Bifunctional Noble Metal-free Ternary Chalcogenide Electrocatalysts for Overall Water Splitting

TL;DR

This study introduces a new family of noble metal-free ternary chalcogenide catalysts, LaMS3, demonstrating high activity, stability, and bifunctionality for water splitting, advancing sustainable hydrogen production technology.

Contribution

The paper reports the synthesis and characterization of LaMS3 compounds, showing their superior bifunctional catalytic activity for water splitting compared to oxides, with detailed surface and bulk chemical analysis.

Findings

LaNiS3 exhibits the highest activity for HER and OER.

LaMS3 compounds show long-term stability over 18 hours.

These materials outperform ternary oxides in activity and Tafel slopes.

Abstract

Hydrogen has been identified as a clean, zero carbon, sustainable, and promising energy source for the future, and electrochemical water splitting for hydrogen production is an emission-free, efficient energy conversion technology. A major limitation of this approach is the unavailability of efficient, abundant, inexpensive catalysts, which prompts the need for new catalytic materials. Here, we report the synthesis and electrocatalytic properties of a novel transition metal-based ternary chalcogenide family, LaMS$_3$ (M = Mn, Fe, Co, Ni). Powder X-ray diffraction confirms the phase purity of these materials, while composition analysis using energy dispersive spectroscopy (EDS) confirms the presence of the stoichiometric ratio of elements in these compounds. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to study the chemical states on the surface and in bulk, respectively. These materials exhibit bifunctional catalytic activity towards the two half-reactions of the water-splitting process, with LaNiS$_3$ being the most active material for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The LaMS$_3$ compounds show long-term stability with negligible change in the overpotential at a constant current density of 10 mA cm$^{-2}$ over 18 hours of measurements. As compared to the corresponding ternary oxides, the LaMS$_3$ materials exhibit higher activity and significantly lower Tafel slopes. The ability to catalyze both half-reactions of water electrolysis makes these materials promising candidates for bifunctional catalysts and presents a new avenue to search for high-efficiency electrocatalysts for water splitting.