Stabilizing Carbon Nitride Photoanodes for Unassisted Alcohol Reforming Coupled to CO2 Reduction under Concentrated Sunlight

Abstract

Carbon nitride is a scalable and low-cost organic semiconductor with promise for use in photoelectrochemical (PEC) devices, but its poor stability limits its practical use. This study establishes the importance of light intensity and applied electrochemical potential on the stability of cyanamide-functionalized carbon nitride photoanodes used for waste-derived alcohol oxidation. Operating under concentrated sunlight (3 suns) and low bias (<0.2 V vs reversible hydrogen electrode, RHE) enabled over 20 h of continuous operation. In situ spectroscopy and impedance analysis linked carbon nitride degradation at higher potential (>0.4 V vs RHE) to irreversible morphological changes and self-oxidation, exacerbated by conductivity loss. These insights enabled the stabilization of carbon nitride photoelectrodes and paved the way for the development of a standalone PEC device with an integrated thermoelectric unit to convert heat into an additional internal bias-voltage, where carbon nitride efficiently drives alcohol oxidation coupled to CO2-to-CO conversion for over 70 h. This work sets a benchmark for carbon nitride stability and PEC deployment, and highlights the need to revisit PEC testing protocols to unlock the full potential of emerging semiconductors.