SECM and SFC-ICPMS, was proposes a design of the electrode surface which could help to achieve the elusive goal of having simultaneously highly active and highly stable catalysts for the oxygen evolution reaction.

Acknowledgment. BMBF for the financial support in the framework of the project ECCO2 (Kz: 033RC1101A).

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