In Situ Generation and Stabilisation of Highly Active Electrodes for Cost-Effective Alkaline Water Electrolysis

Green hydrogen holds the potential to decarbonise sectors that are difficult to electrify directly, thereby supporting the transition to a sustainable energy system. Among the available technologies for producing green hydrogen, alkaline water electrolysis (AWE) is the most mature and is already deployed on an industrial scale. However, widespread adoption of green hydrogen remains hindered by high costs. One method for reducing the cost is to improve the efficiency of the electrolysis process, where the kinetic losses associated with the oxygen evolution reaction (OER) are a significant source of inefficiency.

The aim of this thesis is thus to identify and develop strategies to enhance the OER kinetics through the introduction of a suitable catalyst. Although extensive research has been devoted to understanding and developing OER catalysts, only limited progress has translated into practical improvements for industrial-scale electrolysers. Here, a key contributing factor is the discrepancy between academically centred experimental conditions and those encountered in commercial electrolyser stacks.

A central aspect often overlooked in the development of electrocatalysts is the impact of intermittent operation. In bipolar stack designs, shutdowns induce reverse currents and concomitant electrode discharging, imposing significant chemical and mechanical stress on the electrodes and catalytic coatings. In this thesis, the influence of reverse currents on the durability of bare, untreated nickel anodes was systematically investigated. Repeated redox cycling, including reverse currents under industrially relevant conditions (8 M KOH, 80°C), resulted in an anode mass loss corresponding to several hundred nanometers of nickel. The deterioration was found not to arise from the reduction event of the NiOOH-covered anode, but from the prolonged residence in the reduced Ni(OH)₂ state. Crucially, this deterioration was not detected during brief potential sweeps across the Ni²⁺/³⁺ transition, highlighting that standard stability assessment techniques, such as cyclic voltammetry, might not detect deterioration pathways observed in industrial electrolysers.

Building on these insights, the performance of a range of nickel-based anodes, including simple bare nickel, in situ-grown hydrous oxides, and state-of-the-art hydrothermally synthesised NiFe layered double hydroxide (LDH) catalysts, was evaluated under industrial conditions with intermittent operation. Across the studied materials, it was observed that the presence of iron in the electrolyte was a prerequisite for maintaining a high OER activity. While both the hydrous oxide-covered nickel anode and the NiFe-LDH catalyst degraded during repeated shutdown cycling, the catalytically active phase could be regenerated when dissolved iron was available in the electrolyte. After the experiment, including shutdown cycling, all electrodes exhibited comparable OER activity and electrochemical surface area, as assessed by impedance spectroscopy. Post-mortem analysis using X-ray photoelectron spectroscopy, high-resolution scanning electron microscopy, and Raman spectroscopy further revealed that the surface structures had converged towards a nearly identical (oxy)hydroxide phase. The porous diaphragm employed in AWE enables the migration of dissolved iron between the electrodes, resulting in its accumulation on the cathode. This work demonstrates that iron deposition deactivates a hydrogen evolution catalyst based on platinum-group metals (PGM), consequently offsetting the efficiency gains achieved at the anode. Stepwise addition of iron to the electrolyte indicated that a narrow concentration window might enable simultaneous efficient operation of both electrodes. However, modelling of stainless steel corrosion in a simulated industrial electrolyser shows that maintaining this optimal iron concentration is impractical. The development of a hydrogen evolution catalyst with greater tolerance to iron poisoning is, therefore, considered a more robust solution.

Ultimately, the findings presented in this thesis demonstrate that incorporating industrially relevant operating conditions into laboratory-scale testing improves the stability assessment of OER catalysts. Under these conditions, it is demonstrated that the chemical environment of the electrolyser governs the development of the active phase of nickel-based catalysts. These insights establish a more realistic foundation for designing durable and efficient catalysts for next-generation alkaline water electrolysers.