Electrochemical Oxidation of Perfluorooctanoic Acid Using Thin Film Electrocatalysts Deposited on Reactive Electrochemical Membranes

Foam fractionation or use of ion exchange resins are effective methods to treat per- and polyfluoroalkyl substances (PFAS)-contaminated groundwater but these methods produce concentrated PFAS waste. Electrochemical oxidation of PFAS using Ti 4 O 7 reactive electrochemical membranes (REMs) have been demonstrated to effectively oxidize PFAS in some matrices and a potential method for mineralizing concentrated PFAS waste. In this work, we focused on synthesis of electrocatalyst using atomic layer deposition (ALD) on REMs to further enhance reaction rates of PFOA oxidation. First, thin films of ALD SnO 2 , Bi 2 O 3 , and Pd were deposited on REMs. For each ALD process, reactor temperature, precursor timing, and number of cycles were optimized for the porous, high aspect ratio (~5000) REMs. The synthesized electrocatalytic REMs were characterized using X-ray photoelectron spectroscopy (XPS) to evaluate the composition and oxidation states of the electrocatalyst. Moreover, top surface and cross-sections of the REMs were mapped using scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). The synthesized REMs were then tested for electrochemical oxidation of ~41 mg L -1 perfluorooctanoic acid (PFOA) in a flow-through reactor at a constant potential and flux to screen the effectiveness of the electrocatalysts and understand electrocatalyst dynamics during PFOA oxidation. The permeate collected from oxidation experiments were analyzed for long- and short-chain PFAS using liquid chromatography tandem mass spectroscopy and fluoride production using ion chromatography. Short-chain PFAS (C 2 , C 3 , C 4 , C 5 , C 6 , C 7 ) were detected with 10-25% yield, along with the formation of fluoride with 60-80% yield. Moreover, the samples were analyzed using inductively coupled plasma mass spectroscopy for assessing leached electrocatalyst under anodic conditions. Lastly, Al 2 O 3 and TiO 2 were deposited on the REMs to suppress the oxygen evolution reaction (OER) which is a side reaction under anodic conditions. Linear sweep voltammetry experiments were conducted using Al 2 O 3 and TiO 2 deposited REM to choose the best material for suppressing OER. The chosen material was deposited on the synthesized electrocatalytic REMs and tested for electrochemical oxidation of PFOA.