Ni^II-Porphyrin Metallo-Supramolecular Gel Electrodes for Solar-Driven Water Oxidation Coupled With Dark CO₂ Reduction

Developing a single material capable of driving simultaneous photoelectrochemical (PEC) water oxidation and dark CO₂ reduction offers an appealing strategy for solar-fuel production, yet remains largely unexplored in soft metallo-supramolecular systems. Herein, a porphyrin-based Ni(II)-coordinated metallo-supramolecular gel (Ni-CPG) is developed as a dual-functional catalyst for PEC applications. In the PEC cell, Ni-CPG enables visible-light-driven water oxidation acting as a photoanode. To boost the water oxidation performance, a TiO₂ electron-transporting layer (ETL) was integrated with Ni-CPG, creating a type-II heterojunction (TiO₂/Ni-CPG) that facilitates interfacial charge separation and transport. Kelvin probe force microscopy (KPFM) and Mott-Schottky analysis confirm a facile electron transfer pathway from Ni-CPG to TiO₂. The resulting hybrid photoanode delivered a remarkable photocurrent density (∼121.96 µA.cm^-2 at 1.23 V vs. RHE), representing a ∼203-fold improvement over pristine Ni-CPG, with charge transfer efficiency exceeding 63%. In a H-type PEC cell, Ni-CPG is employed as heterojunction photoanode and dark cathode simultaneously, achieving a Faradaic efficiency >94% for selective CO₂-to-CO conversion at 1.57 V versus RHE. Furthermore, in-situ FTIR spectroscopy and DFT calculations unveiled the CO₂ reduction pathway and key intermediates. This study highlights the potential of metallo-supramolecular polymer gel as a dual functional catalyst for water oxidation and dark CO₂-to-fuel production.