Progress on catalytic electrodes and fuel cell systems for industrial wastewater treatment

Industrial wastewater containing dyes, antibiotics, heavy metal ions and other refractory organic pollutants has complicated components and poor biodegradability. Comparing to traditional bio-treatment processes, electrochemical technologies have significant advantage in treating such kinds of wastewater due to the electrochemically generated reactive species. Modifying the electrodes with catalytic components can enhance pollutant removal capacity in electro-catalytic (EC) or photo-electro-catalytic (PEC) integrated systems, but high energy consumption of electricity still restricts their implement. Self-biased fuel cells, including photocatalytic fuel cells (PFCs) and microbial fuel cells (MFCs), are more sustainable in industrial wastewater/pollutants treatment. Highly active catalytic electrodes are essential to promote pollutant removal and energy conservation. This article reviews the recent development of novel catalytic electrodes in preparation, optimization and sustainable application for industrial wastewater treatment. Technical advantages and optimization spaces of fuel-cell integrated systems (based on PFCs and MFCs) are introduced, and their challenges in large-scale application are pointed out. Catalytic electrodes have broader application fields than powder-form catalysts due to the easy-recyclability and the synergy of catalysis and electrochemistry. An ideal catalytic electrode should be conductive, highly (photo-)electro-active, physically and chemically stable, easy to prepare and low-cost. By optimizing the preparation/loading of novel catalytic materials (heterojunctions, single-atom catalysts etc.), various catalytic electrodes, in forms of self-standing (metal-based, carbon-based