Metal waste-derived catalysts for electrocatalysis and photocatalysis applications: advances and perspectives

Converting hazardous metal waste (e.g., spent batteries, red mud, slag, and electroplating sludge) into functional materials has gained growing scientific interest due to its high environmental and economic benefits. While numerous reviews exist on biomass-derived catalysts, a comprehensive summary focusing on the rapid development of metal waste-derived electrocatalysts and photocatalysts for sustainability applications has been lacking. In this review, bridge this gap by comprehensively summarizing recent advances in this emerging field. Overall, the main strategies for developing electro/photocatalysts from metal waste are firstly summarized, including pyrolysis, wet-chemical, electrochemical, and microwave-assisted methods. Then, applications of metal waste-derived electrocatalysts in oxygen evolution, hydrogen production, nitrogen fixation, CO 2 conversion, and oxygen reduction are then analyzed. Subsequently, implementations of metal waste-derived photocatalysts in pollutant degradation, hydrogen production, and carbon dioxide/organic valorization are discussed. A special emphasis is put on highlighting catalysts' physicochemical property-performance correlation and outlining the efficient catalyst design strategies. Finally, key challenges and perspectives on the development of high-performance metal waste-derived catalysts for future sustainability applications are suggested, with a focus on the unique issues of stability, scalability, and sustainability assessment for these systems. This review aims to stimulate further research into the valorization of hazardous metal wastes for a circular economy.