Development of NiFeSx for Selective Oxygen Evolution Reaction (OER) in Alkaline Seawater: Mitigating Chlorine Evolution in Next-Gen Seawater Electrolysis Devices
Authors: Riaz Muhammad Sohail , Farràs Costa Pau , Kumar Praveen 
Published: December 2024

Efficient seawater electrolysis for hydrogen production faces challenges like active site poisoning, chloride oxidation, and anode corrosion, necessitating the development of effective oxygen evolution reaction (OER) electrocatalysts[1]. Strategies such as enhancing OER kinetics, mitigating chloride oxidation, bolstering corrosion resistance, and integrating multifunctionality into electrocatalysts are being pursued. Researchers explore internal and external cultivation methods to optimize electrocatalyst properties while understanding structural evolution and OER mechanisms remains crucial. Seawater electrolysis, tapping into Earth's abundant seawater resources, offers a scalable solution for green hydrogen production, especially when paired with renewable energy sources[2]. It holds promise for providing energy and water to offshore areas and mobile maritime systems, crucial for addressing energy and environmental challenges. In this study, we have fabricated a PGM (platinum group metal) free anode that shows promising performance in alkaline seawater. The material consists of nanoclusters of FeNiSx.

This study applied a polyol-assisted hydrothermal synthesis strategy to describe an advanced procedure for synthesising NiFeSx. Several physical and chemical characterisation tools are applied to investigate the anode electrode for alkaline seawater oxidation XRD, SEM, TEM and electrochemical characterisation. The outcomes of these characterisations were displayed as graphs. The catalysts reveal nanocluster morphologies. The figure below depicts the preliminary findings, illustrating the electrochemical performance and the physical characterisations. Figure 1 (a) and (b) depict the morphological evaluation by electron microscopy revealing the nanostructure-based clusters of the produced materials with the scanning and transmission electron microscopy, respectively. In. Polarisation curves of the oxygen evolution activity of the synthesised NiFeiSx electrocatalysts on Ni foam working electrodes, in a three-electrode configuration with Pt wire serving as the counter and Hg/HgO serving as the reference electrode in 0.1M KOH + 0.5 NaCl electrolyte. The best-performing catalysts obtained a high current exchange density close to 225 mAcm-2 shown in Figure 1(c). In addition, we are evaluating the efficacy of this high-performance anode electrocatalyst in a single-cell electrolyser and the best and most stable catalyst will be tested in stacks we are developing with our partners in the ANEMEL project.

Our research methodology encompasses a comprehensive array of ex-situ and in-situ characterization techniques to delve into the intricacies of seawater electrolysis for hydrogen production. We will utilize impedance spectroscopy to dissect electrochemical behaviour, including resistance, capacitance, and charge transfer resistance. Additionally, chronopotentiometry/chronoamperometry will assess the catalyst's long-term stability, while real-time examination of catalyst crystal structure during OER will be facilitated by Powder X-ray diffraction (XRD). Surface chemistry and elemental composition analysis will be conducted using X-ray photoelectron spectroscopy (XPS), while in-situ Raman spectroscopy will offer insights into electronic structure changes during the reaction, shedding light on the OER mechanism. Furthermore, FTIR spectroscopy will unveil reaction intermediates and mechanisms, providing a detailed understanding of the reaction pathway. Post-mortem catalyst analysis post-electrochemical testing will evaluate degradation, ultimately aiding in optimizing catalyst design for long-term stability and high-performance OER.

Acknowledgements

The authors acknowledge the ANEMEL Project funded by the Horizon Europe (European Innovation Council) Grant agreement 101071111.

Figure 1