Hierarchical Thiospinel NiCo2S4/Polyaniline Hybrid Nanostructures as a Bifunctional Electrocatalyst for Highly Efficient and Durable Overall Water Splitting

The development of a nonprecious, stable, and highly effective electrocatalyst for decomposition of water into oxygen and hydrogen is vitally important for sustainable energy conversion, but it still remains challenging to replace the noble metal electrocatalysts with more economically viable alternatives. Herein, a polyaniline (PANI) decorated hierarchical nickel cobalt thiospinel (NiCo2S4) hybrid catalyst (NCS‐P) has been developed that shows enhanced dual catalytic activity for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) compared to pristine NiCo2S4 (NCS). Benefiting from the conductive PANI coating, the hierarchical NCS‐P nanostructure exhibits outstanding electrocatalytic activity in alkaline solution with low overpotentials of 273 ± 3 and 77 ± 4 mV at 10 mA cm−2 and low Tafel slopes of 42.2 and 68.5 mV dec−1 for OER and HER, respectively, which are better than those of the benchmark noble‐metal‐based RuO2 and Pt/C. A polyaniline decorated thiospinel NiCo2S4 hybrid catalyst (NCS‐P) with high catalytic performance in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in basic medium is developed. The NCS‐P exhibits low overpotentials of 273 and 77 mV to achieve a current density of 10 mA cm−2 with low Tafel slope values for OER and HER, respectively, which are better than that of the benchmark noble‐metal‐based RuO2 catalyst and comparable to that of the commercial Pt/C.