Unified Catalytic Performance of Assimilated Bimetallic Sulfide onto Niobium Carbide MXene for Overall Water Splitting

Abstract The move from carbon fuels to renewable energy is accelerating the demand for efficient, affordable electrocatalysts. MXenes are rapidly budding as promising candidates for advanced energy carrier and storage systems. Ti‐based MXenes have been widely studied; however, their conductivity is relatively low compared to niobium‐based MXenes. In this work, the etching process is optimized to successfully remove Al from the Nb MAX phase, thereby developing a well‐exfoliated Nb‐MXene (NbX). Furthermore, to enhance the overall electrochemical performance, a novel catalyst is introduced by depositing nickel‐cobalt sulfide (NCS) onto NbX (NCS@NbX) to improve its activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The resulting catalyst achieves impressive overpotentials of 115 and 130 mV in 0.5 m H ₂ SO ₄ and 1 m KOH for HER and OER, respectively, nearly three times lower than the values observed for pristine NbX. Electrochemical testing further reveals low Tafel slopes of 93 and 98 mV dec⁻¹ for HER and OER, respectively. The catalyst also exhibits remarkable stability analyzed with the help of chronoamperometry testing, maintaining performance for over 40 h in acidic and 20 h in basic conditions, highlighting its robustness.