A Tautomeric Carbon Nitride Structure for Photocatalytic Overall Water Splitting.

Constructing type-II heterojunctions is a prevalent strategy for enhancing the photocatalytic performance of polymeric carbon nitride (PCN). However, conventional PCN-based type-II heterojunctions are often limited by incoherent interfacial contacts, high charge-transfer resistance, and poorly aligned energy levels with large band offsets, all of which impede interfacial charge transfer and degrade the redox capability of photocarriers. In this study, we report a pseudo-resonance transformation strategy to selectively convert melon-type carbon nitride (MCN) into a topologically analogous yet electronically distinct conjugated derivative (C─MCN). This process constructs a unique MCN/C─MCN tautomeric heterojunction​ featuring a chemically bonded, coherent, and dangling-bond-free interface. Carrier dynamics analysis reveals that this structural continuum significantly lowers the energy barrier for exciton dissociation while facilitating efficient interfacial charge transfer. As a result, the obtained tautomeric heterojunction exhibits outstanding photocatalytic overall water splitting performance, achieving a hydrogen evolution rate 2.3 and 2.6 times higher than that of pristine MCN and standalone C─MCN, respectively. This work establishes a new paradigm for fabricating dangling-bond-free polymeric heterojunctions, providing an efficient pathway toward solar-fuel production.