Ni${}_x$B/Mo${}_{0.8}$B${}_3$ nanorods encapsulated by a boron-rich amorphous layer for universal pH water splitting at the ampere level

Heterostructured interfaces are crucial to electrocatalysts for water splitting. Herein, coral-like multiheterostructured Ni${}_x$B/Mo${}_{0.8}$B${}_3$ (NMB) nanorods encapsulated by a boron-rich amorphous layer are prepared for water splitting. Density-functional theory (DFT) calculations indicate that the NMB interface adjusts the d-band center and electronic structure of the molybdenum sites. Owing to the strong electronic coupling between Ni, Mo, and B at the heterojunction, large number of exposed catalytic active sites, as well as the special hydrophilic characteristics endowed by the surrounding amorphous layer, the NMB catalyst exhibits remarkable universal-pH hydrogen evolution reaction (HER) activity with low overpotentials (η) of 15, 26, and 83 mV to deliver 10 mA cm${}^{-2}$ in basic, acid, and neutral media, respectively, and outstanding oxygen evolution reaction (OER) characteristics in the basic medium with η${}_{10}$ and η${}_{500}$ of 170 and 420 mV, respectively. The unique self-supporting 3D hierarchical interconnected structure facilitates mass transport thus leading to high mechanical stability for 450 and 200 h in HER and OER at ≈1000 mA cm${}^{-2}$. More importantly, the NMB exhibits excellent performance toward overall-water electrolysis as a bifunctional catalyst with ultralow cell voltages of 1.45/1.56/1.85 V @ 10/100/1000 mA cm${}^{-2}$, demonstrating the large potential in industrial water splitting applications. (© 2024 Wiley-VCH GmbH)