Long-lasting BDD/Si3N4-TiN Electrodes for Sustainable Water Remediation

Boron-doped diamond (BDD) thin films have the potential to revolutionize water remediation through electrochemical oxidation, converting persistent pollutants into CO2 and water. However, a significant challenge in implementing BDDs on a large scale is the choice of substrate material. Electrode failure typically occurs due to BDD delamination from the substrate. We propose using a ceramic composite of silicon nitride (Si3N4) and titanium nitride (TiN) as a substrate to address this issue. This electroconductive composite combines Si3N4's high wear resistance, chemical stability, and high affinity for diamond film growth with the TiN's metal-like conductivity. In this work, BDD films were grown by Hot Filament Chemical Vapor Deposition (HF-CVD) over Si3N4-TiN substrates containing 30%vol. TiN. The resulting BDD/Si3N4-TiN electrodes were analyzed concerning their microstructure, diamond quality, conductivity, adhesion strength, service life, and electrochemical properties. Phenol was used as a model to test the electrode's ability to oxidize pollutants. We found that the BDD/Si3N4-TiN electrode could eliminate phenol entirely and up to 98.8% of the model solution's Chemical Oxygen Demand (COD) after 5 hours of direct anodic oxidation, with an Average Current Efficiency (ACE) of 14% and an energy consumption of 138 kWh kgCOD-1. Furthermore, the BDD/Si3N4-TiN electrode could withstand more than 2016 h of accelerated life test without film delamination. Overall, the results demonstrate that BDD/Si3N4-TiN electrodes are a potential long-lasting solution for large-scale water treatment by electrochemical advanced oxidation processes (EAOPs) in a sustainable manner, especially if combined with renewable energy sources.