Photocatalytic Hydrogen Evolution From Self-Assembled Stacks of Pd-TCPP and Pt-TCPP

The present work demonstrates that surfactant-free precipitation of Pd- and Pt-TCPP in MeOH/H₂O yields well-defined supramolecular architectures (µm-long nanorods) whose photocatalytic function tracks their metal-dependent photophysics and stacking. Among all tested M-TCPPs (M = Pd, Pt, Zn, Au, and Co), only Pd-TCPP and Pt-TCPP assemble to nanorods that are intrinsically active for H₂ evolution without any Pt cocatalyst, with Pd-TCPP outperforming Pt-TCPP robustly across the optimal aggregation window (pH ≈ 4-5). In fact, the cocatalyst-free Pd-TCPP nanorods surpass many other state-of-the-art porphyrin platforms, including Zn-TCPP assemblies operated with high-loaded Pt cocatalysts, as well as porphyrinic metal-organic frameworks (MOFs). The self-assemblies display J-type π-π stacking stabilized by carboxylate hydrogen bonding, producing broadened, red-shifted light absorption and efficient charge transport. Correlating XRD analysis, spectroscopy, and electrochemistry reveals that compared to Pt-TCPP, Pd-TCPP nanorods exhibit tighter π-π stacking, extended triplet-state lifetime, and lower charge-transfer resistance, consistent with more efficient charge separation and faster interfacial electron transfer. Importantly, the approach taken in this work allows for one-pot, surfactant-free, co-catalyst-free operation of Pd-TCPP nanorods that not only is of low synthetic complexity but also avoids surfactant residues while delivering a high and stable photocatalytic H₂ production activity under visible illumination.