Molecular Photoelectrodes with Enhanced Photogenerated Charge Transport for Efficient Solar Hydrogen Evolution

Photoelectrocatalytic cells for seawater splitting have shown promise toward large-scale deployment; however, challenges remain in operation performances, which outline clear research needs to scale up photoelectrodes with small loss of efficiency. Here, we report an approach for scalable and robust solar H2 evolution by enhancing photogenerated charge transport in a H2-evolving molecular photoelectrode. The photoelectrode is based on p-type conjugated polymers that are homogeneously distributed in a polycarbazole network. With a self-assembled NiS2 catalyst, the photoelectrode under solar irradiation (100 mW cm-2, AM 1.5 G) is capable of evolving H2 from seawater at an external quantum efficiency (EQE) of 34.4% under an applied bias of -0.06 V vs RHE. When scaling up from 1 cm2 to 25 cm2, the photoelectrode generates photocurrents stabilized at 0.4 A and maintains the high EQE at an efficiency loss of less than 1%. Investigation of the photogenerated charge-transport dynamics reveals that the kinetic basis for scaling up lies in the desirable hole diffusion length that far exceeds the spacing between adjacent conjugated-polymer chains due to interchain π-π interactions.