Dynamic Activity and Stability of Transition Metal (oxy)Hydroxide Oxygen Evolution Electrocatalysts Under Steady and Intermittent Operation
Authors: Marquez Raul A. , Le Thuy Vy , Espinosa Michael , Ko Daniel Y , Kawashima Kenta , Bender Jay T , Dolocan Andrei , Miller Nathan , Milliron Delia , Resasco Joaquin , Mullins Charles Buddie 
Published: August 2024

The oxygen evolution reaction (OER) plays a critical role in several energy conversion technologies, requiring catalysts that combine high activity with stability for successful commercialization. Catalysts from first-row transition metal oxides have garnered considerable attention in this context. Their noteworthy OER activity and stability in alkaline environments position them as a more economical option than their counterparts in acidic media. However, recent studies have shown that these materials tend to experience significant dissolution issues and undergo changes in their chemical composition, a phenomenon observed even during steady-state operation.1–3 Addressing these challenges is essential for advancing commercial energy conversion technologies, which often face intermittent loads and reverse currents. A deeper understanding of the dynamic reconstruction under fluctuating conditions is crucial for developing more durable and efficient electrocatalytic materials.4

In this work, we investigate the dynamic performance of nickel cobalt (oxy)hydroxide electrocatalytic films containing iron active sites in alkaline media under steady and intermittent operation. First, we systematically examine the changes in OER catalytic activity in a typical three-electrode configuration, focusing on the incorporation and redissolution of iron and cerium during different electrochemical conditioning methods. As shown in Figure 1a, conditioning using chronopotentiometry decreases the OER overpotential without significantly shifting the redox peak. In contrast, conditioning using cyclic voltammetry significantly shifts the redox peak position (Figure 1b). These differences are attributed to the (oxy)hydroxide film thickness, which forms in situ during conditioning and affects the Fe dissolution and incorporation rates based on the conditioning method.5 We use different analytical techniques to probe chemical transformations during conditioning. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS) are utilized to analyze compositional changes in the electrocatalytic films. Moreover, inductively coupled plasma mass spectrometry (ICP-MS) tracks metal dissolution.
Next, we utilize an electrochemical flow electrolyzer with a zero-gap configuration, integrated with online ICP-MS and post-experimental TOF-SIMS and XPS, to study the reconstruction of these electrocatalysts under intermittent conditions. A NiFe anode operating in 6 M KOH with 1 ppm of Fe3+ shows a 40-mV change after 120 cycles of alternating low and high currents, including a simulated shutdown step (Figure 1c). This cell potential change, becoming more negative with continued cycling (Figure 1d), is attributed to the shutdown step. Our findings underscore how operating conditions affect the dynamic reconstruction of electrocatalytic materials, offering critical insights for developing more robust and resilient materials suitable for commercial applications.

References:

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Figure 1