A suspension-mimicking hydrogel-based n-type polymer photocathode for solar-driven water splitting

Graphitic carbon nitride is a benchmark n-type polymer photocatalyst for hydrogen evolution from water in suspension systems, though it is extremely inefficient in photoelectrochemical (PEC) systems. Minimizing the considerable discrepancy between the two systems is challenging but necessary for applications. Efficient electron collection on the catalyst surface is key to carbon nitride’s photocatalytic hydrogen evolution performance in suspension systems, but it is rarely achieved in PEC films because of the electron transfer barrier from bulk to the surface. Here, we report a hydrogel-based PEC photocathode that inherits the intrinsic advantages of suspension systems, providing a suspension-like environment for carbon nitride hydrogen evolution. This promotes electron trapping at heteroatom-induced shallow surface trap states, mitigates space charge layer, and reduces charge migration distance in hydrogel-supported heteroatoms-doped carbon nitride nanosheets, enabling efficient electron collection on the surface, leading to 10-time improvement in photocathodic performance. This study provides proof of concept for mimicking suspension in photoelectrodes that can be applied to various powder-based photoelectrochemical cells.