Hierarchical micro-nano 3D structures of metal selenides on 2D NiCo–MXene nanosheets as a dual-layer electrocatalyst for effective seawater electrolysis and hydrazine degradation

Abstract

Seawater as an abundant and low-cost feedstock electrolyte is an outstanding candidate for electrolysis of water and producing significant gases such as hydrogen and oxygen during hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Seawater has a complex mixture including various ions and contaminations (e.g., hydrazine in the vicinity of industrial zones) that can interfere with a water electrolysis process. Thus, designing an effective electrocatalyst to facilitate seawater electrolysis and also transforming the hydrazine-damaging contamination into safer substances during the hydrazine oxidation reaction (HzOR) is a key factor. Herein, a two-layer electrocatalyst consisting of Viburnum flower-like three-phase 3D metal selenide structures decorated on the surface of the 2D NiCo–MXene (MS@NCT) nanocomposite is prepared using a fast two-step electrochemical procedure, which delivers remarkable trifunctional electrocatalytic activity for HER, OER, and HzOR reactions. The well-designed architecture of the MS@NCT electrocatalyst catalyzes the HER and OER processes at low overpotentials of 52 and 170 mV at a rate of −10 and 10 mA cm⁻² in alkaline electrolyte (1.0 M KOH), respectively. This nanocomposite as cathode and anode electrodes demands only a cell voltage of 1.47 V to afford a current density of 10 mA cm⁻² in the same electrolyte during overall water splitting (OWS). The investigation of the electrocatalytic activity of prepared electrocatalyst in alkaline seawater demonstrates the close overpotential for HER (52 mV at current density of −10 mA cm⁻²), OER (190 mV at current density of 10 mA cm⁻²), and OWS cell voltage (1.48 V at current density of 10 mA cm⁻²) compared to 1.0 M KOH. The hydrazine-assisted hydrogen production ability of MS@NCT with low voltage of 87 mV at low current density of 10 mA cm⁻² and 266 mV at high current density of 100 mA cm⁻² in alkaline seawater containing 0.5 M hydrazine proves the excellent efficiency of hierarchical multiphase electrocatalyst. DFT studies reveal FeSe@NiCo–MXene (FeSe@NCT) as a synergistic electrocatalyst, where interfacial charge redistribution and d-band modulation enhance conductivity and balance adsorption-desorption energetics. MXene weakens H∗ binding on NiCo and FeSe besides optimizing N₂ release, boosting HER and HzOR efficiency. They underscore interfacial electronic engineering for designing multifunctional catalysts.