Synergistic heterojunctions of CoSe2 and NiFe layed double hydroxide: bridging in situ phase evolution and charge redistribution as bifunctional catalysts for water splitting

Electrolytic hydrogen production is fundamentally constrained by the sluggish kinetics of both the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. To address this challenge, the development of efficient, durable, and economically viable bifunctional electrocatalysts is critical for advancing sustainable water splitting technologies. In this work, we present a rationally designed composite nanoflake heterostructure comprising CoSe₂ and NiFe layered double hydroxide (LDH) anchored on nickel foam (CoSe₂@NiFe-LDH/NF), synthesized via a facile two-step electrodeposition. This integrated architecture exhibits exceptional bifunctional catalytic activity for both HER and OER. In situ Raman spectroscopy analysis demonstrated that CoSe bond cleavage induces cobalt oxidation and selenium leaching, while the CoSe₂/NiFe-LDH interface orchestrates electron redistribution to drive NiFeOOH formation, synergistically enhancing OER activity through coupled electronic modulation and structural reconstruction dynamics. Structural characterization and theoretical calculations show that the charge redistribution at the heterojunction interface optimizes the adsorption energy of the reaction intermediates, thus improving the OER and HER performance. As a result, the optimized CoSe₂@NiFe-LDH/NF demonstrates a modest overpotential of 227 mV@50 mA cm⁻² for HER and 266 mV@100 mA cm⁻² for OER. Furthermore, the CoSe₂@NiFe-LDH/NF composite material employed in the overall water splitting cell demonstrates remarkable stability by maintaining a current density of 100 mA cm⁻² at an applied voltage of 1.75 V for an extended duration of 100 h. This study not only presents a simple and convenient strategy for synthesizing cost-effective and high-efficiency bifunctional electrocatalysts but also establishes novel pathways for advancing the performance of non-precious metal electrocatalysts.