The charge transport double-channel structure facilitating Fe5Ni4S8/Ni3S2 nanoarray for efficient and stable overall water splitting

Abstract

Overall water splitting technology is critical for the future of a clean and sustainable hydrogen energy infrastructure. Ni3S2 (NS) is considered a good performing oxygen evolution reaction (OER) catalyst, but exhibits unsatisfactory hydrogen evolution reaction (HER) activity. In this study, Fe5Ni4S8 (FNS) material was incorporated into an NS nanoarray, generating a low-cost, efficient, and stable bifunctional FNS/NS heterostructure for electrolyzed water catalysts. The hydrophilicity of pretreated FNS was quite high, whereas the stepped rod-shaped NS structure had a large number of radial active sites. Additionally, the high-conductivity of FNS and nickel foam (NF) provided a double-channel structure for rapid internal charge transfer. The interconnecting a network of FNS, rod-shaped NS nanoarray, and NF substrate enabled one to accomplish a synergistic effect of enhanced kinetics and activity of OER, HER, and overall water splitting. To achieve a current density of 10 mA cm−2 in 1.0 M KOH solution, only overpotentials of 248 and 94 mV were required. Moreover, the voltage of the constructed FNS/NS||FNS/NS double-electrode battery system was only 1.64 V@10 mA cm−2, but the battery could have run for at least 120 h at an industrial current density of 500 mA cm−2. Therefore, this study offers a rational design of heterostructures as bifunctional electrocatalysts for overall water splitting.