Molten Salt Modulation of Potassium–Nitrogen–Carbon for the Breaking Kinetics Bottleneck of Photocatalytic Overall Water Splitting and Environmental Impact Reduction

Sluggish interfacial water dissociation and the O₂ evolution reaction (OER) kinetics are the main obstacles that limit the photocatalytic overall water-splitting performance. A molten salt modulation of potassium-nitrogen-carbon is herein demonstrated as the formation of highly crystalline potassium-doped poly(triazine imide) (KPTI). The in situ X-ray diffraction patterns and theoretical calculation show that the KCl melt can significantly reduce the free energy for the polycondensation of triazine building blocks owing to the formation of a kinetically stable KPTI. Benefiting from the presence of potassium-carbon-nitrogen moiety, the catalyst not only weakens the excitonic confinement to improve the separation efficiency of photogenerated charge carriers but also enhances the stability of carbon sites by suppressing the undesired C═O formation. Moreover, KPTI accelerates water dissociation by forming interfacial K·H₂O clusters with an ordered structure, which supplies sufficient protons for the H₂ evolution reaction and lowers the energy barrier to enhance the kinetics of OER. Therefore, a stable photocatalytic overall water-splitting performance can be achieved over KPTI with a stoichiometric generation of products (H₂ and O₂). Life cycle assessment shows that a carbon-neutral scenario can be achieved on KPTI production in the near term with an increase in green power in the electricity grid.