Schiff Bases Complexes prepared from Polyethylene Terephthalate and Amine for Alkaline Water Electrolysis

Alkaline water electrolysis is considered a viable technology for large-scale hydrogen production due to its use of non-precious metal catalysts. This process involves two half-slow-rate electrochemical reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In contrast to non-precious metal electrocatalysts, typically employed for acid-media reactions to enhance slow electrochemical activities, precious metals like Ir/Ru compounds for OER and Pt for HER are used. However, relying on such relatively scarce and precious catalysts is not advisable, as it significantly inflates the cost of hydrogen production and hampers future industrial scalability. Consequently, there is a pressing need to develop high-performance non-precious metal alternatives.<br/>This study investigates metal Schiff base complexes derived from polyethylene terephthalate (PET) and various amines. PET materials have been used for packaging since the 1960s, with global consumption surpassing 24 million tons annually and continuing to rise. While PET's durability is advantageous, its downside is its slow biodegradation rate, taking up to 500 years to decompose in landfills when disposed of as waste. Unfortunately, many developing countries have low PET recycling rates.<br/>PET is a condensation polymer synthesized from terephthalic acid (BDC) and ethylene glycol (EG). The degradation of PET was achieved through a solvent-assisted glycolysis process using EG to obtain BDC. BDC contains carbonyl groups capable of reacting with amine compounds to form Schiff bases. These metal Schiff bases are formed when Schiff base ligands' azomethine groups (–RC=N–) coordinate with metal ions. The study meticulously screened amines' chemical composition and compound ratios to identify those exhibiting optimal electrochemical properties. Furthermore, the study delves into the mechanism and effects of these Schiff bases on OER/HER.<br/>Diverse Schiff bases were synthesized by combining terephthalic acid (TPA) with various amine compounds, including ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PTHA). In the context of alkaline water electrolysis, the two-electrode cell employing the unheated Fe_0.5Cu_0.5Mo_0.5-SB-TEPT @NF couple as both the anode and cathode exhibited higher levels of H₂ and O₂ production compared to the Pt/C and RuO₂ couple at 100 mA/cm².<br/>The study expects that metal Schiff bases will demonstrate outstanding electrolysis performance in alkaline water electrolysis, offering innovative applications for PET recycling and contributing to the resolution of the waste PET problem.