Construction of K+ Ion Gradient in Crystalline Carbon Nitride to Accelerate Exciton Dissociation and Charge Separation for Visible Light H2 Production

The sluggish exciton dissociation and charge transfer and separation due to weak driving force still restrict the further improvement of photocatalytic performance in crystalline carbon nitride (CCN). Here, a series of heptazine-based K+-implanted CCNs (KCCNs) were successfully prepared, while the K+ ion concentration was gradiently inserted by controlling its diffusion from the surface to the bulk in carbon nitride (CN). The built-in electric field (BIEF) induced by the K+ ion concentration gradient and cyano groups has powerful driving force to promote the dissociation of excitons into electrons and holes and accelerate the separation of photogenerated carriers and their transport from the bulk to the surface. Consequently, the KCCN with an optimized BIEF has increased 34 times compared with the original CN for visible light H2 evolution. Our proposed strategy to induce BIEF by constructing concentration gradients through a thermodynamically feasible diffusion-controlled solid-state reaction can be adopted to design other photocatalytic systems.