Supramolecular interaction of molecular catalyst on a polymeric carbon nitride photoanode enhances photoelectrochemical activity and stability at neutral pH

Abstract

Polymeric carbon nitride (CN) emerged as an alternative, metal-free photoanode material in water-splitting photoelectrochemical cells (PEC). However, the performance of CN photoanodes is limited due to the slow charge separation and water oxidation kinetics due to poor interaction with water oxidation catalysts (WOCs). Moreover, operation under benign, neutral pH conditions is rarely reported. Here, we designed a porous CN photoanode connected to a highly active molecular Ru-based WOC, which also acts as an additional photo-absorber. We show that the strong interaction between the -system of the heptazine units within the CN to the CH groups of the WOC’s equatorial ligand enables a strong connection between them and an efficient electronic communication path. The optimized photoanode exhibits a photocurrent density of 180 ± 10 μA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) with 89% Faradaic efficiency for oxygen evolution with turnover numbers (TONs) in the range of 3300 and turnover frequency (TOF) of 0.4 s–1, low onset potential, extended incident photon to current conversion, and good stability up to 5 h. This study may lead to the integration of molecular catalysts and polymeric organic absorbers using supramolecular interactions.