Bifunctionality behavior of phase controlled nickel selenides in alkaline water electrolysis application

•A well-controlled phase growth strategy to prepare nickel selenides series (NSNF).•NSNF exhibits comparable bifunctionality with the benchmark electrocatalyst.•NSNF delivers electrolysis stability test at a high current density condition. Nickel selenides have grasped extensive attention in the field of electrocatalysts for the energy -storage and -conversion applications due to their diverse stoichiometry phases being beneficial for designing and tailoring a unique chemical state. The comprehensive electrocatalytic understanding of nickel selenides possessing a scenario of more than one phase requires special attention for exploiting novel bifunctional electrocatalytic activity. In this report, we propose and develop two series of in-situ grown nickel selenide phases, NiSe2 and Ni0.95Se, supported on nickel foam (NSNF) as a bifunctional electrocatalyst for alkaline water electrolysis applications. The NSNF with a well-controlled uniform particle growth orientation provides a favorable active catalytic surface to deliver an exceptional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a 1 M of KOH electrolyte solution. The half-cell performance of the optimized NSNF electrode has been demonstrated to possess the following characteristics: In the HER evaluation, the achieved overpotential values of 175, 276, and 338 mV for 10, 50, and 200 mAcm−2, respectively; In the OER evaluation, the observed overpotential value of 325 mV at 50 mA cm−2 which outperformed the state-of-the-art IrO2 catalyst. Moreover, the alkaline water electrolysis cell demonstration using the optimized NSNF electrocatalyst as a bifunctional electrode exhibits an energy efficiency of 79% as well as a steady alkaline water-splitting process of 17 h at a current density of 50 mAcm−2. The insightful understanding of the bifunctional NSNF electrocatalysts asserts their potential use in the alkaline water electrolyzer applications. [Display omitted]