Advanced and Scalable Polyol-Mediated Synthesis Route for Highly Active Ni Metal Sulfides (M = Fe, Mn, Cr, Mo) As Efficient Electrocatalysts for Sea/Saline Water Oxidation
Authors: Riaz Muhammad Sohail , Farràs Costa Pau 
Published: February 2024

Recent studies have made significant progress in addressing oxygen evolution (OER), a bottleneck reaction in water electrolysis, by utilizing innovative electrode materials and catalysts to enable low-grade and saline water splitting, thus offering promising prospects for advancing sustainable hydrogen production systems.1 This study applied a modified polyol-mediated strategy2 to describe an advanced procedure for synthesizing NiMSx where M = (Fe, Mn, Cr, Mo). Several physical and chemical characterization tools are applied to investigate the obtained saline/seawater oxidation electrocatalysts, including XRD, SEM, TEM, and electrochemical characterization. The outcomes of these characterizations were displayed as graphs. The catalysts reveal nanoclusters morphologies. The figure below depicts the preliminary findings, illustrating the electrochemical performance and the physical characterizations. Figure 1 (a) and (b) represent the polarisation curves of the oxygen evolution activity of the synthesized MNiSx electrocatalysts on Carbon cloth and Ni foam working electrodes, respectively, in a three-electrode configuration with Pt wire serving as the counter and Hg/HgO serving as the reference electrode in 1M KOH plus natural seawater from the Galway Bay Ireland. The catalysts obtained a high current exchange density of above and close to the 200 mAcm-2. Figure 1(c) displays the images of the catalyst-coated working electrodes prepared via dip coating, both Ni foam and carbon cloth, while Figures 1(d) and 1(e) reveal the nanostructure-based clusters of the produced materials with the scanning and transmission electron microscopy, respectively. In addition, we are evaluating the efficacy of this high-performance anode electrocatalyst in a single cell with a working electrode area of 3 cm2 for the oxygen evolution reaction (OER) and Pt/C as a cathode for hydrogen evolution reaction (HER). Our research project aims to develop highly efficient Oxygen Evolution Reaction (OER) catalysts.
We will employ various ex-situ and in-situ characterization techniques, including, Impedance spectroscopy, chronopotentiometry/chronoamperometry, Powder X-ray diffraction (XRD), Raman spectroscopy, and FTIR spectroscopy. Impedance spectroscopy determines the system's impedance as a function of frequency and offers insights into electrochemical behavior, such as resistance, capacitance, and charge transfer resistance. Chronopotentiometry/chronoamperometry will be applied to check the long-term stabilities of catalysts. X-ray diffraction (XRD) will examine the crystal structure of the stimuli in real-time during OER. X-ray photoelectron spectroscopy (XPS) will be applied to analyze the materials' surface chemistry and elemental composition by measuring the energies of emitted photoelectrons from X-ray irradiation. In-situ Raman spectroscopy will enable us to study changes in the catalysts' electronic structure and coordination environment during the reaction providing valuable insights into the underlying mechanism of OER. FTIR spectroscopy will reveal information about the response intermediates and mechanisms during OER. We can obtain a detailed understanding of the reaction pathway by monitoring the changes in the vibrational spectra of the reactants and products. Finally, post-mortem analysis of the catalysts will be performed after electrochemical testing to assess their degradation. Above all will help us optimize the catalysts' design for long-term stability and high-performance OER.

Acknowledgments

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

References

Tong, W.; Forster, M.; Dionigi, F.; Dresp, S.; Sadeghi Erami, R.; Strasser, P.; Cowan, A. J.; Farràs, P., Electrolysis of low-grade and saline surface water. Nature Energy
2020,
5 (5), 367-377.

Zhang, H.; Hyun, B.-R.; Wise, F. W.; Robinson, R. D., A generic method for rational scalable synthesis of monodisperse metal sulfide nanocrystals. Nano letters
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12 (11), 5856-5860.

Figure 1