Enhancing the Performances of P3HT:PCBM–MoS₃‑Based H₂‑Evolving Photocathodes with Interfacial Layers

Organic semiconductors have great potential for producing hydrogen in a durable and economically viable manner because they rely on readily available materials and can be solution-processed over large areas. With the objective of building efficient hybrid organic–inorganic photoelectrochemical cells, we combined a noble-metal-free and solution-processable catalyst for proton reduction, MoS₃, and a poly­(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction (BHJ). Different interfacial layers were investigated to improve the charge transfer between P3HT:PCBM and MoS₃. Metallic Al/Ti interfacial layers led to an increase of the photocurrent by up to 8 mA cm^–2 at reversible hydrogen electrode (RHE) potential with a 0.6 V anodic shift of the H₂ evolution reaction onset potential, a value close to the open-circuit potential of the P3HT:PCBM solar cell. A 50-nm-thick C₆₀ layer also works as an interfacial layer, with a current density reaching 1 mA cm^–2 at the RHE potential. Moreover, two recently highlighted figures-of-merit, measuring the ratio of power saved, Φ_saved,ideal and Φ_saved,NPAC, were evaluated and discussed to compare the performances of various photocathodes assessed in a three-electrode configuration. Φ_saved,ideal and Φ_saved,NPAC use the RHE and a nonphotoactive electrode with an identical catalyst as the dark electrode, respectively. They provide different information especially for differentiation of the roles of the photogenerating layer and catalyst. The best results were obtained with the Al/Ti metallic interlayer, with Φ_saved,ideal and Φ_saved,NPAC reaching 0.64% and 2.05%, respectively

Carbon Nanotube-Templated Synthesis of Covalent Porphyrin Network for Oxygen Reduction Reaction

The development of innovative techniques for the functionalization of carbon nanotubes that preserve their exceptional quality, while robustly enriching their properties, is a central issue for their integration in applications. In this work, we describe the formation of a covalent network of porphyrins around MWNT surfaces. The approach is based on the adsorption of cobalt­(II) <i>meso</i>-tetraethynylporphyrins on the nanotube sidewalls followed by the dimerization of the triple bonds via Hay-coupling; during the reaction, the nanotube acts as a template for the formation of the polymeric layer. The material shows an increased stability resulting from the cooperative effect of the multiple π-stacking interactions between the porphyrins and the nanotube and by the covalent links between the porphyrins. The nanotube hybrids were fully characterized and tested as the supported catalyst for the oxygen reduction reaction (ORR) in a series of electrochemical measurements under acidic conditions. Compared to similar systems in which monomeric porphyrins are simply physisorbed, MWNT–CoP hybrids showed a higher ORR activity associated with a number of exchanged electrons close to four, corresponding to the complete reduction of oxygen into water