Electrochemical activation of Ni-based electrodes for the alkaline oxygen evolution reaction

The transition to renewable energy sources requires efficient and sustainable energy storage systems, such as green hydrogen produced by alkaline water electrolysis (AWE). To meet the rising demands, reducing cell potential and lowering manufacturing costs are crucial. The sluggish kinetics of the oxygen evolution reaction at the anode offers optimization potential by efficient electrocatalyst design. Here, electrochemical conditioning is a promising tool as it is easily applicable and versatile. Previously, electrochemical conditioning has already been used to study the oxide growth on Ni and Fe and to find a low-cost and highly active electrocatalyst from steel. However, the interplay of the conditioning and the Ni: Fe-ratio of the electrode, which is often stated as oxygen evolution reaction activity descriptor, is not fully understood yet. This raises the question of how activation, surface changes, and electrochemical conditioning parameters are correlated for a model electrode with a Ni: Fe ratio in the optimum regime, considering the influence of Fe from the electrolyte. Investigating this requires a suitable testing system. While reported analytical electrochemical flow cells with online downstream analysis (iEFCs) are valuable for studying activity and stability, their designs differ significantly from industrial setups, complicating knowledge transfer. This work addresses these challenges by designing an iEFC with 1~cm^2 parallel electrodes to study the activity and stability of electrocatalysts simultaneously under industrially more relevant conditions. Simulation and experimental validation showed that the herein-designed iEFC enables a precise activity determination (Koutecký-Levich slope of >0. 95) over a wide potential range and minimal dilution of reaction products with a restricted volume flow. The stability determination was proven by online monitoring of the electrode dissolution with peak smearing comparable to reported values. This advanced iEFC was used to study the electrochemical conditioning of Ni- (Fe) -based electrodes to enhance the oxygen evolution reaction performance. Systematic parameter variation revealed consistent activation trends across the tested materials, promising universal activation guidelines and suggesting a similar activation mechanism. These activation trends are suggested to result primarily from surface oxidation and enlargement, with Fe dissolution from Ni-Fe-based electrodes or rather Fe incorporation into Ni-based electrodes being linearly linked with the (hydr) oxide formation. This increased understanding of conditioning parameters, activation, and surface changes offers a framework for tailoring any (pre-) catalyst’s conditioning to maximize performance or induce a certain surface change. Finally, the enduring activation efficacy during long-term electrolysis at 100~mA~cm^-2 and relevance to industrially more relevant conditions was demonstrated, i. e. 12~cm^2 electrodes, application of a separator, 30 wt% KOH, 80 °C, and higher loads. This makes the technology, including in-situ (re) activation of electrodes, more viable for large-scale applications, helping to reduce cell potential and optimize the anode manufacturing. Overall, this work stresses the importance of conditioning in enhancing the OER performance and demonstrates how to improve the catalysts' effectiveness by tailoring oxides.