Anion-engineered thiospinels through sulfur-phosphorus exchange for enhanced water splitting and energy storage

Abstract

High-performance, low-cost electrocatalysts are critical for sustainable energy technologies, including water splitting and supercapacitors. Herein, we demonstrate a novel anion-engineering strategy to enhance the bifunctional activity of thiospinels via a controlled sulfur-phosphorus exchange. Initially, mixed-metal thiospinels, NiCo 2 S 4 and CuCo 2 S 4 , were synthesized from the thermal decomposition of their respective metal (Ni, Cu, Co) xanthate complexes. Subsequent heating of these materials in trioctylphosphine (TOP) resulted in a sulfur-phosphorus exchange, leading to the formation of anion-engineered metal phosphides, specifically NiCoP and Co 2 P. The formed Co 2 P retained some sulfur (with the presence of Cu sulfides), contrary to NiCoP. We show that these (S/P) mixed-anion compounds exhibit superior electrochemical performance compared to their parent thiospinels. The anion-engineered NiCoP demonstrated a significant improvement in energy storage, achieving a specific charge of 637.73 C/g at 1 A/g. Concurrently, the Co 2 P material, with its tailored anionic composition, showed outstanding water splitting activity, requiring only 167 mV to achieve a current density of 10 mA/cm 2 for the hydrogen evolution reaction. This anion substitution strategy also positively influenced reaction kinetics, long-term stability, and overall electrode durability. Our findings introduce a facile and effective anion-engineering approach for creating high-performance catalysts, highlighting the critical role of anionic composition in optimizing materials for advanced energy applications. • We demonstrate anion-engineering strategy to enhance the bifunctional activity of thiospinels. • NiCo 2 S 4 and CuCo 2 S 4 , were synthesized from decomposition of their metal xanthate complexes. • Heating of these materials in TOP resulted in a sulfur-phosphorus exchange. • This led to the formation of anion-engineered metal phosphides with residuel sulfur. • The (S/P) mixed-anion compounds exhibit superior electrochemical performance.