Photocatalytic membrane reactors as Photo-AOP platforms integrated with CO2-to-fuels modules: A paired photoelectrocatalysis perspective.

Photocatalytic membrane reactors (PMRs) have emerged as multifunctional platforms for advanced oxidation processes (AOPs), enabling simultaneous contaminant degradation and membrane filtration. However, their translation to large-scale applications remains limited by photon inefficiency, fouling and uncertain long-term stability. In parallel, electrochemical and photoelectrochemical carbon dioxide reduction (CO2RR) have advanced toward industrially relevant current densities, yet they remain constrained by the energy-intensive oxygen evolution reaction (OER) at the anode. This review systematically integrates recent technological advances in PMRs and CO2RR within a unified paired photoelectrocatalysis framework. A mechanistic coupling methodology is developed to analyze redox potential alignment, electron-flux distribution, pH decoupling, membrane-mediated ion transport and hydrodynamic synchronisation between anodic PMR oxidation and cathodic CO2 conversion. The analysis identifies PMRs as thermodynamically favourable alternatives to the OER, capable of reducing full-cell voltage while enabling simultaneous wastewater treatment and carbon valorization. Key limitations including radical-membrane interactions, fouling-induced photon attenuation, matrix scavenging and instability of anodic electron supply, are highlighted as critical barriers to integration. This review establishes a mechanistic and engineering roadmap for PMR-coupled CO2-to-fuel systems, positioning PMRs as dual-function anodic platforms for circular water-carbon technologies and low-emission environmental systems.