MXene-Integrated Ni–Hf Nanoflowers for Efficient Water Splitting in Alkaline Wastewater: Experimental and DFT Insights

Alkaline water electrolysis (AWE) is a promising technology for producing green hydrogen. Unfortunately, the requirements for purified water, costs, and current limitations restrict its application. We proposed solutions to these barriers by employing wastewater effluents and an efficient MXene-based model electrocatalyst (NiHf-LDH/MXene/NF). In a two-electrode cell configuration, it requires 1.89, 1.92, 1.95, and 1.98 V for deionized water (DI), tertiary effluent (TE), secondary effluent (SE) from an external membrane bioreactor (eMBR), and the activated sludge process (ASP) to attain 1000 mA/cm2, outperforming benchmark electrocatalysts (Pt/C∥IrO2). Durability was evaluated at 650 mA/cm2 for 200 h in wastewater effluent, with a 0.603 mV/h drop. The system’s energy efficiency was 71.7 and 60.5% (based on the lower heating value (LHV)) at 100 and 1000 mA/cm2, respectively. Moreover, pollutant levels decreased: chemical oxygen demand (COD) (47.2%), total nitrogen (TN) (49.7%), turbidity (53.8%), and total dissolved solids (TDS) (5.7%). Density functional theory (DFT) indicates that the model electrocatalyst features an excellent adsorption energy (0.51 eV) for water molecules, which favors electrochemical reactions.