Phase-Tuned MoS 2 and Its Hybridization with Perovskite Oxide as Bifunctional Catalyst: A Rationale for Highly Stable and Efficient Water Splitting.

The efficient realization of bifunctional catalysts has immense opportunities in energy conversion technologies such as water splitting. Transition metal dichalcogenides (TMDs) are considered excellent hydrogen evolution catalysts owing to their hierarchical atomic-scale layered structure and feasible phase transition. On the other hand, for efficient oxygen evolution, perovskite oxides offer the best performance based on their rational design and flexible compositional structure. A unique way to achieve an efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a single-cell configuration is through the hybridization of TMDs with perovskite oxides to form a bifunctional electrocatalyst. Here, we report a simple yet effective strategy to inherently tune the intrinsic properties of a TMD based on MoS 2 and its hybridization with LaCoO 3 perovskite oxide to deliver enhanced electrocatalytic activity for both the HER and OER. Detailed Raman and XPS measurements highlighted a clear phase transformation of MoS 2 from a semiconducting to metallic phase by effectively tailoring the precursor compositions. Based on this, the morphological features yielded an interesting spherical flower-shaped nanostructure with vertically aligned petals of MoS 2 with increased surface-active edge sites suitable for the HER. Subsequent hybridization of nanostructured MoS 2 with LaCoO 3 provides a bifunctional catalytic system with an increased BET surface area of 33.4 m 2 /g for an overall improvement in water splitting with a low onset potential (HER: 242 mV and OER: 1.6 V @10 mA cm -2 ) and Tafel slope (HER: 78 mV dec -1 ; OER: 62.5 mV dec -1 ). Additionally, the bifunctional catalyst system exhibits long-term stability of up to ∼400 h under continuous operation at a high current density of 50 mA cm -2 . These findings will pave the way for developing cost-effective and less complex bifunctional catalysts by simply and inherently tuning the influential material properties for full-cell electrochemical water splitting.