Rational Construction of NiS2/CoTe Nanostructures as Bifunctional Electrocatalysts for Overall Water Splitting

Abstract Developing efficient, low-cost bifunctional electrocatalysts for overall water splitting is crucial for sustainable hydrogen production via water electrolysis. Herein, a NiS2/CoTe heterostructure with tunable compositional ratios was successfully synthesized via a facile hydrothermal method and systematically investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) applications. Structural characterization revealed that crystalline NiS2 nanoparticles were uniformly anchored on conductive CoTe nanosheets, forming a well-defined nanoscale heterointerface. Among the synthesized catalysts, the optimized NiS2/CoTe-90:10 heterostructure exhibited the highest catalytic activity, requiring overpotentials of only 168 and 363 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively. NiS2/CoTe-90:10 further exhibited superior long-term durability and high faradaic efficiencies of 98.3 ± 0.5% and 97.8 ± 0.3% for HER and OER, respectively. The catalyst achieved H2 and O2 production rates of 414.3 and 194.4 μmol/h, respectively, while achieving turnover frequency (TOF) of 6.16 × 10−2 s−1 for HER and 12.21 × 10−3 s−1 for OER, representing a twofold and 1.4-fold enhancement over pristine NiS2, respectively. This improved performance originates from the synergistic coupling between NiS2 and CoTe, accelerated interfacial charge transfer, and enlarged electrochemically active surface area. Moreover, a single-stack anion-exchange membrane alkaline electrolyzer using the NiS2/CoTe-90:10 achieved a cell voltage of 1.78 V at 10 mA/cm2. This work provides valuable insights into the nanoscale heterointerface engineering of transition-metal chalcogenides to rationally design next-generation bifunctional electrocatalysts for efficient water splitting.