Establishing a water-to-energy platform via dual-functional photocatalytic and photoelectrocatalytic systems: A comparative and perspective review

Light-driven photocatalytic (PC) and photoelectrocatalytic (PEC) systems are vital technologies being extensively explored for wastewater treatment and energy production. Although the photo(electro)catalytic applications in both the energy production and wastewater remediation function on the similar principle of photo-induced charge transfer, most preceding research has been focused on either the energy recovery or wastewater treatment as these two applications demand distinct reaction parameters and catalyst properties. The present review reveals the scientific progress in dual-functional PC and PEC processes that enable simultaneous energy recovery (e.g., H2 generation) with wastewater treatment (e.g., degradation of organic pollutants). The key concept in the dual-functional photo(electro)catalytic system is to use both the electron reduction power for recovering H2 from wastewater and hole oxidation power for degrading pollutants in wastewater simultaneously. Herein, a detailed and comprehensive overview of the advancement in various PC and PEC processes with dual-functional purpose is discussed, highlighting the advantages and disadvantages of different systems and performance comparison based on diverse metrics tools. Although in its infancy, this dual-functional technology has gained scientific interest over the past few years; this is expected, as this approach can overcome multiple major environmental challenges, such as water scarcity, global warming, and pollution. The review should offer current limitations and prospects for developing next-generation solar-driven dual-functional techniques based on the water-energy nexus.