Electrolysis of Seawater: An Effective Path to Sustainable Hydrogen Production with Sulfur-Doped NiFe LDH/MXene@NF Electrodes

Electrolysis of seawater is currently a promising technology for efficient green hydrogen production and solving the energy crisis. Urea oxidation reaction (UOR) has a low thermodynamic onset potential, which is an effective reaction to replace the oxygen evolution reaction (OER) in overall seawater splitting and avoid toxic hypochlorite generation. In this paper, we report sulfur-doped NiFe LDH with ultrathin nanoflower morphology on the surface of three-dimensional nickel foam (NF) loaded with Ti3C2Tx MXene by the two-step electrodeposition method (S-NiFe LDH/MXene@NF). The catalytic performance of electrolytic seawater is boosted by the synergistic effect of the abundant interface between Ti3C2Tx MXene and sulfur-doped NiFe LDH, which promotes electron transfer. S-NiFe LDH/MXene@NF exhibited electrocatalytic performance values of 1.578 and 1.437 V (vs RHE) for OER and UOR at 500 mA cm–2, respectively, and an overpotential of 336 mV for the hydrogen evolution reaction (HER) at 500 mA cm–2 in an alkaline seawater electrolyte. As a bifunctional electrode, it can achieve a current density of 500 mA cm–2 at 2.027 V with great stability. The in situ Raman detection of surface recombination of the S-NiFe LDH/MXene@NF electrode in the UOR demonstrates that Ti3C2Tx MXene accelerates the formation of the active species NiOOH on the electrode surface and facilitates the lattice disturbance of NiOOH. This helps to increase the catalytic activity of urea-assisted overall seawater splitting.