Stabilizing carbon nitride photoanodes for unassisted alcohol reforming coupled to CO2 reduction under concentrated sunlight

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 RHE) enabled over 20 hours of continuous operation. In situ spectroscopy and impedance analysis linked degradation at higher potential (>0.4 V vs RHE) to irreversible morphological changes and self-oxidation, exacerbated by conductivity loss. These insights enabled the unprecedented stabilization of carbon nitride photoelectrodes and paved the way for the development of the first 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 reduction for over 70 h. This work sets a new benchmark for carbon nitride stability and PEC deployment, highlighting the need to revisit testing protocols to unlock the full potential of emerging semiconductors.