In the pursuit of sustainable global development, mitigating carbon emissions and addressing plastic waste accumulation have emerged as critical challenges. Solar-powered systems offer a clean, cost-effective pathway to tackle these issues by enabling the conversion of CO₂ into fuels while simultaneously recycling plastic waste into high-value products, advancing waste reduction and circular economy objectives.

The PHOENIX project embodies this dual approach, focusing on the stepwise, solar-driven conversion of CO₂, beginning with its reduction to carbon monoxide (CO) and subsequent transformation into propanol. Concurrently, PET plastic waste is upcycled into glycolic acid, establishing a synergistic system that integrates renewable fuel production with plastic waste valorization.

To realize this vision, PHOENIX advances a tandem solar system that couples a photovoltaic-electrolyzer (PV-EC) unit with a photoelectrochemical (PEC) cell capable of generating over 2 V under sunlight to drive the targeted electrochemical transformations efficiently. The system is also being evaluated under concentrated light conditions to enhance solar flux utilization, increasing reaction rates and device productivity.

Recent developments within the Leitat team have significantly advanced the PEC component of the PHOENIX system through the design of stable, scalable photoanodes based on hematite (α-Fe₂O₃), addressing two key challenges in PEC technology: operational stability under realistic solar flux and scalable fabrication for device-relevant areas.

The Leitat team has developed Ti- and Ge-doped hematite thin films,[1] which exhibit improved electrical conductivity and enhanced charge separation, reducing recombination losses and increasing photocurrent densities under simulated and concentrated solar illumination. To further enhance performance, these doped photoanodes have been decorated with robust Ni-based and NiPt@C co-catalyst, which significantly lower the overpotential for the oxygen evolution reaction (OER) while ensuring chemical stability in alkaline media. Moreover, the system enables the ethylene glycol oxidation reaction (EGOR), a key step for valorizing PET-derived ethylene glycol into glycolic acid, contributing to plastic waste upcycling under solar-driven conditions within the PEC module.

To address scalability, low-temperature deposition techniques compatible with large-area substrates have been implemented, enabling the production of photoanodes with active areas exceeding 25 cm² while maintaining uniform semiconductor and catalytic properties. These scalable photoanodes have demonstrated stable operation under continuous illumination, maintaining high photocurrent densities necessary for practical PEC operation in PHOENIX.

By integrating these advanced photoanodes within the PEC module, PHOENIX is positioned to demonstrate the solar-driven production of propanol from CO₂ while enabling the valorization of PET waste into glycolic acid within a unified, circular process. The system will undergo lab-scale validation at Technology Readiness Level (TRL) 4, including a Life Cycle Assessment (LCA) to evaluate environmental impact and material recyclability.

By addressing both CO₂ reduction and plastic waste recycling through innovative photoelectrode technology, PHOENIX represents a high-risk, high-reward approach poised to drive significant breakthroughs in renewable energy and waste management technologies.