Tunability of Carbon Nitrides for Enhanced Photocatalytic Oxygen Evolution Reaction

This study presents a systematic theoretical and experimental investigation aimed at optimizing the photocatalytic oxygen evolution reaction (OER) performance of poly(heptazine imides) containing metal cations (PHI-Ms). Deploying advanced density functional theory (DFT) and time-dependent DFT calculations, time-resolved spectroscopy, and photocatalytic OER measurements, we established key design principles for enhancing the OER activity: (i) favoring Co and Fe cations in the +III oxidation state to improve light-harvesting and reduce the Gibbs free changes; (ii) minimizing the content of K+ co-cations, which negatively affect catalytic performance by increasing the desorption Gibbs free energy of O2 and promoting charge localization; (iii) avoiding high concentrations of metal cation to limit agglomeration and mitigate charge recombination; and (iv) exploring oxygen doping of the PHI layer by substituting N atoms located away from the metal active sites, thereby enhancing charge separation and promoting hole generation. These insights offer valuable design guidelines for the development of PHI-M systems with improved photocatalytic performance, advancing the potential of earth-abundant catalysts for practical water-splitting applications.