Bifunctional Water Splitting Photoelectrocatalysts Using Flexible Organometallic Complex and Nanographene Multilayer Thin Films

In comparison with conventional inorganic photocatalysts, organic photoactive materials are promising photocatalysts owing to their high extinction coefficient and chemical tunability. However, their limited photocatalytic activity, induced by a low relative permittivity with high recombination energy, poses significant challenges. Herein, a highly efficient bifunctional photocatalytic hybrid multilayer electrode is designed by a versatile layer-by-layer (LbL) assembly of nanoscale graphene oxide (nGO) and a ruthenium-terpyridine coordination complex (TPY2Ru). We exploited a synergistic effect between two active components, namely, the generation of photoinduced excitons by TPY2Ru and the facilitation of electron transfer by reducing the recombination rate of the generated electrons by nGO in hybrid electrodes. This photocatalytic electrode exhibits bifunctional activities for water splitting in neutral condition with the highest photoanodic current density of 4.28 μA/cm2 at 1.23 V versus a reversible hydrogen electrode (RHE) and a photocathodic current density of 28.42 μA/cm2 at 0 V versus RHE. Furthermore, the unique combination of hybrid materials enables the development of flexible photocatalytic electrodes with remarkable current density retention after a 1000-cycle durability test. Because of the highly tunable properties of the LbL-assembled multilayer electrodes, we anticipate that this strategy can offer insights into the nanoscale-architecture-controlled engineering of efficient photoelectrodes for future solar-fuel energy devices.