Bias-Free Photoelectrochemical Water Splitting Cells Constructed by Calixarene Dyes and Molecular Ru Catalysts via Pyridyl Anchoring Groups

Abstract

Two metal-free calix[4]­arene dyes with pyridyl anchoring groups (C4BTP and C4STP) and a comparative single-chain dye (M-BTP) for comparison have been synthesized and applied in dye-sensitized photoelectrochemical cells in corporation with a pyridyl anchor-based molecular water oxidation catalyst (RuPy). All the devices based on the three dyes can conduct overall water splitting reaction under visible light with low or zero bias. It is confirmed that the cone structure and multiple light-harvesting units of calixarene dyes bring superior durability and photoelectroconversion property compared with chain dyes M-BTP, and the introduction of alkalinous pyridyl anchoring groups improves the adsorption firmness on TiO2 in aqueous solution through the Ti–N bond. The optimized TiO2|C4BTP+RuPy photoanode gives the highest photocurrent density of over 800 μA cm–2, while the TiO2|C4STP+RuPy photoanode exhibits the best Faradaic efficiency of 64.9% for O2 evolution. To meet the needs of practical applications, the TiO2|C4BTP+RuPy photoanode is utilized in a two-electrode system with 0 V bias, giving a steady photocurrent density of 42 μA cm–2 in 3600 s and a Faradaic efficiency of 45.9% for O2 evolution. This study offers an inspiration for developing efficient and durable organic photosensitizers in photocatalytic water-splitting devices.

Highly Efficient and Stable Molecular-Based TiO2 Photoanodes for Photoelectrochemical Water Splitting Achieved by Pyridyl Anchoring Technique

“…In contrast, our “pyridyl anchoring technique” indeed enabled tight binding of molecular components over the TiO 2 surfaces based on the highly stable Ti–N (pyridyl) bonding even under visible light irradiation in fully aqueous media . By adopting our pyridyl anchoring technique, several other groups have reported on the molecular-based TiO 2 photoanodes showing an improved long-term stability. − Among them, some molecular-based photoanodes have been shown to preserve their photoelectrocatalytic activity over 1 h even under the aqueous operating conditions. , …”

KuQuinones: a ten years tale of the new pentacyclic quinoid compound

“…Metal-free organic sensitizers are emerging as a new alternative to metal complexes, such as ruthenium( ii ) polypyridine derivatives. 73 Porphyrins, 74–76 perylenediimide 77–79 derivatives, donor–π–acceptor molecules 80–85 and calixarenes 86 have been exploited with different WOCs, obtaining good to excellent photocurrent and faradaic efficiencies, in terms of oxygen production (Table 1, Fig. 12).…”

Photoelectrochemical Cells with a Pyridine-Anchored Bilayer Photoanode for Water Splitting

“…An issue of using these anchoring groups is that it is usually troublesome to incorporate these groups in synthesis and the resulting films suffer from poor stability in aqueous media. − In this context, we have recently designed a series of organic molecules with multiple terminal pyridine groups as anchors to link functional molecules to the surface of metal or metallic oxide. − This strategy was used to fabricate stable electrochromic films and photoanodes and photocathodes with excellent stability in aqueous media for the construction of DSPECs for H 2 production. In addition to our efforts, the pyridine anchoring strategy has been employed by others on the investigation of interfacial photocatalytic reactions in recent years. ,− …”